Both chains should be the same length. i wonder if these chains are longer than normal.

Truth! I'm sorry I'm up here in PDX and can't come down to give you a hand too (not that I'd be much help ;) )

I really haven't had any trouble with the motor, aside from the JB Weld on the back of the left cam housing covering the ilder arm shaft popping off. Seeing that shaft there in the hole with oil seeping out had me thinking sad thoughts of pulling the engine and rebuilding it. But, thanks to p156 of Wayne's book ;) , I'm happy again. Now I just have ot finish installing the front oil cooler...good thing the monsoon season isn't over up here yet.

Keep us posted....

Wow what ws that post all about?

Just me blathering to Rich here rather than email. I purchased the 2.7 from him that was in the batch of engines he's talking about and have not had any problems with it yet... sorry.

Rich: IMHO you still have a problem. If there was so little clearance, after some running, the parts will hit again. I think those chains are too long. Count the links and compare the # to a new chain. You may still have to install a ML. Good luck.

In response to John, I am concerned why there was air between the top of the Carrera tensioner and the idler arm, but that picture was taken once the sprocket was jammed onto the lip and lifted the arm clear of the tensioner

The engine is a mystery as I have said before, but it looks like it was put together by someone who knew what was going on and perhaps the mechanical tensioners were used for reason that they were the right tool for this job. Perhaps somebody built it as a race motor. The cams were installed retarded about 6 degrees which would bring in the top end more and I am beginning to wonder if the heads have been milled significantly because the engine starts like a high-compression engine -- sort of like my Z/28 with 11:1 CR -- that sort of slow R-R-R then suddenly vroom. The intermediate shaft gears are new, the heads were newly redone with new valves, etc. I don't know any way to determine what is inside this engine and resolve the mystery for certain without disassembling it and that is not going to happen.

The point that keeps nagging at me is that there was't a problem with the mechanical tensioners installed. I turned it over many, many times on the engine stand with the solid tensioners and never had a problem and I am thinking of going back to what the builder installed in the first place. Since the reliability of the solid tensioners is 100% -- can't fail -- it would give me some peace of mind to know the chain isn't slapping wildly around. I know the solid tensioners are generally considered a racing part, but if the Lotus guys can live it it perhaps so can I. If I only have to adjust them every 3000 miles, that would be OK with me because it is only a fun car and I could live with doing this once or twice a year.

Although the solid tensioners are not ideal, could I get by with this? Are the solid tensioners the lesser of two evils?

If so, how tight should I set the mechanical tensioners? I need to allow some room for the expansion of the engine don't I?

Thanks,

Rich

Mechanical tensioners will leave you where you are right now. Switching to pressure fed tensioners, should not have made a difference in the position of the idler wheel. That is determined by the length of the chain and number of teeth on the gears. If it was fine with solid tensioners, then it should be fine with pressure fed tensioners. Its not, so something has gone wrong.

To review:
The idler arm geometry does not look correct Due to tolerance stack from prior machining or combination of parts, the chain now has too much slack. The mechanical tensioners probably have more adjustment travel than the hydraulic tensioners which might be why it didn't have this symptom before. However, I wouldn't use the mechanical versions to mask this situation. The prior messages all contain valid suggestions and observations.

Some additional thoughts:
- Just because the PO installed new parts doesn't necessarily mean it was put together correctly. Have you ever seen a new house or remodel that was built like s**t? Plenty of those around too. Depending who did it, DIY may not have been the best solution.

- Don't assume anything. Check and recheck yourself.

- Compare the geometry of your idler arm with pics from other sources (factory manual, Waynes' books, B. Anderson's book). Did I mention the idler arm is NOT in the correct position?

- If you want to take this further, as suggested, check the chain length (too long) and/or explore using oversize idler sprocket wheels.

- Using mechanical tensioners may be the easy solution for the short term, but it's your engine. You decide.

Your move,
Sherwood

Whoops, I had forgotten about the mechanical tensioners. This makes sense now. The mechanical tensioners offer no relief at all, so stresses on the chain are relieved through the chain itself! As a result the chain S T R E T C H E S.

Dude, replace your chain and don't look back. Use the master link chain - it only takes a few hourse to loop it through there. The more your chain stretches, the more your timing will be off, resulting in decreased performance, and possible interference with the pistons and valves (possibly reducing your potential rev-limit).

You have a whole host of problems with this chain, I wouldn't risk it unless you really want to do a $6K rebuild...

-Wayne

Plates stretch.
Compare a new and an old bike chain. There can be inches in length difference.
If it is a 108 link chain, and each plate stretches 1mm. Thats 10.8 cm.
Even 0.2mm per link is 2 cm
How many links in the 911 timing chain? Say 98?
For 2cm stretch that is 0.2mm per link............

