My experience is, after bleeding the tensioner as I outlined previously, the piston is stiff the entire stroke. I could not depress it with my hand. I used a c-clamp and then it went in slowly.

Hopefully others will chime in. It would be great if more info on these tentioners could be documented.

So when you punched it out it wasn't really threads but a ribbed affair just to make a slight controlled leak?
I'm kind of thinking there's not much to rebuild, clean them with something like MEK, pop out the contact pad, clean replace and they should pump up.
The safety wire is a good idea.

Then add in the Jerry Woods mod and and it should be a failsafe set up.

Let's think of what failure modes might be?
1) the external pressure relief fails, like it is dislodged. That means that the tensioner does not have the benefit of more than the suction of the piston to get replacement oil into the cylinder. This is the only one I have experienced, and it is also the most obvious.
2) the internal check valve fails. That means the piston just pushes the oil in the cylinder back out, so little or no damping.
3) there is wear between piston and cylinder. There are no rings, O or steel, to prevent oil under pressure from doing this once the clearance gets too large somehow. Might this be the most common? Could you tell because after filling things you could compress by hand or at least more easily than with a vice or C clamp, and you could see the oil coming out around the piston, and not out at the tip?
4) an obstruction, either in the feed line or in an internal passage? But how would this happen, since engine oil is filtered, and if there is a bunch of debris in it a failed tensioner may be the least of the problems?

5) what if the threaded passage from the cylinder out the tip, whose design Gordon has uncovered to explain its observed function, were clogged? If so, air in the cylinder might find it hard to escape. That could account, for instance, for a tensioner which will compress more easily part way, and then stiffen to where hand pressure is inadequate?

6) there must be other possibilities.

It might be a bit tricky to come up with a test. You would want to know how many pounds of force would be needed to depress the piston X amount in Y time. You could insert a small load cell (like the inexpensive hydraulic gauges you can use for testing valve springs)into your vice or clamping device, and see at what force you first saw a droplet of oil coming out of the tip? Borrow a shock dyno with some kind of adapter? The tensioner is a whole lot like a coilover shock strut, but with only a single compression value on the shock, and tuned to deal with whatever frequency range chains vibrate at.

Yes, a spiral groove around the plug is more of an accurate discription. It just happens to match a 7mm screw, with the threads ground down.

In my case, the spiral groove had some crud in it effectively blocking the "orifice" which in turn prevented the air to bleed out. I removed the plug, wire brushed the spiral grooves, and replace it. The tensioner then bled out the air and seems to be working correctly now.

Seems to me that the only other point of falure would be the check valve. As you say some MEK should take care of it.

As a note. I was going to do the Jerry Woods mod. But on my initial test fit-up there isn't room for it. I only have about 1/4" of piston travel in the tensioner with my new chains. I will have to varify that once my new cams arrive.

I think the function of the external pressure relief is up for debate. From what I can tell, by blowing air through from the oil fitting, the restriction to oil flow is inside the tensioner. If you look at my previous post, I labeled a restriction orifice just inside the oil supply fitting.

I could not tell the difference, when blowing air through, when the pressure relief valve was present or missing. I compared my good tensioner to my failed one, which had the relief valve off.

I am guessing it's function is to prevent air from entering the supply chamber after the motor is shut down.

The only way to know for sure, I'm guessing, is to put pressurized oil through one with some gauges hooked up.

That's an interesting idea. It would explain its flimsy attachment, and small spring.

The check valve inside the base of the cylinder, which is similar, would never have to rely on the spring or its retention to hold any pressure, because the just a little pressure from below - the pressure line supply side from the adjacent chamber - would let oil flow into whatever space there might be for it just below the piston.

The piston trying to push down would produce quite a bit of pressure (for instance, when clamping to bleed), but that pressure would all be pushing the ball into its seat, with the spring just holding it in position when there isn't such pressure.

So if the orifice for the external check valve is so small that it delivers little force or flow upward, it wouldn't need to be sturdy in that direction. And no amount of atmospheric pressure with a vacuum in the supply chamber would cause problems.

As I understand it, Porsche didn't want to have engine oil pressure pushing the tensioner piston upward. That's not how shock absorbers work. But the tensioners don't have the wonderful seals shocks have, so just keeping oil handy to replace that which worked its way out was all that was needed?

"As I understand it, Porsche didn't want to have engine oil pressure pushing the tensioner piston upward."
Yes, it limits the PSI that the tensioner piston sees to the setting of the relief. PSI x piston area = force applied to tensioner arm adjusted for geometry of the arm = force appled to the chain.

