Home 
Home Search search Menu menu Not logged in - Login | Register
> Jensen Healey & Jensen GT Tech > Ignition > Distributor timing and cam belt on a custom high power engine

 Moderated by: Greg Fletcher Page:  First Page Previous Page  1  2  3   
New Topic Reply Printer Friendly
Distributor timing and cam belt on a custom high power engine  Rate Topic 
AuthorPost
 Posted: 04-17-2020 06:15 pm
  PM Quote Reply
41st Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
discogodfather wrote:
Intake seems to be marked DB3-104? Could that be Dave Bean?Disco,
Have you called Dave Bean Engineering to ask if DB3-104 is theirs? Even if BLL-104 is current, DB3-104 'might' be something they offered before.

Regards,
Tim Engel

Last edited on 05-16-2020 03:57 am by Esprit2

Back To Top PM Quote Reply  

 Posted: 04-17-2020 09:49 pm
  PM Quote Reply
42nd Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
I called Barry Spencer and he gave me really good info. He thought it was a Dave Bean cam so I called them.

Turns out it is a Dave Bean cam, it was one of Dave's propriety grinds called 104 but hotter. They still sell it. It has a .420 lift and 290 duration, 104 lobe centers.

The cam is in pretty good shape so I was going to use it again, also considering the cost of one of these cams from them is $400.

With these numbers cam timing must be even more critical. Amazing these valves aren't bent, but I still have to pull a few and test them. Right now the plan is to disassemble, clean, and check everything. If it's ok then a lap and back together and degree it in properly.

I'll be using the ARP studs, was thinking of upgrading to some Gary Kemp parts, he has a heavy duty spring kit with titanium retainers, chrome moly tappets, solid machined spring bases. Very expensive but tempting.

If things get too hairy it's off to Barry for him to work on. If the seats are shot or any of the valves too bad I was also thinking about going with the sunbeam tiger big intake valves, is that a good upgrade? Was planning to keep things 2.0 for now.

Back To Top PM Quote Reply

 Posted: 04-17-2020 11:29 pm
  PM Quote Reply
43rd Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
One thing that's again bothering me is the info about opening and closing. Ken at Dave Bean didn't seem to have this information, all he could give me was .420 lift/ 290 duration / 104 Lobe Centers. I asked if this meant that the cam could be timed to the Lotus specs for the 104 cam, which Tim generously provided earlier:

LOTUS Cam ID. . . . . 104
Int. Opens, BTDC . . 32°
Int. Closes, ABDC . . 60°
Exh Opens BBDC. . . 60°
Exh Closes ATDC. . . 32°
Overlap . . . . . . 64°
Duration. . . . . . 272°
MOP. . . . . . . . . 104°

Found it kind of odd they don't have the information, they did send me this procedure. Am I missing something here, or do I need more into on the cam grind?

Back To Top PM Quote Reply  

 Posted: 04-18-2020 01:28 am
  PM Quote Reply
44th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
discogodfather wrote:
Ken at Dave Bean didn't seem to have this information, all he could give me was .420 lift/ 290 duration / 104 Lobe Centers.
I asked if this meant that the cam could be timed to the Lotus specs for the 104 cam
Did Ken give you a direct answer to your question?

If not, the answer is, "Yes". Speaking "American-English", in a single-cam Detroit push-rod V8, "Lobe Centers" is the same thing as speaking Brit-English and saying "MOP" (Maximum Opening Point). So timing the DB3-104 cam to 104 "Lobe Centers" is the same as timing the Lotus 107 or 104 cams to 104 "MOP". Use the Lotus Green-dot, 104 MOP pulleys.

