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Wo ist die Rennstrecke?
 
DonE's Avatar
 
Join Date: Mar 2004
Location: Brooks, GA
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Cam Chains

Has anyone experienced their cam chains stretching to the point that their tensioners are ineffective?

I decided to replace my carrera type tensioners with mechanical tensioners when I found that when the idle arm (or each pulley arm) was fully extended to take out all slack, there was 1.5mm of space between the top of the hydraulic tensioner and the idle arm. Consequently, there was a lot of slack in the chain which gave me all the noise, especially on start up.

When I install the mechanical tensioners, and adjusted the tensioner in order to take out all the slack, both idle pulleys max'ed out and came in contact with the housings.

I've spoken to two professional engine builders and they are at a loss for an explanation except that the chain was an after-market model and stretched too far. I built the engine and installed the chain - and set the tensioners. This means that when I installed the tensioners, I had to compress the pistons and use pins just to get them to fit. When I pulled the pins, they snapped into place and provided tension.

So, I am looking at a complete engine tear-down to replace the chains. Why would the chains stretch so much?

My cams are GTII EVO's, competition valve springs, and everything else in the valve train is stock.
Old 07-27-2008, 07:12 AM
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Don,

Why not purchase some oversize cam sprockets instead of tearing into the motor? Might buy you some time until the motor needs work that warrants splitting the case.

I used a pair when I put a Frankenstein turbo motor together with a mix match of 3.0 / 3.3 parts.

Tinker

BTW, my motor also make a bit a chain noise from the right bank until its warm.
Old 07-27-2008, 12:18 PM
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It must be that you didn't use genuine chains.

Don, why not replace with a factory chain with a removable link?

Are you sure they couldn't have been shorter when you installed them? I'm wondering if along the way (not driving) your distances between the two cam sprockets has got shorter?
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-27-2008, 01:31 PM
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I'm just thinking out loud here, so my logic might be flawed. But being that our engines are built from the crank centerline outward, in sort of a modular fashion, is it possible that your heads and/or chain boxes were machined to make some C/R or deck-height adjustments? Thus bringing these components closer inward (to the case), and therefore making your chains "longer"?

Once I came to the realization that all of these seemingly tiny tolerances begin to add up and effect other areas of an engine build...I packed up my parts and shipped them out to you know who! I had no faith in my local machine shop to accomodate this type of engine.
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)
Old 07-28-2008, 05:41 AM
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Did you have the sealing surfaces on your heads machined?
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Old 07-28-2008, 08:37 AM
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What some of you might not realize, is that if the Heads, cyl, cam housings, etc, had been machined, which would effectivly make the chains longer than they needed to be, that would have been seen when the motor was first put together. The chains, during the first build up, were the perfect size, not too long, and not too short. The tensioners had the chains tight, and still had plenty of room to adjust the chains if need be... Now, the chains have become so long, there is no more adjusting them, as both the mechanical and hydraulic tensioners have run out of room.
I think if the chains were wrong (length) to begin with, it would have been seen at the point of build up.

We just can not believe that the chains have streched this much.
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Old 07-28-2008, 09:33 AM
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Chains

If your new chains have removable links, just attach the new chain to the the end of the old chain and roll it thru.
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Old 07-28-2008, 10:27 AM
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I remember reading an article once in a Porsche mag, the guy owned a 930 and he used to work for a company that made the chains for Porsche. He was adamant that the chains they supplied Porsche were superior in every possible way.

If you have answered my questions correctly then this must be the only possibility.

I think also there was another solution for fitting chains when they were the wrong length on a rebuild - IIRC I think a company makes very small idler wheels for us.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-28-2008, 01:32 PM
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Wo ist die Rennstrecke?
 
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You guys are good.

The previous owner had the heads shaved a couple mm's to bump the compression, so that shortened the crank centerline to the cam centerline. The chains are probably OK and probably within spec.

I spoke to three engine builders today and all three suspected the engine had been shortened somehow. Jerry Woods said this was common in the late 70's/early 80's on race motors (along with mechanical tensioners) and that's why he makes idler arm tensioner wheels that are 1 and 2 teeth oversized. Good call Tinker - I am going to replace the wheels. After all, if I split the motor, install new chains, the same will most likely happen within 5000 miles again without the new oversized wheels. For your info, all three builders said installing master link chains is a good option too, but it would not solve the problem.
Old 07-28-2008, 03:59 PM
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Don, you've been into that engine more times than a heart surgeon in George Carlin's chest (R.I.P.)! I honestly don't know where you find the resolve!!!
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)

Last edited by sand_man; 07-28-2008 at 04:52 PM..
Old 07-28-2008, 04:26 PM
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Not to get off topic, Don, but I want to see the mechanical bits of your avatar!
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)
Old 07-28-2008, 04:55 PM
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Wo ist die Rennstrecke?
 