Well, the conventional wisdom is that the spring inside the tensioner is what does the tensioning, All it has to do is to keep slack from accumulating between the cam and IS gears, as the slack side of the chain is never called upon to move anything while driving. So you don't need a particularly stiff spring to do that. But with just a spring the slack part oscillates. Those who have watched a running engine with a chain box cover off say it moves around rather a lot. Hence the tensioners acting like a damper/shock absorber. Shocks don't exert the kind of force a spring does. All that is needed by way of oil is to be sure the working cylinder always is full of oil. The earliest accomplished this with oil gathered in a cup on top of the tensioner, which flowed (via a one way valve, if I remember the diagrams of parts I don't use) into the pressure chamber whenever it needed to be topped up, so to speak.

Each time the chain depresses the piston, some oil is squeezed out. As soon as the chain moves upward in its oscillation, the piston raises and the cylinder needs to have some more oil. So the pressure fed system is just a way of doing this filling, and it may do it mainly by having the initial chamber, right next to the cylinder, full at all times, so atmospheric pressure (or, if you will, suction) will draw the needed oil from it into the cylinder.

Second set of Carrera hydraulic tensioners.........
 

Gordon & Walt,

I returned a brand new set of Carrera hydraulic tensioners to PP and got a replacement set. The newer set is now being primed with oil and will be installed in the engine. I could not get the tensioners to get firmer. I could still compress the plunger down with my bare hands considering that I am not that strong (old and weak).

PP says they don't have any problem/s with these hydraulic tensioners. So I am wondering if I am doing the correct way to prime the new tensioners. In the past, I just hooked up the oil lines and ran the engine. The tensioners in my '78 SC are more than 20 years old and working.

Any tip or suggestion highly appreciated. Thanks.

Tony

From what I know, you were correct to return them.

Let us know if the replacements firm up.

Tony - like you, I have just installed the few new ones I have used and run the engine. They come compressed with that pin holding them, and I never saw any reason to remove the pin until installed after the cams were timed. The ones I have removed when rebuilding my engines are sure hard to compress to reinsert a pin - needs a vice, cranked closed slowly.

So this hand compression baffles me.

^^^ My experience is same as Walt's above. I've only done a few Carrera tensioner installations a long time ago. But the same stiffness was experienced. Needed a giant set of channel lock pliers or the bench vise to compress them.

Maybe the issue with the new tensioners is pulling the pin before installation with no oil in the supply chamber?

Third time........
 

Gordon,

I was successful in getting the new hydraulic tensioners to get firm up and hard to compress by using the method you and JW suggested. But using the submerge method was not successful. The oil seems not to be filling up the two chambers by gravity flow while these new hydraulic tensioners are submerged in oil. The slight pressure exerted by the oil hand pump does the trick of filling the 2 chambers and expelled the air out of the system.

So what part of the hydraulic tensioner is causing the failure mode (spongy and soft to compress)?

Tony

The spongy plunger is due to air in the plunger.

IF there is oil in the supply chamber AND the check valve is working properly AND the plug orifice is not plugged up there should be a firm plunger.

The question is, are the new tensioners shipped with oil in the supply chamber?

^^This^^

New tensioners upon arrival........
 

Gordon,

The six (6) hydraulic tensioners I received from Sebro were compressed (pin installed) and not filled with oil. The first four (4) failed the tests due to failure to purge the air and filled the chambers with oil. However, the last 2 tensioners were done differently using your recommended method of injecting the oil. And the new tensioners were hard as rock. Thanks to JW and you for bringing up the procedure. The gravity flow of filling the new tensioners with oil while submerged in oil does not work very well compared to the oil hand pump method for these brand new tensioners.

Tony

So it sounds like those of us who have just put in new tensioners, pulled the pin, buttoned up the engine, and fired it up have avoided worrying? Because the pressure feed lines did their thing within a few revolutions? Especially if the practice is to pull the plugs and use the starter to turn the engine until there is some oil pressure?

I'm thinking that if you pull the pin after the tensioner is in the motor that the plunger wont extend to the point of allowing air past the check valve. Perhaps there is some oil in the supply chamber to start with. But if you pull the pin before installing the tensioner you get air in the plunger when it fully extends?
I wonder how many people check if their new tensioners are firm after installing them?

I don't know, but not me. What does extension have to do with the check valve? That would be the one between the supply chamber and the piston chamber - the one which won't allow oil to flow back into the supply chamber when the piston is depressed by some waggling of the chain.
Air in the piston chamber, one supposes, is quickly forced out along the threads of the piston tip, to be replaced by the much more viscous oil.