Regards,
Tim Engel

Last edited on 04-18-2020 01:31 am by Esprit2

Back To Top PM Quote Reply

 Posted: 04-18-2020 03:03 am
  PM Quote Reply
45th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
"LOTUS" Cam ID . . . C. . . . . . . D . . . . . . . E. . . . . . "104" .. . . .105. . . . . 106 . . . . "107" . . . . 108
Int. Opens, BTDC . . 26° . . . . . 25° . . . . . 27.5° . . . . 32° . . . . . ??° . . . . . ??° . . . . . 22° . . . . . ??°
Int. Closes, ABDC . . 66° . . . . . 65° . . . . . 52.5° . . . . 60° . . . . . ??° . . . . . ??° . . . . . 50° . . . . . ??°
Exh Opens BBDC. . . 66° . . . . . 65° . . . . . 52.5° . . . . 60° . . . . . ??° . . . . . ??° . . . . . 50° . . . . . ??°
Exh Closes ATDC. . . 26° . . . . . 25° . . . . . 27.5° . . . . 32° . . . . . ??° . . . . . ??° . . . . . 22° . . . . . ??°
Overlap . . . . . . . . . 52° . . . . . 50° . . . . . 55°. . . . . . 64° . . . . . ??° . . . . . ??° . . . . . 44° . . . . . ??°
Duration. . . . . . . . . 272° . . . . 270° . . . . 260°. . . . . 272°. . . . . 296° . . . . 320°. . . . 252° . . . . 304°
MOP. . . . . . . . . . . . 110° . . . . 110° . . . . 102.5° . . . 104°. . . Per Event . Per Event. . . 104° . . Per Event
Lift. . . . . . . . . . . . . 0.340". . . 0.350" . . . 0.344" . . . 0.420" . . . 0.433" . . . 0.450". . . 0.378" . . . 460"

The A & B cams were development cams, and I've never seen specs published for them. The 105, 106 & 108 were competition cams that Lotus never sold to the general public. I only mention them to fill out the 'naming' number series.

Then Dave Bean sells a BLL-104, BLL-105 & BLL 107 that apparently do NOT mimic the original Lotus 104, 105 & 107. And to add further confusion, It appears that Dave Bean also sold/ sells (?), a DB3-104. Is that a BLL-104 with a different name, or is it yet again different. And are there other CB3 cams?

DBE. . . . . . . BLL. . . . . DB3 . . . . BLL. . . . . BLL
Cams . . . . . 104. . . . . 104 . . . . 105. . . . . 107
Duration . . . 290° . . . . 290° . . . 295° . . . . 270°
Lift . . . . . . . 0.420". . . 0.420" . . 0.425". . . 0.375"

Delta Motorsports sells the same BLL series of cams that they seem to be getting from Dave Bean Engineering. Unfortunately, they've not been able to get any more information out of DBE than you or I.

In either case, if you have heard about the Lotus 107 cam improving the 907's low-end torque and driveability, the BLL-107 cam is NOT the same. Durations of 252° for the Lotus cam, and 270° for the BLL cam can NOT give the same result.

Similarly, if you're thinking about a Lotus 104 cam with 272° duration for a street-hot cam, the BLL-104 with 290° duration is NOT the same.

I mentioned earlier that I bought a pair of "104" cams on eBay, and they turned out to be "Delta 104" cams. What's that? Delta Motorsports knows nothing about them, and Delta Cams disavows any knowledge of them. But they are not the same as Lotus 104 cams, and I don't know what they are.

If you go out into the market place shopping for a 104 or 107 cam, what is it that you really have in mind? In the early days, when J-H owners started swapping cams to improve low-end torque and driveability, the Lotus 107 was all there was and they liked it. It was only after other vendors wanted some of the action that other 107's began to show up. Same with Lotus 104 cams being first, and others coming along later to muddy the waters.

Established names provoke certain expectations. I do wish that aftermarket companies would either accurately clone the originals (may be intellectual property issues involved), or be creative enough to come up with their own names for different products.

Personally, if a cam doesn't say Lotus on it, I don't know what it is.

Regards,
Tim Engel

Last edited on 05-16-2020 11:07 pm by Esprit2

Back To Top PM Quote Reply  

 Posted: 04-18-2020 03:24 am
  PM Quote Reply
46th Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
It frustrates me. Without the specs who knows whats really going on. Dema Elgin taught me years ago that the way people bought aftermarket cams was to rip the sheet out of the catalog, pin it to the wall, and then throw a dart at it and pick the cam it landed on.

He also taught me to measure and plot a cam, which my dumb mind forgot years ago. I should have payed more attention.