The metal link plates don't actually stretch, but the link holes elongate and the link pins wear. Multiply by the number of links and the increased length can make a difference (but this much?). The increased distance between the links creates excess friction and wear when in contact with the sprockets which are a fixed distance apart. Compare with a new chain just to make sure. However, at this point, you'll have to split the case to remove them, or replace with a master-link type chain.

I suggest machining tolerance stack (crankcase, cylinders, cylinder head) has more to do with this than chain wear, but check both.

Sherwood

OK, I give up. You guys have convinced me that something is weird with this engine. However, I am at the end of my available time and sanity. As Dirty Harry said, "A man has got to know his limitations." So it is time to call in some professional help otherwise I am never going to be able to drive it with an easy mind. I called Wayne Baker's shop here in San Diego. They do a lot of two liter race engines and there was a 904 and two 910s in the shop the last time I stopped by. They were nice on the phone and I talked to them for quite a while, they offered a couple of explanations. In any event, it sounded like they had a pretty good handle potentially solving this weird problem I am just going to take it over to them and live by what they say.

For what it is worth, I did drive it around the block a couple of times and it certainly seems to run well but I am not going to go against the collective knowledge of this group and hope for the best. I don't want it to blow up on me at this point.

Thanks again for your help and I will keep you posted on what the verdict is.

Rich

Rich

Here is my thought after seeing the setup. I bet the heads have been milled and the chain is a little shorter. However, I do not think it is short enough to remove one link. I think it will be OK. The amount of the sprocket that was caught was so minor and that is why I feel this way. Talk to you soon.

FYI, here is the after picture of the cam housing.

http://forums.pelicanparts.com/uploa...tensioner2.jpg

As you can see there still appears to be plenty of tension on the chain. Does this picture shed any other ideas or comments?

Well, just an update for those interested in this weird little project.

As I indicated in my last post, I made an appointment and took it to the mechanic to try to solve this matter once and for all. Well, after reviewing the photographs and talking about it more, it seems that he does not want to deal with this issue because of a lack of history with the car and engine and can only really address this with a complete rebuild. $$$$$ Suffice to say, this is not going to happen. So, it is back to my garage to fix this.

Based on the extensive discussion on this point, the only thing that I can address without pulling the engine and tearing it apart is to assume that the chains have stretched and were not replaced with the rebuild. So, the next step is to put on the new Porsche master link chains and see if it cures the problem. I know that they are not the ideal solution, but I guess this is going to be a "drive it until it explodes" type of motor.

I do have a couple of questions before I begin:

(1) What is the proper method to get the old chain off?

(2) Do the sprockets look excessively worn in the photos? Can I get by without replacing these?

(3) What is the best way to snake the new chains over the intermediate shaft sprockets? Has anybody else done this?

(4) Regarding the pressure fed tensioners, would there be any advantage to using the non-pressure fed tensioners with the safety collar? I guess I will need to replace the chain and see how things line up to determine what is going on for sure in this regard.

Thanks again for your help and patience with this project. I thought I was finished bugging you guys about this but I guess I am doomed to solve this problem myself.

Rich

PS: It drove pretty well (I drove it very conservatively) all the way to the shop but it seems to have good power and a completely clean exhaust. Plus, the temperature stayed below 180 degrees with just the engine oil cooler. I was careful to maximize the cooling (trimmed cylinder dividers, routed more air to the oil cooler, sealed the fan shroud with insulation, etc.) The front oil coller is a problem for another day. I am going to start looking at my 2.0 liter E-spec rebuild. This time, with the help of Wayne's book, I will know everything about it. Thanks again for the book Wayne.

Oops -- hit the send button twice!

Rich

Rich,

The best way to remove the chains is to use a chain breaker purchased from a bicycle shop. The breaker will push out a pin in the chain and enable you to attach the new chain to the old using the master link. Once you have the new chain attached to the old chain, rotate the engine and feed the new chain through around the sprockets. Do this on both sides. Remove old chain and affix the master link on the new chain. Make sure that the open end of the master link is facing the opposite direction of chain rotation.

removing the chain housings makes the job a whole lot less of a hassle. then the chains just hang, instead of bunching up in the housings. i use a disc cutter to grind off the "riveted" ends of one link, and some sidecutters to persuade it apart from there. attach the new chains to the old chains (use the new link) the same distance out of the engine on both sides, so when you roll them thru, they come out together. starting with the engine on #1 TDC, the left cam needs to be turned one "lump" over, so the pistons don't interfere with the valves, and the right cam can stay put. the crank can now be rotated without interference. attach the ends, and reposition engine to TDC #1, turn the left cam back to where it was, with the keyway facing up, and reattach the sprockets, etc, then do the cam timing.