What I was trying to say was, if there is insufficient oil in the supply chamber when you release the pin, air could get into the working chamber. This is probably more likely with the tensioner out of the motor.

Air should escape from the orifice when the plunger is compressed. If there is a supply of oil in the supply chamber it will fill the working chamber when released again.

I am guessing the bottom line is, when a new tensioner is installed there is probably enough oil in the working chamber to allow correct operation with the plunger at the installed position.

This must be the case, since there are few reported failures? Most people don't bleed them before installing?

Porsche shows how to test an installed tensioner, see post #32. But there is no mention of performing this test on new tensioners.

Carrera tensioners......
 

Walt,

I've been installing Carrera tensioners without oil and primed them by cranking the engine several times. This procedure is good if the tensioners are good. But what happens when you installed defective or collapsed hydraulic tensioners in your newly rebuilt motor? Like in my case, I used the hydraulic tensioners that were defective and caused the cam timing to move.

For me, it would be a piece of mind to install tested tensioners in your engine. Rather than find them later to be no good. Thus priming the tensioners before installation is a prudent course of action. But if you know that your old tensioners are good, priming it in situ is what I would do.

Tony

Post mortem report
 

OK, time to update with new data.

Long story short, the tensioner that I had "repaired" failed after 150 miles. When I put it in the motor the tensioner was firm after I bled it. Suddenly after about 150 miles in my new motor a noise started that sounded like a bad bearing in the alternator. It was only present at around 2500 RPM, not at idle or at higher speeds. However, when I listened to the motor in my garage it was evident that it was the chain on the right side of the motor. When I pulled the chain cover off the tensioner was COMPLETELY collapsed! BTW there was oil coming from the supply line to the tensioner.

The ironic thing is, after I removed the tensioner, and when I pushed the piston down all the way and let it spring back up, it was again firm. So why didn't it stay firm in the motor? A good question.

So, I decided to test the repaired check valve using a syringe. It was not working. A new tensioner's check valve would not open with the pressure from the syringe. The old tensioner's check valve would pass air when I worked the syringe. I don't know why this would cause air under the piston, but what do I know.
http://forums.pelicanparts.com/uploa...1489210841.jpg

Geez, what a night mare :-( sorry to read your troubles Brother.

Not really a huge deal. More like teething problems for a new motor. No damage was done. A couple of hours to R&R, then back on the road to finish the break in.:p

I'm glad to share so others may gain some knowledge.

I should also mention that my new tensioner required bleeding.

I pumped the supply chamber full of oil, installed the new tensioner, pulled the pin and low and behold it was SPONGY.:mad:

I removed it and pushed the piston down using a clamp. It seemed noticeably more difficult to compress than my older one. It was firm all the way down.

Once I re-installed it and pulled the pin it was very firm.

These things clearly are poltergeist prone. For instance, how could a new tensioner be spongy when installed, but after pulling it back out, it is firm and needs a vice to push the plunger back down?

It might go like this - the new tensioner has no oil in the working chamber. Pumping the supply chamber might not cause any oil to get into the working chamber, and that is at its smallest anyway, because the pin has the piston all the way down.. Pull the pin, and whatever air was in there is still there, and the piston doesn't come up farther than "normal". So it feels spongy? Then pull the unit. Piston fully extends, and the vacuum created by that pulls more oil out of the supply chamber. A little work with the vice pushes the air out, and bingo?

Of course, if as part of prefilling you had the pin out, and did a couple of fill and compress in the vice and let it back out cycles, you'd think that would have everything ready to go - so the sponginess would be really hard to explain. But my take is that it is the piston moving up which does most of the work drawing oil into the working chamber. The pressure line just makes sure the supply chamber is full.

Though that theory does not explain why, if the exterior relief valve is removed or fails, the tensioner goes bad, because the suction part is still there, and the supply chamber is still going to be full, it will just squirt a lot of oil out. Probably not enough to drop the overall pressure, as that is a small line, but not good. However, it seems that without the valve the tensioner does not perform as it should despite the fact that the older Turbo style tensioners, which are splash and suction fed basically, seem to work well.

If I had more time, and was real brave (and perhaps foolish), I would try to get the exterior relief valve to work like the new one did. Then re-install that tensioner and see if that was the problem. Not going to happen, why take the chance?

Still you would think logically that a weak relief valve wouldn't cause the tensioner to go soft. Perhaps that tensioner had some wear in areas that were not evident, which caused it to not be up to the extra force of race springs and cams?