Who does sell an actual 104 cam? I see Greg Fletcher has it advertised as a genuine Lotus grind. I'm tempted to go this route just so I know whats going on and eliminate some of the "secret sauce" variables.

Ken seemed to indicate that Dave was especially secretive about their proprietary grinds.

Back To Top PM Quote Reply

 Posted: 04-19-2020 08:06 am
  PM Quote Reply
47th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
Here's a basic sketch of the 'Lotus' 104 cam lobe.

Attachment: Cam - 104 Lobe drawing.jpg (Downloaded 124 times)

Back To Top PM Quote Reply  

 Posted: 04-19-2020 08:07 am
  PM Quote Reply
48th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
And a similar one for the 'Lotus' 107 cam lobe.

Attachment: Cam - 107 Lobe drawing.jpg (Downloaded 124 times)

Back To Top PM Quote Reply

 Posted: 05-14-2020 05:21 am
  PM Quote Reply
49th Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
So, ready to bolt on the heads, just waiting for a couple extra shims to get me to .007" and .012" on intake and exhaust. So much easier to do this when the head is off!

So my veiner pulleys had no real objective marks other than the little bits of paint I had used to line everything up in the past. Now I am ready to bolt it all together and degree the cam, got a very nice setup on load from a friend.

Problem: if you don't even have the initial idea of where the cams should go (this would not be the case if I had the green dot pulley to use with the 104), then how to you bolt it up.

My solution: I put the cam towers in place and have everything shimmed correctly, then measured the intake and exhaust valve opening and closing points, roughly. The RED dots on the pulley I marked are those events. I then looked at the cam info for the 104 from Tim, and it says:

Intake Opens 32 Degrees BTDC
Exhaust Closes 32 Degrees ATDC

So, the cam rotates at 1/2 the crank speed in a 4 stroke, regardless. I took 32 degrees, devided by two to get the cam degrees (it's my understanding all cam data is always in crank degrees) and then used a protractor to measure and rotate the cams into the correct position they should be AT TOP DEAD CENTER. Those are the WHITE marks.

So now I have a very rough objective point to start with when bolting the cams in place, the next step is to actual degree it in on the engine.

Question: Is there any data for the 104 cams at .050" or some kind of lift? It's hilarious that Dave Bean sent me a big write up on how to degree in cams that completely emphasizes the importance of degreeing at lifts and how it's much more accurate and better, but then no information about timing their cam!?

I looked all over the Internets and no one seems to have data at any lift. I guess I will just have to use the data at zero lift.


Back To Top PM Quote Reply  

 Posted: 05-16-2020 06:26 am
  PM Quote Reply
50th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
discogodfather wrote:
So, ready to bolt on the heads, just waiting for a couple extra shims to get me to .007" and .012" on intake and exhaust. So much easier to do this when the head is off!Disco, are you shooting for 0.007" & 0.012" dry during trial assembly? What sealant will you be using between the cam carrier and head. If it's an anaerobic sealant, like Loctite 518, then it's film thickness is 0.0005" (half a thousandth). In that case, dry-shim short by that half a thousandth to 0.0065" & 0.0115". Then the film thickness will 'float' that dry setting up to 0.007" & 0.012" during final assembly with the sealant applied.

discogodfather wrote:
(Snip)... I took 32 degrees, divided by two to get the cam degrees (it's my understanding all cam data is always in crank degrees) and then used a protractor to measure and rotate the cams into the correct position they should be AT TOP DEAD CENTER. Those are the WHITE marks.Here's a way to double check your work.
If you had stock pulleys installed with the timing marks aligned ON the centerline between the cams, and...
If you removed the nut & washer so you could see the ends of the camshafts in the pulley bores, then...
You would see that the keyways are located above that centerline between the cams.
The intake keyway is in the upper-left quadrant, at about 10:00 o'clock
The exhaust keyway is in the upper-right quadrant, and about 2:00 o'clock.

Each cam MOP has it's keyway a certain angular distance (degrees) above that centerline between the cams.

