Carrera tensioner questions
 

I'm rebuilding an SC motor I got a while back that already had updated oil fed chain tensioners.

What is the purpose of what appears to be a check valve at the top? See green arrow below. What pressure should it work at? Is there a way to check or adjust it?

I can blow air into the oil feed and air easily blows out the check valve. That begs the question, how much oil is dumped out through that check valve during normal operation?

If this has been discussed already, what's the link? I searched and could not find any info.
http://forums.pelicanparts.com/uploa...1463164905.jpg
Thanks,

I forgot to mention that with only 10 psi from my compressor it blows through.

Looking at one here it looks to be a simple spring loaded ball check.
I'd think it's an air bleed-acts like yours but I do know it works fine.

It is supposedly a pressure release valve. (according to the info in Wayne's book) Yes, a check ball.

I can't believe that it should be releasing pressure at less 10 psi! So basically it is an oil leak into the chain housing? What am I missing?

Or is my tensioner shot?

Is this a viable solution? Anyone done this?http://forums.pelicanparts.com/uploa...1463239909.jpg

http://www.porscherepair.us/porsche-...e-oil-tank.jpg]

Check out Mr. Fricke's explanation in post 17. From his explanation, the pressure at which that valve releases excess oil is of little consequence as long as there is enough pressure to backfill the main chamber as needed. That's my read anyways.

Reconsider your approach after reading #13 as well. Had to chuckle at that one... You don't want to monkey with that orifice as that's how air escapes the system. You may inadvertently be putting the tensioner in failed mode from the get go.

Thanks for the link. I had acutally posted in that thread. I wasn't serious about the screw.

I think I understand the operation of the tensoners.

What I don't understand is why my tensioner's "bleed" valve, or what ever it's called, releases at 10 PSI. When I blow in compressed air it blows straight through the "bleed" valve starting at 10 PSI. Wouldn't that be the same as an oil leak?

I'm just trying to find out if this is normal or damaged. I imagine someone on this board has done this check, or is there a Porsche service bulletin covering it? I don't see anything in the workshop manual about this.
http://forums.pelicanparts.com/uploa...1463413222.jpg

The only thread I've seen about applying air pressure to test a tensioner is here. Note it also mentions the check valve opening at a fairly low PSI (14) on two brand new tensioners.

I would think a better indicator of tensioner health would be to purge the air and try to compress the piston. If you collapse the piston by hand it's probably toast. If you need a C clamp or vise to seat the grenade pin for installation, they're probably OK. As for it dumping oil, I gonna go with the thought that the designers have figured all that out. All I know is that my pressure was fine before and after I installed my Carrera tensioners.

Thanks for the link. Ironically the Rennlist discussion included a link to a Pelican thread. I didn't see it since it was written in '01!

http://forums.pelicanparts.com/porsche-911-technical-forum/55326-alert-911-carrera-chain-tensioner-installation-2.html

I still think it strange that these tensioners would bleed oil at such a low pressure. Maybe for extra oil to the chains?

The tensioner doesn't need a highly pressurized source of oil to work. The reservoir inside the tensioner is there to ensure an ample supply of oil is right there at the tensioner's inlet valve on the left side of the cross sectional view. The engine oil feed is just a "convenient" and constant source of oil to feed the tensioner, instead of the older self-contained tensioner that is common to many engines.

Think of it another way, you can "pump up" these tensioners simply by submerging them in a container of oil. So the internal workings of the tensioner takes in the oil by suction and or gravity and the pistons/orifices/whatevers inside it build the pressure. Therefore it's not necessary to have the bleed valve crack open at a high pressure.

Another thing to note too is that the tensioner bleeds itself two ways. It bleeds itself at the top of the piston (you can see the oil come out of the bleed slit when you compress the tensioner) and the reservoir "overflow" is the nipple.

