Club 80-90 Forums

Hello all. I have a slight problem!

A long story short i had a bigish overheat, removed the cylinder to find this-



If you look closley at the foto you can see in the top of the piston head indentations from where its been hitting the valves. This is the case with every piston. Theres probably no end of damage to the existing valves-the head is cracked in 4 places and the No.1 injector seat has a gaping hole in it causing it to smoke so i'm gonna put a new complete cylinder head with new camshaft and valves, when i get the head it will already be built by AMC and ready to go.

There must have been an issue with the timing during the previous owners time with the van to cause this to happen, is it common?

I've decided that while the head is off i may as well service the engine, i'm gonna remove the block and completly rebuild it, could anyone give any pointers as to what i should DEFINATLY replace and things that could possibly need replacing?

I think i'm looking at new pistonheaads, what kind of BP figure am i looking at?

Also if the cylinders need reboring do i need to get slightly bigger piston heads, or use the same size as i have now but with bigger rings?


Cracked between the valves on every cylinder!

Last question! I'm buying a new already assembled head from AMC will it be set up and ready to go straight on to the block?

Many thanks,

Rob.

Those cracks are normal - they cause no problems and most people have them. Are you sure that the correct head gasket was used previously ( if it was too thin you would get the valves hitting the pistons - there is a choice of three) It looks as though a too thin one was used possibly after a head skim.

Below copied from Brickwerks:

Please measure piston projection from the cylinder block to select the correct thickness head gasket.

There are 3 thicknesses available

1 Notch is for piston projections of .66 to .86mm, gasket is 1.53mm thick.

2 Notch is for piston projections of .87 to .90mm, gasket is 1.57mm thick.

3 Notch is for piston projections of .91 to 1.02mm, gasket is 1.61mm thick.

Thanks. I'm not sure if the correct gasket was used i'll have to check it out, though it wouldn't surprise me if the wrong one was used . I think theres been a few bodged repairs in its life with previous owners. I'm gonna rebuild the engine and replace the cylinder head as its also damaged down one of the injector seats. I just hope theres no damage down the bottom end of the engine as its been hitting the valves, fingers crossed....

Thanks again,

Rob.

After a 'rebore', the engine will need 'oversized' pistons and rings.
If the head is 'complete' and comes with valves/followers & camshaft it should be correctly shimmed 0.2 - 0.3 for inlet, 0.4 - 0.5mm exhaust but......this should be done hot so the adjustment will be rough and will need re-checking and shims replaced anyway... usually after a thousand miles....

Martin

THanks for the advice Martin, appologies for the late reply just been away for a week, a lot of stuff to be cracking on with now!