_97° MOP = 21.25° . . . . 97° is the Blue timing dot on a SINGLE-MOP pulley.
100° MOP = 19.75° . . . 100° is the Blue timing dot on a DUAL-MOP, Red-dot / Blue-dot pulley.
104° MOP = 17.75°
105° MOP = 17.25°
110° MOP = 14.75°
115° MOP = 12.25° above the centerline between the cams

The trick (and the Achilles Heel) will be in accurately locating the radial centerline of the keyway, and the centerline between the two cams, and accurately measuring the angle between them.

discogodfather wrote:
Question: Is there any data for the 104 cams at .050" or some kind of lift? It's hilarious that Dave Bean sent me a big write up on how to degree in cams that completely emphasizes the importance of degreeing at lifts and how it's much more accurate and better, but then no information about timing their cam!?First, not all 104 & 107 cams are created equal. Unfortunately.
Lotus designed the originals, and named them. Then, every Tom, Dick & Harry aftermarket cam grinder on the planet came out with their own 104 & 107 cams with different timing specs. That has created great confusion... why couldn't they have exercise a small shred of naming creativity for their own cams.

You're using Dave Bean BLL-104 cams, which are slightly different and call for 105 MOPs, so you should use Dave Bean's instructions... not Lotus' instructions.

Unfortunately, Dave Bean himself passed away a couple of years ago, and he was 'the' tech guy, 'the' engineer at DBE. And he didn't share much of the details about things he developed... including cams. The sales staff do not know the answers to your questions. I recently asked Ken Gray at DBE to contact their cam grinder, talk with an engineer, and get all the info about each of the cams they're getting from that company. He said he would. That doesn't help you for now.

I have old Dave Bean BLL specs from the mid-1990s... I can guarantee the BLL design hasn't been changed since then, but...

Lotus 104 = 32° / 60° / 60° / 32° -- 272° Duration -- 64° Overlap -- 104° MOP
BLL - 104 = 31° / 61° / 61° / 31° -- 272° Duration -- 62° Overlap -- 105° MOP

Lotus 107 = 22° / 50° / 50° / 22° -- 252° Duration -- 44° Overlap -- 104° MOP
BLL - 107 = 24° / 54° / 54° / 24° -- 258° Duration -- 48° Overlap -- 105° MOP

Lotus never quoted duration at any specific lift value, such as 0.050". Nor did they say duration was seat-to-seat, or not. Nor quote an angular position off of TDC at which 0.050" lift occured... either opening or closing. So, no direct answer to your question.

However, I knew an engineer at Lotus (retired), and he gave me the information on the two cam illustrations I posted above. He further stated that Lotus quoted duration between the tops of the opening and closing ramps. You won't find that in print from Lotus, but the info on the illustrations I posted is all per that engineer.

If you look at the two cam illustrations, keeping in mind that Lotus quotes cam duration between the tops of the opening and closing ramps, look at the ramp dimensions and you'll see that the 104 cam's opening & closing ramps are 0.010" high, and the 107s are 0.012" high. That's as close as you're going to get to a "measuring height" from Lotus, but it's not 0.050"... ADAPT.

In the 104 illust'n, the profile contour is 68° before, and 68° after MOP (ie, straight up centerline), or 136° total expressed in 'cam' degrees. But timing is expressed in crankshaft degrees, so 136° x 2 = 272°... which is the duration that Lotus quotes for the 104 cam.

If you start with your dial indicator zeroed on the base circle, rotate the cam until the dial indicator 'just' reads 0.012". Note the angular position on the degree wheel... you should have rotated 20° to that point. Rotate the cam, up over the hump and back down, until the dial indicator once again 'just' reads 0.012", and note the position on the degree wheel. You should now be at the top of the closing ramp.

The difference between the two degree wheel readings (from 0.012" before to 0.012" after) should equal 272° for a 104 cam... +/- manufacturing tolerances.

One half the difference between the two degree wheel readings is the half way point of your rotation, which is also be the lobe's Maximum Opening Point (MOP).

