348 Checking Cam Timing & my engine brief knock

This could only work if the number of teeth of the belt is an exact multiple of the number of teeth on the cam sprocket. Otherwise, the belt will "travel" over the cam sprocket and any marks on the belt and the sprocket will go out of synch (and come beck in synch only once in a number of the belt full rotations).

However, I just found out (in the service manual) that there is a provision for easy check of the cam timing. It is approximate but good enough to spot a skip by one tooth (or more). It can be done by positioning the engine in Cyl. 1 TDC (in combustion stroke) and looking through the slots in the belt top covers:

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As I wrote in the"MAF Adjustment" thread, when I started my engine (cold) on the day, it immediately produced a fairly rapid sharp metallic knocking sound which, after a switch off and restart, practically disappeared. The previous day, the engine started and idled (as always) nice and smooth and I did not drive the car but just had the engine idle ~ 10 min. while taking the EGT readings.

I looked at the piston crowns with a borescope but could not see any "shiny moons". However, the borescope I have produces a rather grainy picture and its light (the LED-s) is not really bright so I ordered another one with much higher resolution.

In a few days, I will check the cam sprockets positions as per the pic above and inform on the findings.

 

Milo, I see an engine out in your future ....

 

not so sure check this timing marks to begin with but it could have just been an exhaust rattle or something along those lines..

Those are the timing marks that I was talking about making white paint marker marks on the belt and pulley on all 4 so it's much easier to see visually

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Me too, in the near future even if I find that something else (benign) caused the knocking. Other than the belt skip, I think of the possibility that the big nut on the back of the "pumpkin" may have come a bit loose. The reason why this may be a possibility is the fact that, when I regreased the flywheel some 3-4 years ago, I did not tighten the nut to the required torque but just tightened it with quite a powerful impact gun then torqued the centre allen grub screw to correct torque. Will check this out when I have time to remove the rear bumper and the exhaust.

 

Did some further checks today. With the spark plugs removed, cranked the engine - absolutely no knocking or even slightest ticking sound, smooth. Went to reading the compression (first time) but could not do it properly as I found that my compression testing kit did not have M12 adapter for the extension hose. Instead, I used the press-on extension pipe which was hard to keep in place due to high push-back on compression stroke. Anyhow, my readings are as follows (cold engine, throttle butterflies closed).

1 - 240
2 - 240
3 - no reading, space constraint
4 - no reading, space constraint
5 - 200
6 - 200
7 - 200
8 - 200

I will repeat the test once I find (or make) an M12 screw-in adapter.

Could not check the cam timing as I put an M14 thread (part of an old spark plug) on my DIY extra long dial gauge (pic below) without checking the thread of the 348 spark plugs. Will have to make another "Ferrari" adapter for it.

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Assuming that your Cyl 3 and Cyl 4 are also 240 psi, I am not sure I like that result.

 

I was also surprised with so high readings. I can only think of, perhaps, overskimmed head in the past.

 

Or a mis-timed cam shaft.
Or a lot of carbon build up in the chambers but that is unlikely to be in all four cylinders.

 

That assumes anyone would bother to ensure those secondary marks are in place when cam timing. I for example never do because there is absolutely no value there. I absolutely do not care what the cogs show. I always pull cogs to cam time. I only care what the cam timing is.

 

I don't think mis-timed camshaft(s) could cause higher compression readings but could possibly cause lower readings (talking about "static" compression at low cranking rpm-s). In any case, I think that, for the cam timing to start affecting the compression readings (in whichever way), it would have to be so much out that it would cause contact valve-piston.

Carbon build-up is a possibility as I have not driven the car much over the last couple of years, mostly starting the engine regularly and keeping it at idling only. Looking inside with my poor resolution borescope and not strong enough lighting by its LEDs, I only see black piston tops and cannot distinguish the "rectangle" and the circle inside it. When I receive a better borescope I bought, will have another look.

After spinning the engine (spark plugs out) which showed no "bad" sounds at all and after getting the initial compression readings I showed earlier, I now believe that the "sharp metallic knocking sound" I suddenly had upon the first start of cold engine (switched off after a few seconds, went away on second start) was probably fairly strong detonation in the cylinders which can sound very "metallic". This is for two reasons: 1. it appears that I have quite a bit of carbon build-up and 2. the petrol in the tank (just realised) is more than 1 year old.

I will drain the old and put in fresh fuel (I use Shell V-Power Racing, highest octane available here) and, if the engine runs well again, go for a number of "Italian tunings". I may also look for a good carbon burn-off additive - any recommendations?

 

I totally agree, the marks on the sprockets against the slots on the covers are a very rough indication. I will use them just to see where roughly my cam timing is but it appears that I had no contact valve-piston and that the "knocking" was actually brief detonation in the cylinders (my post above).

 

I did another compression check today (cold engine, throttle closed) using a proper screw-in hose and got more reasonable readings:

1 183
2 182
3 183
4 183
5 150
6 150
7 150
8 150

Still, a large difference between right (higher) and left (lower) banks. I looked at the backs of my heads where they contact the gasket and, on the left (lower compression) head, I can see a small step in the head casting just above the line of the top of the gasket (the step shown on the sample pic below, rotated) but I see no such step on my right (higher compression) head. Where the line of the step should be seen, I have the head gasket. I suspect my right head has been skimmed by the PO which would explain the compression difference.

I would appreciate if someone can confirm that both (unskimmed) heads should have the mentioned step. If somebody has a right head lying around, please post a picture at a similar angle as this picture (I could not find a similar angle picture for the right head).

