The V8 Owners Forum -

As some of you may remember I have a problem with a knocking noise on one cylinder on the the seconhand 3.5 RV8 I have been isntalling in my TR7 the current situation is:

- It is fine when cold
- It starts knocking after approx 30 minutes of idling with the electric fan cutting in and out (I havent driven it any distance yet)
- It is only one cylinder(2nd on left) when I remove the plug lead the noise virtualy disappears and the engine rpm drops by the same amount as removing a lead on all of the others.
- Oil pressure at this point is 15-20psi (approx 600rpm)
- I tried running it with the rocker cover removed, there was still a valve clearance
- I have removed the sump and checked the big ends which look very good and have no uneven wear / play etc, the bores also look goood with the honing marks still clearly visible.

I have therefore come to the conclusion that it must be the piston, little end or con rod.

have I missed anything?

I plan to remove the piston next week, I understand the gudgen pin is a press fit in the con rod, I have a 30ton press which i assume will be more than enough to remove the pin, but I have a couple of questions:

does anyone know what the spec for the bore in the con rod is?
When I press it back together do I assume I set it up such that the con rod is central on the gudgen pin or am I misssing something


Kevin

Kevin,

Before you start tearing the engine apart, what ex. manifolds do you have if tubular thay are notorious for warpage and the knock you are describing can be caused by an exhaust manifold not sealing properley, it can also happen with cast manifolds and it's worth getting some heavy duty ex, gaskets from real steel.

If the engine is in as good condition as you describe I would be surprised if its a small end.

I just inspected some rods and pistons off a 3.9 engine and with over 100.000 miles there was no noticeable wear in the small ends.

Hope it's simple,

Kevin Jackson.

Kevin,

Forgot to answer your question, as far as I know the gudgeon pin size for the 3.5 is 0.874" so for a press fit the small end will have to be slightly smaller.

The con rod small end is offset on a V8 so make sure it goes back the same way round, and the rod end should be centred in the piston when it's back in the bore.

I've a feeling that it is the gasket because when you remove the plug lead the noise diminishes but is still there which could be that you have no combustion but are still pumping unexpanded gases so the noise would be reduced.

Kevin.

Kevin.

Kevin

I agree with Kevin.

My RV8 sounded dreadfull.

Recently I removed the exhaust manifolds to find them all twisted, and blowing on at least 5 cylinders, and up to 1mm out. They are nearly new Stainless Tubular Ceramic coated block huggers so I was not too happy.

To cut a long story short I could find nobody who would machine them so I bought a hand sander and filed them down myself. It took ages.

I have fitted them with composite gaskets and RTV sealant.

They should sound much better. (when I get around to finishing the build.)

Dave

Well,
I find it difficult to believe such a metalic knock coud be from the exhaust but It looks like you guys may be on to something, I found the bolts on the exhaust manifold were only finger tight for the same port, I have re-fitted the gasket wiith some cement and after a hour or so driving only heard the knock once or twice and then only a single knock and not continous, looking at it it is still leaking and it appears the manifold is warped slightly(it is a standard SD1 part), also it is compounded by the fact that the bolts I bought appear as it they were intended for a tubular manifold with thinner flanges and only have approx 10mm of thread engagement in the head.
Either that or it was piston slap or something which has improved as things have bedded down with mileage.

So now I will buy some longer bolts try to sort out the manifold and use it for a while to see what happens.

Next thing is to sort out the LPG , improve the exhaust etc etc. I don't think it will ever be completely finished.

Many thanks kevin

Hi
If you have been running LPG with a blowing exhaust gasket area it is a pretty good chance of some damage to the gaketing faces and will have burnt the face where it was blowing. Would be worth taking the whole lot off, re facing the head and the manifold (with an oil stone, by hand) until there is no depression/burnt area in the faces where it was blowing and putting it all back together with a new gasket. (and longer studs )
Mike

Kevin,
Your welcome, If you only getting the knock ocasionally now i would suggest the exhaust system itself could be putting some stress on the manifold, did the noise come back when you were going round a corner?

Did you get the heavy duty gaskets from Real Steel 01895 440505 they are lot thicker than the standard ones at 2.5mm and have much better sealing properties.

Kevin.

Kevin,
At the moment all I have done is refitted the standard gaskets with some paste and tighted up the bolts, just to see if it has any effect.
As it seems ot have I will now take the manifold off and try to flatten the face off as best as possible then re-fit with the real steel gaskets.
You may well be right about the exhaust as well as the knocks seem to be during gear changes etc when you back out the throttle not on accel.


As for damage due to LPG, it has not really run properly on LPG yet so this should not be a problem.