Small Knocking Sound

I have just finished working on my engine I had to replace a cam follower because I broke it (as mentioned in a previous post).  I also need to redo the timing due to another mis-hap resulting in the crankshaft bolt coming out.  :?

I replaced the timing belt everything back together and she started. The engine seemed to be running fine.

I then proceeded to replace all the filters and the oil. I then ran the engine up for a bit while it was running I could hear a small knocking sound. It sounds like its coming from the top of the engine.

The knocking sound is not consent it comes and goes. I have not had chance to re-shim the new follower I am using the old shim could this cause this noise I would have thought it would have been move of a tap than a knock.

The car is 1.8 GTI CAB with a DX engine

I would seem that this only occurs once the engines warmed up.
 Any idears?

didn't leave a spanner in the rocker, did you?

Can you set the valve clearances on a watercooled like you can on an aircooled, maybe that would be first to check.

I had a similar problem on my camper, it was a small knocking from the top of the engine, it turned out to be a valve guide. Basically a small copper tube had worn, meaning that everytime the valve closed it didnt seat correctly causing the knocking sound.

Hope this helps. Mark.

dx have hydraulic followers so dont need re shimming(?)
when the noise is present is it rev specific?
any loss in power / misfire / backfire?
i think marks right about the valve guide, either that or a slightly bent valve perhaps.

I've checked the engine and its a DX. But it deffinatly has shims.

The car has made a couple of backfire's since this happened never did befor i touched it.

Is there anything you can to see if the valves maybe bent without taking the top of the engine off?

Didn't think DX's were hydraulic…mine certainly isn't - when they went hydraulic for later cabbies did they put hydraulic tappets on the DX engine, or did the code change? Somebody out there is bound to know this!
I've got a similar problem after part rebuilding my DX engine for piston ring change - tapping from one cylinder top end. I did a fairly basic job, and didn't strip everything - just head off, sump off, pistons out, new rings and all back together.
I thought tapping was due to a broken ring, but it looks likely that it's a valve touching the piston!!! Compression is now excellent, but valve clearances are all  too tight -especially exhaust valves. Peeping in the spark plug hole I can see a shiny patch on the edges of the 'cutout' in one piston…so this weekend it's a reshim job and hope it cures the problem without damage!
I know I should have checked the tappets, but…you know how it is…
Worth considering for yours!

DX are mechanical tappets (not hydraulic) and yes if it goes away when warm it is likely to be the valve clearances. Get some feeler guages and measure them up - check haynes for the ranges allowed. Take the shims you have in out, measure them with a micrometer (if the thickness is not stamped on them) and work out what thickness ones you need to buy to get the clearances within tolerance.

Best measured when the engine is warm…

later dx's ARE hydraulic!

http://www.clubgti.com/forum/showthread.php?t=107003&highlight=hydraulic+dx

and as yours is an 86 and the changeover was in 85 you do have a hydraulic head ok!!

Ahhh. Didn't realise that. Stand corrected!

Yes, I've just tried to borrow some shims from the two spare DX engines which I have…only to find they're both hydraulic heads!!! If I'd realised this, I might have swapped the heads over when I was doing the piston rings (haven't run either engine, though, so don't know what troubles they may have!). I used to have a bag of shims, but it seems to have vanished…oh well…
Anyway, confirmation that later DXs have hydraulic tappets…

Do hydraulic still have shims? Since my DX deffinatly has shims. I've also replaced one of the cam followers on it and didn't seem to be hydraulic.
The knocking noise occurs once the engine has warmed up when it cold there is no noise but it seems not to run so well.
The engine makes quite a severe rattel/knocking noise at about 2000rpm then it seems to be less but still very present above that.

no if its hydraulic it does away with the shims,  but the heads are interchangable.

simon

You can recognise hydraulic tappets in that a) they don't have a shim sitting on the top, and b) they have a little circular oil groove half way down the side.

Getting back to the point, its probably one of the hydraulic tappets is sticky. Before resigning yourself to removing the camshaft and replacing them, you could try a decent engine flush (a litre of ATF for a little while, is ideal.....), this should clean up the insides of the engine nicely and will probably revive a sticky bucket tappet.

50% parafin,50% cheap 20w50 oil is a good flush,ive done loads of sierras and escorts with the cvh engines,always works,ive even cured a 20valve audi a4 with my magic potion  :wink:  
Bert

I deffintaly do not have hydraulic tappets.
I've had the camshaft out already since i had to replace a damaged tappet bucket.
At the same time I also did the timing belt twice. The first time i did it, it ran  but not well at all. Then the second attempt was much much better. But now i have the knocking.

The timing was out on the engine for a littel bit is it possible that there could be damage to the valves? if so how can you check?

Its likely that ive made some error in doing this. Which is causing the engine not to run so smooth and produce this knocking when warm. I think the engine could do with a flush would this mean replacing the oil since ive only just put in a fresh batch?

If you had damaged the valves it would knock when cold too I would have thought. No harm in giving the engine a good flush. Try berts method or the 1/2 litre atf. Either should clean up the insides nicely.

Are you sure the knocking is coming from the engine???

I'll give the engine flush a go this evening hopefully.
Yeah im sure its coming from the engine i think the its from the top half but its so hard to tell.
Thanks for the advise guys.

sounds like your in need of a stethoscope or use a long screwdriver to help identify where this noise is comin from.