I wish I had saved all of the SmartRacing stuff before they closed up shop. I always told myself, "Man, this SRP site has awesome info and instructions. I should download all these pdfs in case they close up shop someday." Sure enough, closed up shop one day with no advance notice (how dare he not notify Pelican forum! ;) ) & took down the website before I saved all the great info. Son of a bee sting....... http://forums.pelicanparts.com/uploa...1463675698.gif

My point is that they had a part/fix in their catalog for these tensioners to make a failsafe, along with instructions. Here's the parts & tools

http://forums.pelicanparts.com/uploa...1463675415.jpg

That looks to be parts for the Jerry Woods "fix" using a shim inside the main chamber. Unfortunately, Jerry's write-up was also taken down.

I still think it is counter intuitive to have pressurized oil feed in and just squirt out the relieve valve.

Maybe that is why Porsche introduced the cam oil feed restricters? To counteract the loss of oil pressure from the tensioners relieve valve?

I understand the operation of the tensioners. I have rebuilt the ones in my '71 several times. Their oil supply is limited to what was in them at the time of rebuild. So to "fix" the problem and extend the life of the tensioners Porsche started to supply them with pressurized oil. That part makes sense. I could see a relief valve opening at say 50 or 60 lbs, but 10 or 15psi? Makes no sense to me.

tharbert,

Yeah apparently Jerry Woods Enterprises and Craig Watkins/SmartRacing worked closely on a lot of things. I think that's how JWE was able to take over most of the SRP product line. Unfortunately JWE doesn't do much at all to promote that nice line of products from an internet-presence standpoint.

Trackrash,

I hear what you're saying in terms of the logic behind the oil being lost to the reservoir relief valve. But since the tensioner doesn't really need oil pump pressure to function, there's no reason to have it hold higher pressure. Not saying the 10 psi discharge is necessarily the norm. Just saying that the Carrera tensioners don't require the engine's higher system pressure to function. But I also hear what you're saying about the low cracking pressure being a detriment to the overall oil system pressure.

I don't believe Porsche introduced the cam oil feed restrictors on account of the Carrera tensioners. The smaller oil line adapter appeared in 1991, which is long after the introduction of the Carrera tensioners for the 3.2 engine.

Maybe the engine doesn't "feel" the effect of that low cracking pressure in the tensioner, on account of the tiny oil supply lines that minimize the amount of pressure loss to the overall system? Those supply lines have a really small inside diameter and choke down the amount of oil that is being delivered to the reservoir. I don't know the technical analysis of that condition. I just look at it like a garden hose with a small pinhole in it. That water the hose is spitting out the sprayer nozzle doesn't really feel the effect of the pinhole. But if you made the pinhole bigger, it'll have a greater detrimental effect on the output at the nozzle? Not sure if that's an equivalent comparison i'm making.......

Just to add... Carrera tensioners came in 84. Restrictors came in 91 originally for turbos along with an upgraded oil pump flow. The restrictor was mainly to reduce oil foaming. Good thread here...

That feed line is indeed small. Throw in that the relief orifice is probably even smaller. Couple all that with the notion that 20 wt oil's not going to come out of the relief orifice as quickly as air. A cup a minute on a system that puts out gallons a minute @ 4000 rpm is of little consequence...except that's a cup that doesn't get to the cam bearings and lobe squirters.

I agree. It seems as though the relief orifice is the real restriction. I have one tensioner that is missing the check valve. It doesn't bleed much more air than the "good" one when I put compressed air through it.

I guess in the big picture, Porsche thought that the oil leaking out of the check valve was a reasonable compromise in order to keep the tensioner's reservoir filled with oil.

Still, considering all the small details that engine builders tend to, I would have thought that someone would have played with the tensioner's relief valve in the past.