Regards,
Tim Engel

Last edited on 05-16-2020 07:47 am by Esprit2

Back To Top PM Quote Reply

 Posted: 05-16-2020 06:32 am
  PM Quote Reply
51st Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
discogodfather wrote:
It's hilarious that Dave Bean sent me a big write up on how to degree in cams that completely emphasizes the importance of degreeing at lifts and how it's much more accurate and better, but then no information about timing their cam!?Disco,
Would you please forward a copy of Dave Bean's write-up as a file attachment to a PM. I'll read through it and see if it makes sense.

Regards,
Tim Engel

Back To Top PM Quote Reply  

 Posted: 05-16-2020 07:35 am
  PM Quote Reply
52nd Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
Esprit2 wrote:

If you removed the nut & washer so you could see the ends of the camshafts in the pulley bores, then...
You would see that the keyways are located above that centerline between the cams.
The intake keyway is in the upper-left quadrant, at about 10:00 o'clock
The exhaust keyway is in the upper-right quadrant, and about 2:00 o'clock.



The keyway for these cams is cut right on the intake/exhaust lobe centers. The wheels are the Dave Bean veniers (square tooth) and they have some arbitrary 2 degree timing marks that line up with the intake and exhaust opening/closing events. The keyway for the intake faces at about 9/10 o'clock when at TDC, the exhaust at about 3-4 o'clock.

The intake lobe and the exhaust lobe positions, as I marked them, have both the intake slightly open (just opened) and the exhaust slightly open (about to close). Does that make sense? If I clock the intake at 10 o'clock (upper left hand quadrant) they will be about 100 degrees from opening, and the exhaust at 2 o'clock (upper right hand quadrant) would be about 100 degrees after closing.

Last edited on 05-16-2020 07:37 am by discogodfather

Back To Top PM Quote Reply

 Posted: 05-16-2020 08:19 am
  PM Quote Reply
53rd Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
I think I just answered my own question- cam timing is always TDC on the compression stroke. I think I measured it up for TDC on the intake stroke. Both valves need to be closed, correct? So that would explain why I am 180 degrees from what Tim suggested: intake at 10 o'clock and exhaust at 2 o'clock, just for an initial setting to bolt down the cam towers and get everything ready.

Back To Top PM Quote Reply  

 Posted: 05-16-2020 05:50 pm
  PM Quote Reply
54th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
discogodfather wrote:
I think I just answered my own question- cam timing is always TDC on the compression stroke. I think I measured it up for TDC on the intake stroke. Both valves need to be closed, correct? So that would explain why I am 180 degrees from what Tim suggested: intake at 10 o'clock and exhaust at 2 o'clock, just for an initial setting to bolt down the cam towers and get everything ready.Cam Timing is always spec'd, and timed with the #1 cylinder at TDC. That's your starting point.

The cam lobes need to be where they need to be... they stay put. Then the adjustable pulleys allow you to then rotate the outer rim & teeth as need be to mate up with the timing belt. The timing belt is in a fixed position by the crankshaft, which by definition is not allowed to rotate off of the TDC position during timing... so the belt can't move either. The pulley rim must go to the belt, without disturbing the cam lobe positions.

Anything that affects the distance between the crankshaft centerline and the camshaft centerline affects the amount of slack in the un-tensioned belt loop (tensioner backed all the way off). The crank must stay at TDC (it can't be allowed to move), so the slack in the belt strand between the crank and the exhaust cam pulley must go up and over the pulleys to/ or from the tensioner... rotating the pulleys a little.

If the head and/or cam carriers have ever been milled to flatten a warp, if the block has ever been decked, or just a simple stack-up of production tolerances... anything that alters the "PERFECT" center-to-center distance also alters the amount of slack, and hence, the positions of the cam pulleys at TDC, and the alignment (or lack there of) of the timing dots.

So, the cam lobes need to be where they need to be when at TDC, and the adjustable pulleys only allow the rim to be moved as necessary to follow the belt that might be moving as non-standard slack is pulled out of the timing belt. Make sense.

I previously gave you angular locations for the cam/ pulley keyway locations above the centerline between the two cams. That is where they (and the lobes) need to be when the crank is at TDC. Now you're just screwing around with the pulley rim.