Charlie:

Can I turn the engine over and and still have the cams turn appropriately so that I do not have to retime the camshafts? I am having a bit of a difficult time visualizing this. Where do I start, from the top or the bottom? I would imagine the top to ensure that it maintains tension on the chain around the intermediate shaft sprocket?

Couldn't I just tie the old chain to the new chain as you suggest and feed it / guide it over the intermediate shaft sprocket without turning the engine. I am a bit paranoid about having it jump a link and then not knowing what to do.

Thanks

Rich

John:

I was responding to Charlie while you were posting. I guess it would be a lot easier with the chain boxes out, but is there enough room in there to allow the chain to pass over the intermediate shaft sprocket and feed the new chain without removing the chain boxes and retiming the cams? Maybe I'll practice this on one of my other engines and see if I can do this. Otherwise, off to the cam timing issue.

It sounds like the sprockets don't look horrible to you. Is that correct?

Thanks again for your valuable assistance. I wish you lived nearby. Do you want a plane ticket to San Diego to come and do this!

Rich

Sorry Rich....I didnt take into consideration you have the heads on and the cams timed. Should have picked up on this when you mentiond that you just DROVE IT!! I was just thinking through how I'm going to be doing mine......my heads and P/C's are off.

Your chain is not on the intermediate staft sproket completely or is completely off from it. I had the exact same symptoms you have (but it was still on the engine stand) engine would turn one way, almost all the way around and ckink stop. Its REALLY hard to see if the chain is indeed on both sprokets. I cannot imagine how it could be put back on in the car. ON an engine stand you can put the disconnedted cam up and the chain will hang. You can then try to manover the chain down and sideways to get it back onto the sproket.

NO chain will stretch this much without breaking. IF the tensioners this far in the chain MUST be off the sproket, WHAT else coud it be?

read the entire thread jack, we're way past that.

you will have to retime the cams, so put that thought out of your mind. and you can't feed in the chains without turning the crank. re-read my previous post.

Not sure if the problems has been 100% indentified (not familiar enough with 911 specific engines to be sure) but there may be two factors at play:
1) machined case/heads which reduces "deck height"
2) worn-out chains due to mechanical tensioners

#1 may have been done to increase the compression ratio (i.e. heads machined) and/or true the case. This will reduce the distance between the cams and crank, create a slack chain, and retard timing.

#2 may exist because of the existance of mechanical tensions. These are a Bad Idea because they can not deal with the motion of the chain and cause excessive loads in the system. These loads cause excessive wear, and lead to a "stretched" chain. I say "stretched" because the metal does not actually stretch, but the pins become smaller, and the holes in the links become larger. Typically 0.5% elongation is the max, mainly because of tensioner travel and cam timing.

Seeing as how the timing was already retarded 6 degrees, I would say it was more an indication of an elongated chain or insufficient cam/crank distance. Chances are the heads/case weren't machined excessively, and the chain could be replaced with a brand-new one. Mechanical tensions will just wear out a new chain in short order, even if the tensioner itselfs appears to last forever...

Best of luck.

Matt Beaubien
'73 911E

John:

Thanks -- sorry I didn't understand your previous post about not being able to feed the chains without turning the crank. I'll start amassing the stuff to do this

Now this may be a bit incredibly silly, but I did find this "link" from an alternative vendor which is supposed to be for the 911 timing chain. Is it possible to just remove a link and insert this new "master link" to make my existing chain the equivalent of a "master link" chain.

http://forums.pelicanparts.com/uploa...Chain Link.jpg



Snowman: I thought that was the problem initially, but Keith and I both checked and it is on the sprocket. I have put 25 miles on the car back and forth to the shop.

Mr. Beau: If 0.5 percent is the maximum stretch these things can achieve it seems really weird that it would have this much slack. Anyhow, it is probably a combination of both factors.

Rich

What sense would there be in just putting a ML in your old chain?

If no machining has taken place to shorten the cam/crank centerline, then the chain is too long. In your case, it's probably more than 1%. 1% may not sound like a lot, but when it comes to chain wear, it is, and could have easily been caused by solid tensioners (which is why you constantly adjust them--to take up the wear you're imparting in the chain).

A possible Poor Man's Solution would be to put in a half-link in place of a full link which would shorten the chain considerably. Normally this would be done if it was machining that created the slack, and not chain wear. If it is really chain wear, you are in some danger of having the chain break. This is pertty un-common, though possible. Depends on how much you plan on driving it, and how much time/money you want to put into it...

