Thom

With either of the 3 cam towers (and 4 camshafts and 3 cam pulleys) that have been used, the timing belt has always aligned with the cam pulley and the crank pulley. There is no indication that it could have been progressively moving towards either of the outer edges of the cam pulley, as it has always sat aligned with the middle plane of the cam pulley.
I could be wrong, but this suggests to me that there is no odd angle between mating surfaces - cam housing/head and head/block.

Valve stem heights are all within spec, valves have not been cut up and valve springs "preload" has been set as described in the FSM, both when the head was initially assembled and when I replaced retainers.

Though Ti retainers and standard retainers are not 100% identically-shaped, they have the exact same geometrical impact on valve spring "preload".
They only differ in the distance between their upper ridge and the top of valve stems.

I use the term "preload" with brackets, as whenever I have talked about "preload" in this thread, I was referencing the preload described in the FSM, which is a distance, and therefore assumes that valve springs are all of the exact same stiffness, which is where I now have my doubts - if valve springs are not all of the same stiffness, then I can adjust the "preload" distance as much as I want but the physical preload will still remain too high for the springs that are possibly stiffer than they should, so the next step before resigning to take the head off is to check if all valve springs, which were new when I first assembled the head, actually are all of the same stiffness.

If I can't put in evidence possibly different valve spring sitffnesses as I have them out then I will probably swap valve springs between a noisy lifter and a quiet one.
It's not as if taking off the cam housing and putting it back once more with getting no result should bother me any more, anyway :^)

Thom

After leaving the car in a corner for a while and doing a bit of a cold rethink it is simply possible that the latest cam + lifters I have been using with the standard retainers were damaged when I was running them with the Ti retainers, even though they ran together for only about 80 miles - at the time I installed the standard retainers, all the lifters and cams I had at disposal had run at least 80 miles with the Ti retainers, so I had no "innocent" cam or lifter to try out.

I listened to a friend's engine and even though it's running fully quiet when standing in front of it, the lifters' noise pattern when listening with a screwdriver on the cam housing is exacly the same as on my engine. This suggests to me that I may not be having any actual issue with oil pressure...

Thom

Quick update.

I did several thousand km with the latest cam housing + lifters + camshaft. I was till having a light ticking noise, located on valve #4.

So I took off the cam housing to notice that all lifters and cam lobes look fine, except lifter #4 and cam lobe #4. See pic below of cam lobe #4.
It shows the lobe was beginning to flatten, like was the case with all previous camshafts used. It definitely is not as bad as it was when the faulty Ti retainers were used, though.

I rechecked all valve springs installed heights, all are within spec. I now have all valves springs removed. I don't have a tool to measure actual valve spring stiffness in lbs but I have not been able to put in evidence a possible difference in stiffness between springs pair #4 and all the others.

Valve stem heights are correct, preload heights are correct, everything is set as it should be.

Can anyone with spare valve springs please tell me how many lbs they develop at a compressed height of 41mm?

bebbetufs

How do the other lobes look? No triangular wear?

TurboTommy

Next time you run the engine, open up all those large allen key nuts (don't really know what they're called) on the cam tower and look in there with a good light.
(At idle there's very little oil splash, so it's not messy at all; you'll be able to see while it's running).
You might learn if all eight lifters are getting wet with oil with the same consistency. Do this with a cold engine so you know the lifters aren't wet from recent higher RPM run.
Just in case we are still pointing to a potential oiling problem.

Tom M'Guinn

Although my original performance cam was welded, I'm sure it was properly hardened and it had a similar wear on top of the lobe. Is the 2.7 cam tower the same part number of the 2.5? I wonder if there is some odd geometry issue with the 2.7 head with 951 tower/cam?

PET shows the same tower numbers as best I can tell, and I know this combo has been used by plenty (including myself now), but seems like an odd coincidence that Thom's motor and mine both flattened a cam lobe. It may indeed by nothing more than a coincidence, but makes you wonder.

reno808

hmmmm

Thom

I checked the rates of the valve springs and they all returned +- 130 psi at a preload of 41mm.
Then I tripled checked again the compressed lengths of the springs as installed and the distances actually appear to be all correct - 41mm intake, 40mm exhaust.

The 4th, damaged lifter was a then new INA lifter while all the others were good used lifters. See the first picture below. As can be seen, lifter #4 doesn't look good and is bad. I can feel with my finger that it is not flat anymore and feel like sand paper.
While all the others don't look exactly identical between each other, they all feel flat & smooth.

Last week I had put on a another good used camshaft with another set of good used lifters. Lifters were empty as I started the engine, but after they had filled up the noise on 4th was still present. I went off for a 20 mile drive, came home to notice the noise on #4 was still present, I then took off the cam housing and noticed that lifters #1, #5 and #7 were showing marks that suggest they were beginning to turn bad. Picture 2 shows this other set of lifters. All were good used at the time of install. Camshaft was good before this last run and is still good after.
Could the 3 lifters that look bad, but have not turned bad yet, have suffered more than the others during the initial fill up? I'm completely puzzled that #4 now shows no sign of damage while it is the only one ticking?

Tom M'Guinn

How about your valve guides -- who installed them and and chance they are too tight?

Thom

I think guides are ok. The shop that did the head has a zero failure rate as far as heads are concerned and has good experience with 951 heads.
When I slide valves into the guides they all feel the same without any play.

Assuming now back again that the issue is oil-pressure related.
This is a 968 block, with oil squirters. They should open when pressure is 3.8 bar in the block. I added last year a Kiss oil cooler. Theoretically, increasing the volume of the oil loop means reducing peak oil pressure. Could that be possible, even if the pressure gauge in the dash has never returned any funning reading?

lee101315

I wonder if theres an easy way you could shim the oil pressure relief valve so it opens 10-15 psi higher.

Thom

Good point Lee, I may have a look at this if checking the valvetrain leads nowhere.

Today I put it all back together, this time with the same camshaft/lifter combo as during the last run, only difference is that I removed all preload shims.
I had 2mm of shims under each valve, and while the noise is still present I think it is a bit quieter than it was with the shims. The engine feels a bit smoother too and still goes like stink, even more so with the 9R cam - consolation prize

Should that distance of 3mm be absolutely constant when using stock valves and stock retainers?

I am seeing 3mm on intake valves and 4mm on exhaust valves. Should that suggest my intake valves may have been cut?

blade7

I would expect any decent machine shop to cut the valves/seats to ensure the valves were the same height in the combustion chamber, also to pay particular attention to guide clearance, I know my head guy had to ream the new guides on my Ford Cosworth turbo head years ago. You've changed towers, cams and followers if the problem persists maybe it's time to pull the head.

Tom M'Guinn

I don't know, but will confirm tomorrow that mine (in the old 951 motor on a stand) are consistent across the board. Can't off hand think why they would/should differ. Was your bad lobe an exhaust or intake?

evil 944t

If your aftermarket cam's base circles are smaller or you have high lift, it is possible your lifters are not pumping up because the oil feed is not "inline" with the lifter hole.