Adrian_

As some might know from my other topic, I purchased a project 928 (Euro 79) on which I want to fit a Euro S 4.7 16v engine.

While shopping around for a good one, I took a closer look at the current engine, a 1982 US spec 4.5 engine which is knocking very hard and pushing oil in the throttle housing (at the purchase I simply considered it fubared).

It turns out that, at some poing in it's history, the timing belt jumped: the left cam gear (as looking to the windshield) is badly damaged by the slipping belt. I took today the time and proprerly arranged the timing, and, of course, the engine still knocks .

I was unde rthe impression that 16v engines are non interference and the heads won't get damaged if the belt jumps. Could it be something else, or there are just some bent valves?

I'm thinking to fix this one, in order to be able to enjoy the car. This would allow me to look far more pattiently for the right 4.7 euro spec.

Obviously it wouldn't be interesting to invest in this engine more then it's worth, considering the fact that I'm going to change it anyway and there's not much of a 928 parts market here.
It's clear that I'd need a left cam gear, but is there any way to determine what else, before popping out the heads?

Many thanks in advance for any advice.

Mrmerlin

there is a big difference between a bent valve and a rod knock.
You proabably should figure out what you have.
If its a rod knock it will be making metal.
Get a piece of lamp cord and stick it into the dipstick tube and then drip the oil onto a black piece of cardboard look at the oil in the sun for metallic particles, if you see lots of metal then you should NOT run the engine anymore as it will eventually throw a rod out the side of the block

Adrian_

Thaks for the advice, will do it tomorrow as it's already dark here (10PM).

Question is: could this 16v engine be damaged from the jumped belt, or the knocking has nothing to do with it? If it's a rod knock I won't even bother, if there are just some bent valves it might be a different story. Thing is the knocking is like nothing I've heared before, doesn't sound like rod, doesn't sound like valve.

Imo000

my 83 16V US jumped and it did ever so slightly touch the valves. Mine had some carbon build up and that is what cused the bent valves.

Mrmerlin

if your not sure about the noise have someone that has experience look at it

Adrian_

Experienced 928 mechanics are kinda hard to find in this part of the world. I think I'll buy some automotive stethoscope and try to pinpoint the noise source (if it's just one lol)


Other then bending the valves because of carbon build-up, is there any other damage inherent to a jumped belt on 16v engines?

WallyP

The camshafts have been known to break on the 16-valve engines, and can cause a knocking noise.

86'928S MeteorGrey

Have you done a compression test? I'd go there first.

Adrian_

Wally, that could be it! Would make sense anyway.

Is there any method to check it fast, without removing the heads?

P.S. Didn't bothered with compression test, as I simply considered it fubared. Just today I noticed the damaged left cam gear and started wondering what really happened to the engine.

Mrmerlin

if you can take some pictures and post them it will assist those that want to help figure out whats going on

Adrian_

Will take tomorrow a pic of the damaged left cam gear. Other then that, not really much to see from the outside, engine looks normal.

Can someone describe the procedure (if there's something like that) for removing the cam? Or is there other secret 928 way to see if it's intact? (could drag the car to a compression test, but it's rather uncomfortable- the traffic is very crowded here during working hours and with the engine not running you have no power steering aso)

Adrian_

Here goes the picture. You can clearly see the damaged teeth of the cam gear

Other that that there's nothing wrong on the exterior of the engine.




Can someone tell me if there's a way to take out the cam without removing the tower? (please elaborate )

Imo000

Wow… that’s worn down to a stub. Most of the cams break at the end, right near the cam gear so if you can take the gear off, you can examine the cam shaft.

Adrian_

I'll remove the gear tomorrow (already 1.24 AM here) and check it out.

If the cam broke what else should I expect to be damaged?

karl ruiter

Top end is quite inexpensive and pretty easy to do, even if valves are bent. Normally they would not be on that motor, but there are a couple of possibilities like carbon build up or possible Euro S heads installed rather than the stock 4.5l heads. I recently bent some valves on my 4.5l motor with Euro S heads following a belt slip. No knocking noise, though. Just would not run.