Hello
i have mechanic tesioner in work order condition (in 2,4 engine from targa 1972), but i don´t know, how old they are or how kilometers.- I buy safe collar; but i think maybe i can rebuilt them before put safe collar.- O better, i can put safe guards inside of them (than pressure - fed tensioners).- Because i read some safe collar can brakes.- You know is posible put guars in mechanic tensioners??
regards
Enzo

I buy used kit of carrera tensioners, to upgrade in my engine, but i scare they can fail (because the are used), because i prefer now (first step) put safe collars in mechanic tensioners.- How can i check the mechanic are in working condition (they are in engine)??? How can i check the pressure fed tensioners, are in working condition, they are out of engine.-

I am in Argentina and now is imposible buy in pelican parts for my car, or buy rebuilt kit for mechanic or pressure fed tensioners (custom close for parts).- I want buy o ring, in local shop; (one to one); and rebuilt mechanic or pressure fed.- Someone have measures of o ring of mechanic tesnioners to rebuit them o measure o ring of preasure tensioners.-
regards
Enzo

The relief valve setting is based on how much force Porsche wants applied to the chains by the tensioners. 10 psi x area of plunger = lbs of force applied by the plunger. Believe it or not engineers usually have a reason for their madness.

My further research on these tensioners shows that there is a restriction, much like a metering jet, to the oil flow into the supply chamber. It is seen in the diagram between the oil supply and the supply chamber. Then the oil that then flows into the supply chamber is allowed to flow out of the check valve, or relief valve, at the top. There is no more than 10 or 15lbs of oil pressure in the chamber. There is a check valve at the bottom of the plunger that allows oil into, and out of, the working chamber. The purpose of the oil supply is just to keep oil available to the plunger as needed.

Good to know, so would it be recommended to prime with oil when re-installing as not to run it dry? on initial crank of the engine or will crank only to prime the engine good enough for us with the 3.2 tensionsers?

Trackrash - yes, the orifice size is designed to supply the volume of oil needed to maintain a certain pressure in the chamber across the range of engine oil pressure from idle to redline. Less oil flows thru the supply orifice at idle than at redline because the main oil pressure varies from say 1 - 5 bar or so. The setting of the relief valve is designed to maintain a specific pressure in the chamber and against the plunger, that determines how many pounds of force the tensioner applies to the chains. A minimum is needed to maintain the chain tension req'd for correct valve timing. Too much pressure and the chains wear out sooner or something in the tensioner system breaks. Plug the relief valve orifice with the screw and see what happens when the plunger sees 4 or 5 bar of pressure. The "leak" from the relief valve is factored into the sizing of the main oil pump.

Draco - yes, I'd prime the tensioners with oil before installing.

Thank you Boosted79!

The only way I can find to bleed all the air out of the "working chamber" is to remove the piston and re-assemble the tensioner immersed in oil.

I can find no other way to bleed out the air that is in the working chamber. One of my tensioners was spongy. It had air in the working chamber.

So if your tensioner's piston feels spongy when you depress it by hand then I would recomend removing the piston and filling it with oil while immersed in an oil bath. Note: Porsche says, in the manual, to replace it if it is not firm.

If there is another way to do it, I would like to know.

BTW, WTF is the "orifice" pointed out in the diagram? My tensioners don't have any orifice on the top of the piston, that I can detect.http://forums.pelicanparts.com/uploa...1465090459.jpg

Edit: I was unable to blow air through the piston and have it escape from the plug orifice. However when using a C-clamp to compress the piston, I did notice some oil escaping from the plug orifice.
Interesting that air does not enter the chamber when the piston is allowed to extend. See post #33 to see how it looks internally.

Update, as Boosted79 suggested, I primed the tensioners before install using a cheap HF old skool oil can full of DELO 400 15W40. Yes, air and bubbles spewed out under the can's hand squeeze pressure.

Then after install I did it couple more times until all air bubbles were gone.

In retrospect, I should have fill the cam oil lines to help reduce air into the tensioners upon cranking. Oh well, no harm.

I hand cranked it several times then starter cranked with out fuel or spark 10-12 times to insure to purge the lines of oil to the tensioners. (after reading some posts, not sure if this really had enough pressure to push oil into them but it seemed to have worked or I got really lucky )

I did check the tensioners to insure the ball at the relief valve were in place, CHECK.