Experimenting would be hard. Both the one way valves are pretty simple - a ball bearing with a suitably dimensioned round seat, held into the seat by a small spring, with the spring held in place by a formed metal cap, which in turn is held in place only by the friction of the sharp edges (three of them, or is it four) of the cap. I am fairly confident that by grinding a relief in the hole(s) the cap is forced into, one can improve the purchase of the ends of the cap, and thus reinstall one which has come out. I think both of these valves use identical pieces, though I didn't think to do side by side comparisons.

The exterior one uses the spring pressure to limit the pressure inside the supply chamber. The interior one is pressed into its seat when the piston tries to move downward due to the slack side of the chain tightening, so that is a pretty positive seal.

Thinking about it, I suppose that having the interior relief pushed down by its small spring is not affected by the fact that it is (or may be) the same spring as the exterior relief, because the upward movement of the piston (which is the only time new oil is going to be admitted into the working chamber) creates a reduced pressure, so the differential is enough that the valve opens.

Or perhaps this answers my question - the suction alone may not be enough to draw unpressurized oil from the supply chamber past the spring loaded ball in the working chamber?

I suppose an enterprising person could get a longer banjo bolt for the feed line to the tensioner, and stack a second banjo on it, and attach a pressure gauge to it, and see how that pressure compared with the overall engine oil pressure, which is measured quite close to where the tensioner line attaches. Or did I forget you measured with just a tensioner what the cracking pressure of the external relief was?

However, the resistance of the cam to turning from springs is only (or just mostly?) going to affect the side of the chain which is not on the idler - that is what pulls the cam around. The idler is just there to take up the slack on its untensioned side, and my understanding is that the tensioner's role (in addition to keeping the chain being at a suitable angle where it goes onto or leaves a gear on the slack side)is to control the forces that the harmonics of the system create by causing waves moving the chain up and down on that side. I can see how spring pressure, as well as total lift, ramp angles, lobe angle, and durations, along with RPM, could affect those harmonic waves. Would they affect the amplitude as well as the frequencies?

My pressure feds have worked just as well on my "unlimited" race motors spun to 8,000 rom with both stock and later stiffer springs, and my stock 2.7 and 3.0 spun to 7,000 (lately reduced to 6,700).

If anyone has a pressure fed they don't trust and are going to throw away, I'd pay the shipping to get it just so I could harvest the two ball, spring, and cap valves. I mangled the interior one disassembling a tensioner (which I did just to see how it worked), and you can't buy these parts. I want to get the one I have back to working in my spares box.

Yes, I did measure the pressure needed to open the relief valve. Something between 5 and 10 PSI.

When I replaced the broken relief valve on my tensioner, I did not check its functioning at that time. The only test I did was to blow compressed air in and it came out of the valve like my good tensioner. Only after I removed it did I check its function using a syringe. At that point, the repaired relief valve did not really work. The syringe would easily pump air both directions through the valve. This was not possible with the new replacement tensioner.

The question is, was that the cause of the failure?

I will say this about my cam and race spring set up. I had to use a lot of torque on my cam holding tool to take the slack out of the chain to allow the idler arm to clear the tensioner when I re-installed it.

best way to prime and check is to install tensioner in engine, then pressure feed it with oil from an old fashioned oil can. A few pumps until oil comes out of top nipple then check for firmness. Submerge in oil and hand bleed never worked for me

I posted an experience years ago when installing pressure-fed tensioners. After installation, one of the tensioners wouldn't pressurize during engine cranking. I disconnected the feed line and confirmed oil pressure was available at the end of the thin supply line.

I then removed the tensioner and sporadically injected high-pressure air into the inlet port. After a few injections, I heard a click. The fluid path was restored and the piston reacted with tension.

I theorized the click I heard was the check valve at the bottom of the piston cylinder was stuck closed, then dislodged by the air pressure. This opened the passage between the supply and working chambers. The tensioners were fine up to the time I sold the engine - about 25K miles.

I couldn't find the link, but recall Bruce Anderson (or ?) describing how the tensioner works. It's similar to the operation of hydraulic valve lifters on domestic OHV engines. Each valve lifter (one per cam lobe) receives engine oil pressure to fill the lifter housing/oil chamber which causes the lifter piston to close up clearance in the valve train. During engine operation, pressurized oil bleeds out of the lifter (between piston and chamber wall) at a controlled rate to prevent over lifting the valve. At rest, a check valve closes under valve train tension thus preventing excessive clearance between valve train parts.

