The Verdict!!

[terryinfrance]

To put all my readers out of thier misery,we have a verdict re.cause of all my probs.
Surprise,surprise.Its PISTON SLAP.
after having a close inspection of the head and poss cause,noisy vac pump suspected,and tight inlet valves.
Well it was neither.I decided to have a more detailed look at the bores and pistons.
I was initially thrown off track because of the seemingly lack of bore wear,original honing visible and lack of ridging at bore top.
However this afternoon I decided to try and give the pistons a good wobble.
No.1 piston moved quite a bit and gave a definite clang as it deflected off the bore.
This was the noise!!
It has been suggested by a pal that a new set of pistons should do the trick as the wear is in the piston and not the bore.
Would readers recommend this as a viable remedy.
It should not be too much of a hardship to remove them with the head off and sump access good.
Opinions please.
Terry

[NiSk]

Since you've already got the head off, you can easily check the cylinder bores for out-of-round with a suitable dial gauge mounted on a triagular frame (all engine shops use these). That way you'll know if you're in the clear. A good engine shop should help you determine what the best solution is (new pistons and a re-hone, or . . . )
//NiSk

[CITMAN]

Dave Burns Comment:
<b>If you take the head off don't be too alarmed at lateral piston movement when cold, they will move.
Check for a lip at the tops of the bores, if you drag a finger nail up them and it snags on a pronounced lip then thats not good, there should be hardly any, don't mistake it for carbon buildup though.</b>

[jeremy]

You have anumber of options some of which will depend on how much your are prepared to spend on the car.
So far as good piston sealing is concerned ovality of the bores is the biggest problem. Ideally you will measure this using the appropriate micrometer device but I doubt if you have access to one. Snap on do some but I think they are about £125 + VAT etc. Haynes suggests rough measurements can be made by inserting feeler gauges between a piston (without rings) and the bore walls. The bottom of the bore (below the ring travel) will be unworn and this shouldbe compared with the top just below the ring. Haynes suggests the max out of round or taper should be less than 0.1mm
I don't see why you need new pistons unless yours are worn. When you remove them you should replace them if they are burnt or damaged or the ring grooves are worn. Otherwise a new set of rings should work but be sure to get proper replacement ones with 'ridge dodger' top rings as standard manufacturers new ones will hit the ridge at the top of the bores.
Have fun
Jeremy

[Jonesy]

I think you have to ask yourself whether its worth putting a new set of pistons/rings in.
I would definitely check the 'ovality' of the bores first, to establish whats going on.
Presumably you would put new 'big end' shells in? If this is so, then ideally you would put a new set of mains in as well (obviously much bigger job).

[Dave Burns]

I once bought a new set of pistons for a 21/4 petrol land rover, they didn't look any better a fit than the ones that were to come out, you could look down the side of them in the bore and clearly see the rings, I took them back and scrapped the engine.
If you get a set I hope you aren't disapointed with what you end up looking at as I was, if you are satisfied that they are going to be better, don't forget that you must glaze bust the bores for the new rings to bed in ok.
Dave

[alan s]

Does anyone "shot pein" pistons over your way? It's a process that used to be call Koetherizing where they basically stretch the piston by blasting shot (steel) pellets on the inside of the piston in a controlled situation to take up the slack. Used to be much cheaper than new pistons or rebores & O/S pistons.
Someone will need to do an accurate measure of the bore though; be a bugger to get them back & find they're too big hey...[}:)][:D]
Alan S