One thing I do want to note was I slowly pressed the tensioner to use the lock pin, after watching Nick Fulljames warned about doing it too quickly which may damage the inner seal.

Started the car and ran for 20 minutes and used stethescope to listen to the chains, QUIET, CHECK.

It's a pretty simple mod to make Carrera tensioners failproof, look at post #43 of this thread. This is also called the Jerry Woods mod.
http://forums.pelicanparts.com/porsche-911-technical-forum/199819-shops-dont-recommend-carrera-tensioner-update-3.html

Looking at the kit you posted I'm not sure what the little shafts do, the tubing is the lock and I bet it's short (to work as a fits all kit) so the washer looking things are shims.
The tools I'm not sure but likely they are for measuring and/or installing.

The only thing about the mod is you can't use the grenade pin for install and you lose the C-clip, so care must be taken when the tensioner is removed.
You can't fully depress the tensioner for installing, so you will need a C shaped tool to hold it the together as you slip the tensioner in place.
But it does make the Carrera tensioner failproof so it's worth the hassle.

The problem I have with one of mine, is there is air in the working chamber. I have not been able to get the air out of the working chamber by supplying oil to the Supply chamber.

The only way I can see to get the air out of the working chamber is to remove the piston, immerse the whole unit in an oil filled container, make sure the air is out of the piston and the working chamber, then re-assemble.

When I compressed mine, oil would bleed out around the piston.

These tensioners don't have internal O rings or seals, to my knowledge.

You would think that Porsche would have, at some point, published a service bulletin on maintaining or repairing these tensioners, but I have not been able to find one.

AFAIK, there is no rebuild kit nor any repair instructions for these but then again, they weren't always this expensive. The kits are now about $400 more than when I bought mine: $1088. There's probably not enough in it for some entrepreneur to backward engineer one and come up with a rebuild kit. I would think the challenge would be to find the failure point when they go bad.

Strange, but I felt resistance like liquid pressure not mechanical like from a spring. Well in any case I took the precautions with a slow compression of them, seem to work.

Out the piston? Hmm, mine did not do that for sure, the oil came out the inlet and some from relief valve.

Could your tensioners have been replaced in the past? Mine looked pretty original and tired but no apparent leaks from the cylinder itself that I could observe.

I totally agree. Seems to me that the check valve would be the main concern.

The tensioners I have are on a '78SC motor. So obviously not original, and I have no history on the motor. FWIW one of my tensioners is spongy. So there was air in the working chamber. I want to find out why this occurred. Problem is, no one seems to know exactly how they work.

My next step is to bleed, test, and compare to my good tensioner. I have taken it apart and see no obvious problem. The check valve seems to work, the spring is good, and I don't see any abnormal wear. (the relief valve up on top is loose, but I'm not sure that is the cause, IMO.)

From this thread. http://forums.pelicanparts.com/911-engine-rebuilding-forum/902416-never-ending-problem-13th-engine-rebuild-very-long-post-6.html#post9218535

This sounds like good advise.

I've never primed mine.

The pressure on the chain to keep the slack part fairly taught so it doesn't jump around too much is mainly from the spring inside. The oil below the piston acts like the oil in a shock absorber, dampening out the oscillations. And it self adjusts for dimensional changes due to wear and thermal effects. The older ones essentially had one way valves allowing the splash oil which gathered on their cup-like tops (very pronounced in the really early ones, but same effect on the later ones)to be drawn into the chamber below the piston as the piston rose up, which then retarded its being pushed back down. More slack, more oil and a higher piston level at which this effect began.

The pressure feds just provide a more consistent source of oil for this purpose. There is a theory that these were a solution to a problem already solved - that the early tensioners failed because the idler shaft bushing was not wide enough, which was changed somewhere before the advent of the pressure feds - first I think on the Turbos. So those engines don't need the pressure feds. But we all religiously installed the pressure feds on our engines if they didn't have them. By now, the advice is that you must upgrade the idlers while installing pressure feds on early engines.