NOTE: Head gasket thickness has a large affect upon the slack in the timing belt loop. Therefore, degreeing the cams is done 'after' the engine is fully assembled and the head is torqued down (gasket it crushed to final dimension). Only then can you accurately 'degree' the cams.

You are trying to pre-set the adjustable pulleys to a ball park setting (close, but not spot on) with the head off the engine. Don't confuse that with actually 'degreeing' the timing as a final procedure.

See the attached JPEG. JHPS only allows a 100kb maximum file size, so that's all the resolution I can give you here.

The intake cam lobe is shown in three positiions. The one pointing down & right is MOP... the intake valve is at it's Maximum Opening Position. The lobe to the upper left is where it would be when the #1 cylinder is at TDC. There's a note in bold red font, "To Red Centerline, 14.75° degrees... that's for a 110° MOP. In the lower right corner of the page, there's a chart of angular dimensions for other MOPs, and 105° MOP is 17.25° degrees above the centerline.

You can either:
1) McGyver a way to establish a 'working' centerline between the two cams, and a protractor or cut pie wedge to indicate 17.25° above the centerline, or...

2) Put a degree wheel on the cam, and a dial indicator perpendicular to the tappet (NOT on the lobe itself). Rotate the cam to find the Maximum Opening Point via the dial indicator, and zero the degree wheel. Now use the attached drawing to map your way (rotating the cam) to the 17.25° dimension above the centerline between the cams.

The details for the exhaust cam lobe are just the mirror image of the intake lobe, so they're not included on the drawing.... just a red centerline for where the keyway should end up.

In either case above, the result will be a rough, ball-park approximation of where the cam should be... ignoring all the factors that can affect the amount of slack in the timing belt prior to tensioning. Now, with the keyway's located, you can move the pulley's rim to align the timing dot with the centerline between the cams.

But be aware that timing with the head on a bench is not allowing for head gasket crushed thickness, or for any past milling of parts. Install the head on the engine, and the end result of this work will be wrong to some small degree. But not by enough to bend a valve as the head is torqued down.

Now the real work begins, and you can do a proper job of degreeing the cam timing with the #1 cylinder at TDC.

Good luck,
Tim Engel

Attachment: 9XX Cam Timing - Pulley & Cam Keyway Orientation - Cyl Head DRAWING.jpg (Downloaded 92 times)

Back To Top PM Quote Reply

 Posted: 05-16-2020 09:57 pm
  PM Quote Reply
55th Post
Esprit2
Member
 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
For those interested, I've posted a copy of the Dave Bean instructions for how to 'degree' adjustable cam pulleys in the 'Files' section of the Jensen-Healey Facebook page. You can download a copy over there.
https://www.facebook.com/groups/102760143109766/files/

Chris & I discussed the following during our email exchange, and I'm including it here since it kinda completes the thoughts in the previous couple of posts.


May 16, 2020, 12:48PM, Chris Morlock, aka Disco, wrote:
Yes this all makes sense.  I am just trying to get a ballpark starting point so I don't end up smashing valves on the piston head when I bolt everything down.  Next step is to torque the head and then actually degree the cam in measuring all the way.


May 16, 2020, 1:14PM, Tim Engel, Esprit2, wrote:
Chris,
Before installing the head on the block, it's standard procedure to turn the crank to 90 deg BTDC. That puts all the pistons halfway down their bores, and well out of the way of any valves.

After the head is torqued down, and the cam carriers bolted on with sealant, then gently return the crank to TDC. Use a little mechanical empathy while turning the crank, and stop immediately if the crank clunks to a stop. That clunk would be a piston hitting a valve, so don't force it. Back-off and tweak the cam positions as required to move any 'full open' valves to partially closed. Then proceed to TDC.

Once at TDC, you can install the timing belt and get into degreeing the cams per Dave Bean's instructions.
(Snip)...
Later,
Tim 

Back To Top PM Quote Reply  

 Posted: 06-19-2020 10:39 pm
  PM Quote Reply
56th Post
discogodfather
Member


Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
Status: 
Offline
Well, everything is back up and running. After taking the head off I have successfully done my own valve job with a set of Neway tools, resurfaced the valves and ground new seats. New shims and everything went together well.

