Cam Shaft Timing

[Porsche_monkey]

Suppose you had a way to pressurize the chain tensioner (50 psi oil?) during assembly. Wouldn't that be better than using the vice-grip / tension tool, then installing the tensioners?

I know the LHS might interfere with the cam nut torquing, but it would help on the RHS wouldn't it?

[dtw]

I am sure to get jumped on for this - but I can offer my small experience.

The first time I did timing was on a motor with narrow angle, high-lift cams. I was targeting lift @TDC to be 4.4mm. Though I had solid tensioners that I used for actual final timing, I tried out some oil-fed tensioners just for fun to see how much difference they made. My experience was that the hot cams came on so steeply, that the torque I was applying to the crank during timing caused the tensioner to begin compressing before the cam would finally come around. Thus: BAD timing reading.

Then I timed a 3.2 motor with stock DME cams. I believe the lift at TDC was around 1.25mm. This time only the oil-fed tensioners were fitted for timing. Due to the easier approach angle on cam lift and the lower overall lift required, the tensioner didn't even begin to deflect during timing.

I guess the answer is - it depends on the cam? In my experience just using the oil-fed units will work fine for any lazy CIS/DME cam.

[Superman]

I believe that oil pressure acts as a shock, not as a spring. The pressure-fed tensioners use spring tension and oil pressure damping. So, adding pressure does nothing for this operation.

[Porsche_monkey]

Originally posted by Superman
I believe that oil pressure acts as a shock, not as a spring. The pressure-fed tensioners use spring tension and oil pressure damping. So, adding pressure does nothing for this operation.

I did not know that. Anyone else care to confirm this? I assume you are saying the oil is basically a back-up, like a hydraulic lifter?

[Doug Zielke]

Originally posted by Superman
I believe that oil pressure acts as a shock, not as a spring. The pressure-fed tensioners use spring tension and oil pressure damping. So, adding pressure does nothing for this operation.

My understanding also.
Much like oil-filled shock absorbers used for suspension.

[Porsche_monkey]

So..... why don't I set the timing with the spring/oil fed tensioner?

[ischmitz]

I don't think the oil acts as dampener only. At least on my 964 oil-fed tensioners I thought one was frozen when I played with it. I could not move the plunger at all first. Then I found there is a check valve. When I relieved the pressure on the check valve a lot of oil pured out and the plunger moved much easier only restricted by the spring.

Ingo

[Porsche_monkey]

I think the check valve is what allows the oil to act as a back-up / shock absorber behind the spring.

[NevenM]

Hi

I think you are all right and wrong, In reality the tensioner is probably misnamed as it is not necesary to 'tension' the chain on the relaxed side
in most circumstances, (maybe on a vicious decellaration). The spring and oil act as a ratchet, as the chain thrashes around the spring extends the tensioner and the oil keeps it there, This system needs some give (which is why mechanical tensioners kill chains), The pressure fed tensioners have the advantage of being an open system, ie oil that is lost is replaced.

Neven

[NevenM]

Hi

Further to my post above the reason you don't use tensioners during cam timing (The factory manual actually suggests jamming a piece of metal between tensioner body and the arm) is that you are trying to emulate the engines running condition, so you are using the tensioner to
try and get the driven side of the chain into as close a state of when it is
running as possible ie in more tension than is required to turn the cam on the bench. Also if you had both inlet and exhaust rockers installed the
exhaust rocker at overlap TDC would be pushing the cam forward.

Neven

[ChrisBennet]

It's important to get the cam timing the same on both cams, probably more important than what they are actually timed to.

Whatever method you use to time the cams, you need to get repeatable measurements. Check your dial indicator reading at TDC, turn the motor over two rotations, check again, repeat a few more times. If you don't get the same measurement every time you come up to TDC for that bank, try something different (tighten clamp, use different method, check for too much lube on cam, etc) until you get consistent measurements.

The factory tool (P204) works great for tensioning the cams.



I don't see it listed in Pelican's catalog but they can probably get it. SIR Tools makes it.
-Chris

[911pcars]

Here's what I gather from various part descriptions: The oil-fed tensioner acts like a hydraulic lifter to maintain the proper tension regardless of chain wear and dimension changes due to temperature. Oil is fed to it constantly via the engine oil pump. Oil bleeds out of the tensioner via the clearance between the tensioner body and the piston. The check valve prevents oil drainage when the engine is OFF.

Since the rod extension of the hydraulic tensioner varies, while timing the cams you should substitute a fixed-length mechanical device as Chris shows or a mechanical tensioner (as others have suggested). You can fabricate a mechanical tensioner for this purpose using an old tensioner body.

Sherwood

[jgparker]

Pelican does have it:

PEL-TOL-P204

http://www.pelicanparts.com/cgi-bin/dbsql/db.cgi?db=partsearch&mh=20&view_records=yes&uid=default&description=PEL-TOL-P204&I1.x=14&I1.y=10

I wouldn't do without this tool myself. You can actually use it without removing the tensionser is some cases.

JP

[ChrisBennet]

When I searched before I found that part # but when I clicked to get the photo I got a picture of a tensioner holder instead. Did they fix the link today?
-Chris

[Wayne 962]

There's a bunch of mis-information in this thread. Here are some corrections:

- The hydraulic tensioners indeed have a spring inside of them. However, this spring is not very strong (compared to the old-style tensioners) and is not adequate for timing the cams under any circumstances.

- You definitely need to make sure that the chain is tensioned on the "relaxed side" or the chain may skip a tooth. This is what happens when tensioners fail

- The hydraulic tensioner are oil-fed with a hydraulic check valve. Even when there is no oil pressure, the check valve prevents oil from exiting the tensioner quickly, and the tensioner can then feel stiff. If you check the Engine Rebuild Book, I explain the operation of these, and what to expect from them when compressing them in a vice.

The P204 tool is the correct one, as shown in the link above...

-Wayne