Matt.

I read all the posts and I do not think you are REALLY beyond the point I mentioned. I think you may need to recheck more carefully.

When things get to wierd, go back to the basics and re do them.

Rich,
Please read the entire thread again and create a check list of possible causes, then verify each has been dealt with.

The chain appears too long due to any number of reasons. Using a mechanical tensioner is not the long-term solution; getting the correct idler arm geometry is. If the mechanics of the rebuild are okay, then it's a matter of getting this area to look the way it did from the factory. The solutions are in this thread.

Let me repeat: Using a mechanical tensioner is not the long-term solution.

Sherwood Lee
http://members.rennlist.org/911pcars

I am going to replace the chain this week sometime. I need to get the parts (chains, gaskets, etc.) and the little jig to hold my dial indicator so that I can do the cam timing per J.Walker. I'll post the results of the chain replacement and see if it cures the problem. I am tempted to get new sprockets while I am in there as well.

Rich

Rich,

Step back, save your money, hit yourself in the head a few times with a monkey wrench and ask yourself, What am I missing? Throwing money at new parts, ie sprokets, is not a solution to a problem like this, its an outlet for flustration. Drink a couple of beers, take a deep breath, and say to yourself, lets look at this again, from scratch.

Did chain replacement solve the problem?
 

Hi Rich,

Sorry to revive an old thread but...

I was reading your thread on the 2.7 timing chain issue and noticed there wasn't an update when you replaced the chains. I have a similar situation with a 2.7 that had mechanical tensioners. After installing the oil fed tensioners, the left side inler arm extends to the cam housing. Thus, the chain rubs at the base of the idler arm when cold. Once the engine starts to warm it stops rubbing.

This brings up a question for the experts. In my case the engine expands significantly enough when warm, to pick up the slack in the chain, so it does not rub on the idler arm. Therefore, if the mechanical tensioner were adjusted too tight when the engine was cold, then when the engine warms the chains, cam bearings, idler arm shaft, would experience a significant load, side load etc. What type of periferal damage could have occured?

Back to Rich. Similarly, I do not know the history of my motor. Although, I can assume it had a top end rebuild because the PO attemtped to seal rocker arm shafts with high temp silicone instead of o-rings. Did the chain replacement fix the problem? Did you replace the ramps and sprockets?

Thanks for your assistance.

Jason 74 911

Jason (and others):

Sorry for not updating the board on this project lately. I ended up putting in the Porsche master link timing chains and pulling the Carrera pressure-fed tensioners from my spare 2.4 liter. Don't worry about re-timing the camshafts -- it's a piece of cake! Anyhow, I installed them about 2000 miles ago and the car has been running just fine. I have been driving it pretty hard and there has been no problem with the master link chains (I figured if Porsche supplies them they must be OK). The 2.7 liter really pulls hard in the midrange with the webers and with the light early car, it really moves. I am very happy with it.

For all of those who worry about used engines that have sat for a long time, I can say I have had very good luck with them. I bought a complete 2.0 liter out of garage where it had been sitting for six years for $800, cleaned it up, stuck it in and drove it for almost three years. As part of the mega-package, I got an old 2.2 liter engine that sat for many years. KeithO64 and I cleaned up and stuck in the chassis and it has been running strongly for many thousand miles. It runs very strong and clean up to 7000 RPM every time. I sold one other used 2.7 liter engine that I got in the package and that worked out OK as it is running somewhere up in Oregon. Once the problems were sorted out, my 2.7 is running just fine. All of these engines sat for many years, but worked just fine once they were cleaned up. If I was going to run LeMans, I would do things differently.

Anyhow, it runs fine. I have been absent for a while since I acquired a nice used 325i for a track mobile. Hopefully it is back to the Nurburgring next August!

Rich

Jason,

By mechanical tensioners, do you mean the type with a "set screw" that you adjust to obtain tension? If so, the are a Bad Idea as they will cause mega chain wear. As you noticed, things expand when hot, and the tension varies considerably with a "fixed" tensioner and causes all sorts of problems. While they may be more reliable than the factory types, the make all sorts of other parts unreliable...

Hi Matt,

Yes, I do mean the mechanical tensioners with a set screw and lock nut. I don't recall the amount of tension on the chain when the mechanical tensioners were installed but I am assuming it was tight due the amount of chain slack I have now with the carrera tensioners, on the left side when cold.

The motor runs strong so I am planning to replace the chains and ramps. However, I would like to know what type of damage could have resulted from tight timing chains and what to look for.

Thanks for your reply,

Jason