Got the cam degree'd in and spent lots of time with it to get a very good feel of what was happening. With the help of Tim I was able to find MOP using the excellent Dave Bean guide, and confirmed a 272 duration with opening and closing points at around 31 and 61 degrees. I marked up the cam pulleys with lots of info- opening and closing points, MOP point, and the arbitrary TDC marks to line everything up for service in the future.

Wow was it difficult to get a setup to measure the tappet movement. There is practically no access to the back of the tappet because the cam is hogging all the real estate. I had to use a very thin extension for my dial gauge, and then it was very difficult to get a solid reading because it was always at a slight angle. I kept trying and finally got something close to a perfect parallel angle to the valve travel. We're talking about 2mm of space if everything is lined up correctly and I needed to grind a relief into the dial gauge extension to get it to fit.

One thing I have noticed is that if you can't get the full 360 degrees of rotation and actually measure the travel on the tappet fully across its travel, it's really a waste of time. You need to see the full travel to accurately measure MOP, period. Taking a partial measurement and finding the opening or closing points or trying to extrapolate the MOP is silly.

The Dave Bean directions were very good once I wrapped my head around the concept. At first I didn't really understand, but the method of finding the MOP and going from there is very helpful, as well as taking measurements at higher lifts. At zero lift, your reading error is highly magnified. Also, there is a dwell at MOP and you have to measure it and average out where exactly it is- sometimes a few degrees of rotation yields the same reading.

In general it helps to have a deal gauge that is digital and reads in .0005" instead of the usual .001". When using an analog gauge it gets confusing as to what rev you are on (even if it has the little rev counter built in). With the digital, it simply reads the position in absolute terms with no fuss.

It's difficult to get a setup to hold the gauge well. Most kits come with a magnetic base and there really isn't anything magnetic to actually clamp to anywhere on the Lotus 907. I ended up taking an iron plate from my hydralic press and setting it on top of the flats of the intake manifold and kind of wedging it against the cam tower hoops. This provided a very nice, stable, and heavy base to clamp the arm to. I initially tried with a disc brake rotor measuring kit which has a flexible metal arm- it was useless and way too wobbly.

Another thing that helps immensely is a quality degree wheel. I first used a simple Jegs kit that was made of basically an aluminum that wasn't much thicker than a soda can, and these things can be bent just looking at them. I returned it to Amazon because it insulted my intelligence. A friend lent me a monsterous 1/4" thick aluminum degree wheel that was easily 20" in diameter. It was so stable and beefy you could turn over the crank by just grabbing the wheel- it felt like I was in the Navy on a boat opening a door. Because the actual degree wheel being such large diameter it makes the resolution that much more accurate in terms of the degree measurements.

My setup process is what Tim recommended and it went flawlessly:

1) Make sure the crank is at 90 degrees (all piston at about midway travel)
2) Install the cams at the 10 o'clock (intake) and 3 o'clock (exhaust) position (guesstimate in my case because NO pulley marks, on the green dot you just line it up). Bolt it down and check shimming if needed.
3) Gently raise the crank back up to TDC. If you feel anything, back off and reposition the cams. Make sure nothing is touching.
4) Install the belt and rotate the crank a few times to visually confirm all marks line up (since I had no marks I made some temporary ones)
5) Degree the cam, starting with the MOP point. Measure everything and mark it on the cam pulley.

I ended up using my adjustable vernier pulleys to help eliminate slack in the belt and get everything to a very high tolerance. Usually the vernier is set at a 0 degree arbitrary point so that, in the future, you can slightly retard or advance the cam for tuning purposes. I didn't see too much of a reason to do that and instead simply found the most accurate position to achieve the correct timing.

Thanks to everyone that helped! She started up right away and I can already tell that my years of deteriorating performance was most likely due to really bad cam timing.

Back To Top PM Quote Reply

Current time is 07:07 am Page:  First Page Previous Page  1  2  3     
> Jensen Healey & Jensen GT Tech > Ignition > Distributor timing and cam belt on a custom high power engine Top




UltraBB 1.172 Copyright © 2007-2011 Data 1 Systems