Time for a follow up.
According to the manual, if the piston moves easily, the tensioner is faulty and should be replaced.
http://forums.pelicanparts.com/uploa...1469979404.jpg
I have added two labels to the diagram from the manual.
http://forums.pelicanparts.com/uploa...1469979498.jpg

I have a tensioner that felt like it had some air in the working chamber. It would depress easily for the first few mm when I pressed on it with my finger before becoming firm.
To bleed the air out, I forced oil into the supply chamber with an oil can until oil came out the bleed valve.
I then used a clamp to compress the plunger while the tensioner was held upright in my vice. I noticed some oil escaping from the plug (orifice) while doing this. I repeated this a second time. The tensioner's piston was then firm the entire length of it's stroke.

As a note, I tried to bleed the tensioner upside down. This only made it worse, as more air entered the working chamber.
I also tried to compress the plunger, upside down, and release it submerged in oil. This also did not work.
In conclusion, if the supply chamber is full, and you operate the plunger with the tensioner upright, you should be good to go.

Edit: I made an edit to post #23.

Here is what the plug (orifice) looks like removed. I pounded it out with a punch. It appears to be 7mm threads. Apparently it does allow air and some oil to escape. I had one tensioner that I could not bleed the air out of by compressing the piston repeadly. It remained spongy and could be compressed by hand.
I removed the plug and cleaned the plug's threads. Now that tensioner is solid after I bled it.
http://forums.pelicanparts.com/uploa...1470427079.jpg

Nice :D

Gordon - this is the first picture/diagram I have seen of this part. I supposed it was two pieces (the top looks like it is harder steel, as befits a wear surface). And that it was somehow held in.

I knew that it functioned as a slow, high pressure, bleed, because when compressing an oil filed tensioner in a vice so you can insert the pin you see oil coming out, so need a rag under the vice. Makes sense, as this would quickly bleed any air out as well.

I take it that when you pounded one of these out with a punch that damaged internal and external threads? But that on another one you found a way to unscrew it? Small pipe wrench?

Amazing that the passage way is the threads, though.

just crazy.

The plug appeared to be one piece. There were no threads in the piston. The plug is a press fit. I used a drift punch to drive it out, then I used my vice to press it back in. It is a tight fit.

The oil or air will follow the threads around the screw then out the top. So it acts like a restricter.

And...

One of my bleed valves seemed slightly loose. It functioned, but I have heard of them falling off. So I took the precaution of safety wiring it.

http://forums.pelicanparts.com/uploa...1470526077.jpg

What a great idea. I accidently knocked one loose once, prying around with a screw driver trying to do something. I pushed it back in, and crossed my fingers. Eventually it popped off. I got a replacement from a trashed tensioner. They are held in only with the sharp ends of the three or four "legs" of the cap shoved into the hole - not much, you'd think, but obviously enough if undisturbed. I took a little dremmel diamond coated round blade and cut a slot on the ID of the hole, so the legs had something to grip other than just a cylinder - this seems to have worked, but your idea looks simpler, and maybe more positive.

Critical test........
 

Gordon, Walt, et al.....

After priming a Carrera hydraulic tensioner/s multiple times, would you be able to push the piston in 1/3" by hand (without mechanical device) before it becomes very stiff? I am trying to find out how to test or evaluate a good one from a failed tensioner. Since you are doing a good job in discussing the operation and function of the tensioner and its components, it would be prudent also to determine a simple test.

If we could determine what pressure or force applied to the piston (primed) that it is good or failed would be a good stepping stone. And this could be achieved by a collaborative work by several interested parties. Using adjectives to describe how hard or soft the tensioner is very subjective. If we could use an arbitrary numbers (lb. force) would be ideal. Thanks.

Tony

What about just going to soloid tensioners like they sell at JB racing?