Carrera tensioner questions

[Trackrash]

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.

Thanks,

[Trackrash]

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

[prschmn]

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.

[Trackrash]

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?

[tharbert]

]

[tharbert]

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.

[Trackrash]

Originally Posted by tharbert

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.

[tharbert]

Originally Posted by Trackrash

I'm just trying to find out if this is normal or damaged...

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.

[Trackrash]

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!

Alert - 911 Carrera Chain Tensioner Installation!!!

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

[KTL]

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.......

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

[tharbert]

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.

[Trackrash]

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.

[KTL]

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.......

[tharbert]

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.

[Trackrash]

Originally Posted by tharbert

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.

[enzo777]

Hello
i have mechanic tesioner in work order condition (in 2,4 engine from targa 1972), but i donīt 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

[enzo777]

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

[boosted79]

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.

[Trackrash]

Originally Posted by boosted79

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.

[DRACO A5OG]

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?