Manual Cam Chain Tensioner

[cabriobrad]

I have no idea where these come from, but correct me if I am wrong in thinking that these are what I think they are. I ordered some of the safety collars from our host, and now realize I can't use them...true?

Are there any instructions anywhere on how to set these since I am in here already?

Thanks in advance
Brad

[Peter Zimmermann]

Those are JUNK, get them out of there! They stretch chains and can cause serious problems. This is a perfect example of the aftermarket that I absolutely despise. Chains are designed to expand/contract 2mm with temperature change. A mechanical tensioner cannot cope with that, and is either too loose or too tight at one or the other temperature extremes.

[cabriobrad]

Hey don't mince your words...tell me how you really feel.(joking)

I can't see them being that bad, they seem to be working fine now...any other opinions?

I had an APE(i think) manual cam chain adjuster on my gsxr750, and never had a problem in >30,000km. Now, if that's not high reving high perfomance engine, I don't know what would be.

[fitchn]

Porsche used mechanical type chain tensioners in their race cars in the 70's and some 911 owners that I know run them on their street cars. I've never heard of a problem but others on this board certainly may have. I certainly don't have enough data points to come to any serious conclusions.

I would imagine the initial setting of the chain tension may be tricky, and yes of course the tension would change slightly with thermal expansion, though whether the tension would increase or decrease would depend on the materials involved.

I imagine the chain is made of steel, which has a thermal expansion coefficient around 7.3 microinches/(inch*degF). In an extreme case the temperature of the chain may change from 0 to 225 degrees Fahrenheit. Assuming that the chain is around 3 ft long (that's a guess), that's 36 inches so the length would increase by... about 60 mils (thousandths of an inch). That's right around 1.5mm, close to the number quoted above.

At the same time that the chain lengthens, so does the tensioner. Assuming it is also entirely made of steel and starts with a length of 4 inches (guess again), it will increase in length by about 7 mils over the same temperature change as above. That of course isn't as much as the chain length but that really isn't important. You actually do worse than The tensioner length increasing changes the path length that the chain must travel. A couple of triangles later (4, 2 for each tensioner), the path length increases roughly by about 14 microinches. Significantly less than the chain expansion. So the chain gets stretched by roughly 60 mils if it was set perfectly tight at the 0 degrees Fahrenheit condition, though I wouldn't be in the garage if it was that cold.

If your tensioners are made of aluminum you do a little better as the expansion coefficient is around 12.3 (>7.3). In that case the chain path length increases by about 40 microinches, still not nearly enough to make up for the change in chain length.

So I guess it all comes down to whether you are OK with your chain stretching a bit, though figuring out just how much a chain can stretch before you skip timing and blow up the motor is an expensive experiment. Cheers, Noah.

[aadrew10]

That's like using duct tape to secure the valve covers. 100% gangster ****.

If I were you, I would order some real chain tensioners, and then install them. How many miles have you done with that motor?

[aigel]

Noah,

Indeed, that's not an uncommon tensioner on a race car that is opened up every 20-50 hours run time. This allows for adjustments. Also, a race car generally isn't run from a cold start in the middle of freezing winters (something a daily driver needs to be able to do)

Your math on the steel expansion is good, but the sprockets don't stay at the same distance from each other through temperature changes. They are connected by a mass of aluminum (cam housing, cylinders, case). Al's CTE is almost twice that of steel. The chain will actually tighten with higher temps.

At any rate, that thing would not stay in my road driven car. I would put it on a hot rod engine that I pull apart every 30 hours without worry though.

George

[Flieger]

Your chain might be ok with mechanical tensioners but your intermediate shaft will crack, and the case can become junk as the bearings wear oval shaped. If the intermediate shaft breaks, the valves hit the pistons and the engine is completely junk.

Just as this guy. He might have some tensioners for you for real cheap.

Timing chain and tensioner issues

[slodave]

Originally Posted by aigel

noah,

indeed, that's not an uncommon tensioner on a race car that is opened up every 20-50 hours run time. This allows for adjustments. Also, a race car generally isn't run from a cold start in the middle of freezing winters (something a daily driver needs to be able to do)

your math on the steel expansion is good, but the sprockets don't stay at the same distance from each other through temperature changes. They are connected by a mass of aluminum (cam housing, cylinders, case). Al's cte is almost twice that of steel. The chain will actually tighten with higher temps.

At any rate, that thing would not stay in my road driven car. I would put it on a hot rod engine that i pull apart every 30 hours without worry though.