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Yep. Just think, until this afternoon, I was ready to rip it apart again. But each time I'm in it, I try to refine or improve something. I'm also going to install the JB Racing adjustable cam timing sprockets. Now I can play with timing in a more civilized way.
Old 07-28-2008, 04:58 PM
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Quote:
Originally Posted by DonE View Post
Yep. Just think, until this afternoon, I was ready to rip it apart again. But each time I'm in it, I try to refine or improve something. I'm also going to install the JB Racing adjustable cam timing sprockets. Now I can play with timing in a more civilized way.
Yeah...I've been eye-balling those on Mike's website!!! Next to Neil, Mike would be one of my very next picks (maybe level pegging) for a "go to shop" that offers such clever solutions! He's da man!
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)
Old 07-28-2008, 06:00 PM
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I just had a look at those sprockets, not sure I would trust them personally. Porsches way is bulletproof.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-29-2008, 11:17 AM
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When you inspected the cam sprockets do they look worn or are there weird wear patterns on the teeth?
Ideally you should change the sprockets on both the cams and intermediate pulley when chains are replaced as they all wear together. Chains (the links) don't actually stretch but the radial clearance between each bushing in the links and the holes in the end links wears and in effect you get an incremental offset between each link in the chain. Multiply that by the amount of links in the chain and the overall length seems to stretch.
Larger idler sprockets is a good idea, and will be the only way to gain back clearance between the tensioner arm and the chain housing and put the tensioner arm geometry back into its designed working range. Jerry Woods seems to know his ****.
Doesn't explain why this was not apparent immediately during the rebuild as soon as tension was put on the chains.
What you really wanna do is replace the chain with a gear set......now that would be killer.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 07-29-2008, 01:39 PM
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Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by NathanUK View Post
I just had a look at those sprockets, not sure I would trust them personally. Porsches way is bulletproof.
If you're talking about the adjustable cam sprockets, they seem to be bulletproof so far. These were recommended to me by a motor builder in CA and said he uses them on his cars and recommends them to customers. JB's been using them on their race (endurance) cars for the past +5 years, so I'm good with it. The simplicity and accuracy you can get using them sounds great.
Old 07-29-2008, 06:07 PM
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Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by fredmeister View Post
When you inspected the cam sprockets do they look worn or are there weird wear patterns on the teeth?
Ideally you should change the sprockets on both the cams and intermediate pulley when chains are replaced as they all wear together. Chains (the links) don't actually stretch but the radial clearance between each bushing in the links and the holes in the end links wears and in effect you get an incremental offset between each link in the chain. Multiply that by the amount of links in the chain and the overall length seems to stretch.
Larger idler sprockets is a good idea, and will be the only way to gain back clearance between the tensioner arm and the chain housing and put the tensioner arm geometry back into its designed working range. Jerry Woods seems to know his ****.
Doesn't explain why this was not apparent immediately during the rebuild as soon as tension was put on the chains.
What you really wanna do is replace the chain with a gear set......now that would be killer.
I rebuilt the motor and don't remember the space between the idler arm (driver's side) and the case being unusual. However, it wasn't something I was looking for either. In any event, the cam and tensioner sprockets will be replaced - it will cost me close to $800 to replace all four. Ouch....
Old 07-29-2008, 06:12 PM
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I know, to do anything right in these cars seems to cost big $$$.
You sound like you're doing it right, no shortcuts, and you should never need to do it again at least for 200k miles. Are you leaving the sprockets on the intermediate gear inside the case then?
How much for the oversize idler sprockets alone from Jerry Woods?
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 07-30-2008, 09:13 AM
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Don, my fear would be that the adjustable part could slip. I just really liked the stock part when I looked at them on my 3.2 carrera. Sure, the JB ones would save some time.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-30-2008, 10:24 AM
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Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by fredmeister View Post
I know, to do anything right in these cars seems to cost big $$$.
You sound like you're doing it right, no shortcuts, and you should never need to do it again at least for 200k miles. Are you leaving the sprockets on the intermediate gear inside the case then?
How much for the oversize idler sprockets alone from Jerry Woods?
$210......each.
Old 07-30-2008, 06:07 PM
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