It's the same with Porsche pressure-fed tensioners. With the engine OFF, chain tension is greater than chamber pressure. This closes the check valve to retain sufficient oil/oil pressure to keep the chain taut. A pressure relief ball valve (top, next plug) also bleeds off excess pressure from the supply chamber.

http://forums.pelicanparts.com/uploa...1505772552.jpg

That's my read which touches on the observations and comments made in this thread.

Here's a Wikipedia description of the process:
https://en.wikipedia.org/wiki/Hydraulic_tappet

Sherwood

Sherwood - interesting conjecture, but hydraulic lifters don't have a stiff spring inside, do they? Everything I have read says that it is the spring which applies the tension on the chain (indirectly, of course), and the oil acts in the same way a shock absorber does to control what otherwise would be uncontrolled oscillation of the chain.

The check valve is a one way valve - oil under not very much pressure (it is a small spring)can enter the working chamber, but none can go the other way. Of course, if the working chamber is full, and the other check valve (whose small spring is all that opposes oil getting right back out from the supply chamber)is working, there will be no positive pressure differential between supply and working chambers, and no oil flow into the working chamber.

Given the low pressure in the supply chamber, it is only when the piston rises, creating more room, if you will, for oil in the working chamber, that oil flows into the working chamber.

And it is the bleed screw (plug) which allows "extra" counter pressure from the chain to cause some of that oil to bleed out slowly so excess pressure does not build up. After all, the idler sprocket only works on the non-working part of the chain, where it is returning from the cam gear to the IS gear, and all that is needed there is to keep slack from developing.

Walt,
True, hydraulic lifters don't use a spring. However, both work on the same principle of captured oil under pressure. During operation, the tensioner piston must be able to travel upward or downward to maintain constant chain tension under various operation conditions, engine speed and temperature. When the piston goes downward, the check valve at the bottom closes , and since fluid cannot compress, there must be a method to bleed excess oil out of the working chamber. Excess oil must exit via the piston and orifice and, if needed, replenished by oil pressure via the supply chamber.

Hope I got that right.

Sherwood

Until you turn the motor off. Depending on the orientation of the cam lobes the cam may want to turn. If the tensioner is weak, or if it leaks out oil, it can collapse. It will then be evident upon startup.

here is how I prime hydraulic tensioners. After assembling. Pump slowly until no more air coming out of bleed nipple and the small bleed hole at the piston. Very easy to do and no doubts if the tensioner is properly primed or not


http://forums.pelicanparts.com/uploa...1505842137.JPG

Sherwood - But it isn't the pump pressure of the oil feed which serves to tension the chain. Someone recently measured what the external relief valve (bleed nipple)pressure is, and it is surprisingly low. Though it shouldn't be high, because the spring pushing that ball down is very small and of low pressure. And the stamped cap with a hole in it which holds the spring is just pressed into its hole, where a ham handed guy like me could accidently dislodge it while misguidedly prying.

Recall that the last iteration before the pressure feds - the Turbo tensioners - had no oil feed at all other than splash and gravity, and worked just fine from all accounts, the main problem apparently having been solved by widening the idler arm bush area.

I've never bothered to pre-oil a pressure fed. After all, what's the point of pressure feeding if it doesn't quickly do the job of filling? During a rebuild, there is still oil in the supply chamber, and when you pull the pin you inserted, the suction is going to draw that oil up into the pressure chamber. I always dry crank an engine after a rebuild until I see oil coming from a loosened cam line fitting anyway.

Trond's device is ingenious, though. I can see how it will produce enough pressure to cause oil to come out of the nipple. But out of the piston top? I have to crank quite a bit with the tensioner in my vice (so I can get the pin in) before that happens, and that's a lot more pressure than the relief valve holds.

Probably a good idea to bleed as shown. Especially with new tensioners. With the exception of doing so with the plunger fully compressed. That way when the plunger is released after being installed there is no possibility of air being drawn into the working chamber. Probably a good idea to check for firmness of the plunger after it is released after install.

I just held my oil can tight against the inlet hole and squirted. It worked will enough to have oil squirt out of the valve at the top.

Well, air ought to be pushed out of the working chamber almost instantly, as its viscosity has to be a whole lot less than that of oil? The old cup and splash tensioners would seem to benefit from prefilling, but with a pressure feed?

Some of this may be akin to the mantra of bleeding brakes starting with the one farthest from the master cylinder. First off, with dual MC chambers front and rear can't make any difference (and with a race two MC setup, this is so in spades). And the travel distance difference side to side can't amount to anything either.

My concern would be IF the supply chamber was empty of oil AND the plunger was allowed to extend, air could be drawn in under the plunger. That may not be cause for concern? IMO, it never hurts to double check everything going into these motors.