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I received a good resolution borescobe and inspected the pistons again - absolutely no signs of valve impact. Also checked the cam timing and, since I was using the approximate marks on the belt covers and the marks on the sprockets, I will say that the timing of all four cams is "approximately spot-on". I have still not re-started the engine but will do shortly.

My final conclusion is that the metallic knocking I had was actually produced by detonation (self ignition) in the left bank. This sound actually came after I, as part of my attempt to equalise the left and right EGTs, changed the left MAF's CO screw from the existing 383 ohm to 400 ohm to make the open loop mixture leaner. The engine started fine but, after a few seconds, the knocking came. I put the CO screw back at 383 ohm, re-started the engine and the knocking was still there for the first few seconds then disappeared but, as I heard a couple of random faint knocks after that, I finally switched the engine off. It would have probably cleared had I left it idle a bit longer but I was preoccupied (frightened) with thinking of a skipped timing belt and piston-valve contact. It appears that a relatively small change of the CO pot resistance from 383 to 400 ohm causes the mixture to get significantly leaner resulting in detonation.

With regard to my compression difference left-right, I am now almost sure that my right head has been over-skimmed in the past causing 20% higher compression. I took pictures (using the new borescope) of the backs of both heads showing that the left (lower compression) head has a small step just above the gasket and, on the right (higher compression) head, it appears that the step has been shaved-off. So, I will be looking for a good right bare cylinder head to replace the existing one during the next engine out service.

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If you are worried about the head, I would take both off and CC the combustion chambers before replacing anything. A rough calculation based on your 150 and 183 numbers would suggest a 17% reduction in combustion chamber volume due to shaving the head. Seems a lot.

 

Yup that head got worked on and it appears they shaved off just past the limit.

 

That sure seems like alot to remove. Usually it's not particularly visible to the eye when they shave a head in general. That's very noticeable.

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When I bought the car (had 9+ k miles only, now 14 k miles), the only record I found was at "Naza Italia", the Malaysian Ferrari authrised agent. The record showed timing belt and a few other things that I did not pay much attention to at the time (no head work mentioned). I found out that they did this service by their sticker (aluminium plate) in the engine compartment showing belt changed at 9,xxx miles, next change: 59,000 miles and no date limit. 50k miles interval (?), no date limit - I immediately wondered how they got the Ferrari authorisation.

Now I suspect that the belt change was done not as part of regular maintenance but as part of engine breakdown repair due to (common here) overheating. And cylinder heads are skimmed with no regard to the limit, as long as the engine still runs "ok, whaat" after that.

Has anybody heard of special thick 348 head gaskets? - alternative to buying another head

 

from pics it looks like Too much

 

there is a guy here that custom makes gaskets from Australia iirc. I forget the name. Rifle driver knows him.

 

Thanks. Any experience with this company (Custer, Washington) - https://www.nicksforzaferrari.net/nff-custom-ferrari-head-gaskets.html

 

Yes, agreed. Just seems like a lot would have to be taken off the head to get that difference in compression. Rough estimate is more than 1. mm. That step doesn't look that high. But if the engine has to come out I'd certainly check the cam timing before I'd pull the head off. I mean, to me it's not that 180 looks high, rather 150 looks low, even for a cold engine with throttle closed. But if the intake skipped a tooth and is closing late on that bank..... Of course, I don't know how many cranks Miro did on the CT which would also effect pressure.

 

What I was saying is that more than that step would have had been milled off. Seems like a lot.

 

I cranked the engine during the CT, on every cylinder, until the gauge stopped climbing any further. I don't suspect a skipped tooth as the sprocket marks are well aligned with the slots on the covers (a quick check recommended by the manual) and, however approximate this indication is, a skipped tooth would have certainly been detectable.

On the other hand, I seem to have a well over-skimmed right head so I take that as the main suspect. Judging by the shots I took, it looks to me that the right head is at least 0.5 mm lower and probably more. A couple of years ago, I had to replace both heads on my Daimler Super V8 (4 Lit. supercharged), maintained/repaired by the PO using local "specialist". I found that both heads had been skimmed by about 0.8 mm (74 k miles engine).

I will try to find a thick custom made gasket, perhaps at the link I provided above or elsewhere, but I am much more inclined to just buy another good right head, preferably bare (cheaper), when I find one that I can verify it has not been skimmed or skimmed very little (wish me luck).

 

No argument with the pictures. But like I said, if you pull the heads cc them before replacing to be sure.

Still, if you cranked, cold, throttles closed, until the gauge stopped moving, 150 psi seems awfully low for an engine with 10.4:1 compression. If 150 was normal, to get to 180+ would mean that the compression ratio was raised to around 12.5:1 by the skimming. If the compression was raised that much I would also expect a lot knocking when running since the timing would still be set for an engine with 10.4:1.

Just throwing this out there for thought.

 

Taking compression readings on a cold engine is not a proper way and will produce somewhat lower pressures so I am not too concerned about 150 psi left but I am concerned about 180 psi right. On one cylinder, I took readings with closed and then with fully open throttle - the reading with fully open was ~5 psi lower. I expected a bit higher but that's how it was. The compression at low (cranking) rpms is very different from the dynamic compression at higher rpms. I believe that the reason why I had somewhat lower compression at WOT is the fact that, at cranking rpms, the piston in the compression stroke staring from BDC first pushes some sucked-in air back out through the still open inlet valve before it starts compressing it. It is possible that less air is pushed back out through the intake with the closed throttle (restriction) then at WOT resulting in slightly higher pressure reading with the throttle closed.

I have yet to take the compression reading with a warm engine. When I took the very first readings with the press-on tube adapter for the gauge, the engine was slightly warm from about 10 seconds of running (and detonating) and those readings were 200 psi left and 240 psi right so there we go. I calibrated the gauge after that and it showed accurate.