George

+1

[fitchn]

George,

I was not implying that just because Porsche used it in their race cars it was appropriate for the street. Certainly in a race motor you have frequent access to the cam sprockets and could make adjustments accordingly (though after seeing the destroyed intermediate shafts and case in the linked thread above I would say you would still have to be extremely careful that you were setting the tension correctly).

I had not considered the sprocket movement due to the case/intermediate shaft expansion, thanks. The point of my rough calculation was not to convince the OP that everything was OK, but that it would be impossible to have a mechanical tensioner maintain the same chain tension over a broad temperature range. Looks like I oversimplified things a bit though.

Another hint would be the following: if it were as simple as putting in a mechanical tensioner, Porsche would not have bothered with the pressure fed tensioner upgrade (carrerra), or even the spring loaded versions that predated them. I'm not saying Porsche doesn't make mistakes in design (not by any stretch of the imagination), but if the solution were that simple I think they would have applied it.

[cabriobrad]

Thanks to a fellow Pelican, I have purchased a set of hydraulics for the car, that and the safety collars, although not oil feed upgrades, should be better than what I have..yes?

p.s. thanks mcfoo!!!

[304065]

I bet if you look closely you will see the words "Pacific Design" on those tensioners.

They are great for setting cam timing, however! Someone will buy them.

You might take the opportunity to evaluate your chains and sprockets. You have the old SWB type sprockets with the pointed teeth, the new ones have square teeth. No big difference as long as the teeth aren't worn.

[daniel911T]

I realize that you have already made the decision to go to some form of stock tensioners (it sounds like the spring loaded type), but as someone who had a motor destroyed by a set of mechanical tensioners, I think you NEED to do a thorough inspection deeper in your engine.

I know this link has already been given here, but I think it bears repeating, and will be especially relevant to you:
Timing chain and tensioner issues The last few posts will be especially useful.

Take off the sump plate, get a very powerful flashlight, and do a thorough inspection of your intermediate shaft, including grabbing it and checking to see if it moves at all left to right. There shouldn't be any play at all in the intermediate shaft, if it wiggles at all, then you have a serious problem. While you're down there with a flashlight, look toward the back of the engine (toward the timing chains) and inspect the intermediate shaft hole in the case, (it should be round.) Also, give the motor a bit of time to leak out all it's oil, then reach your fingers up into the bottom of the case and feel for any debris. While you're at it, also check in the bottom of the chain housings for debris, and check the tensioner bases for damage (see the picture in the above link.) Finally, while you've got the chain covers open, take a good hard look at the intermediate shaft drive gear, visible from the starboard (passenger side) chain box, and take a careful look for any damage to the teeth. If you find any of these indications, your chains have probably pulled the intermediate shaft crooked and messed up the case.

I sincerely hope that your engine has avoided the fate that mine suffered.

Best of luck, and please let us know how it goes!

Dan

[Peter Zimmermann]

...and don't forget to replace the six chain guides, aka ramps.

[daniel911T]

Originally Posted by peter zimmermann

...and don't forget to replace the six chain guides, aka ramps.

+1!

[GH85Carrera]

Originally Posted by cabriobrad

Hey don't mince your words...tell me how you really feel.(joking)

I can't see them being that bad, they seem to be working fine now...any other opinions?

I had an APE(i think) manual cam chain adjuster on my gsxr750, and never had a problem in >30,000km. Now, if that's not high reving high perfomance engine, I don't know what would be.

Peter Zimmerman is a voice of experience and reason. It's your engine and no one but you cares how much you spend on it. I learned a LONG time ago to seek out the voice of knowledgeable experts and follow their advice. I would love to hear Grady Clay's opinion of those adjusters. I suspect it would match Peter's.

[andrew15]

Hey Brad - I've got a pair of 930 spring type tensioners heading your way in the box with the valve covers, etc

AM

[cabriobrad]

andrew15...you are a man among men...this guy gets a +100!!!!!

Chain ramps...would that be this kit??

Pelican Parts - Product Information: C-105-22-KTN

[Scott R]

Side note on the safety collars, don't use them. I have a 3.0l torn down that's now a complete loss thanks to them. As the tensioner failed the chain chewed through the collar and it separated from the tension rod. There is now aluminum pieces all though the case oiling system. Damage to the chain box where it flew around, and damage to the lower case as it bounced around in there as well.

[aigel]

There are several items than need to be done to make this fail safe:

- Carrera chain tensioners
- Later - wide base - idler pulley arm
- Modify tensioner pistons with internal crash collar / a-la Jerry Woods

Everything else is a patch / unsure solution. JMHO.

George

[TTSam]

Is there a specific noise if the tension is not right?

My 993 turbo 1996 is making a clicking noise that sounds like the left chain is tapping ATALAH something.