I developed a knock, sounded like it was coming from the head. Removed and inspected the head and all is good, while the head is off (engine still in car) I had a look at the pistons and they also looked good. I touched the top of no1 piston and it dropped down about 2 - 3mm?. It all turnes over smooth from the crank, everything goes up and down as it should but it seems this piston is loose causing my knock? Anyone else heard of this? what would be the cause, surely not just loose rod bolts! Will I be able to check if I get the sump off ?

 

Did you just push down one side of the piston? They do rock in the bores a bit.

 

Nope, in the middle. Other 3 don't do it?

 

If you had 3mm of play in anywhere the engine would wipe itself out very quickly.. a slight top end knock is not that!

 

The engine would idle perfect, soon as I incresed the revs slightly it would knock like fooook! I had my mate check the head over and there is nothing wrong at all with it, it was only rebuilt around 200 miles ago. This piston must surely be the problem!

 

The piston acts as the small end bearing, they can wear quite badly & knock. Get the sump off, remove the big end cap & pop the piston out to check it.

 

If it were a rod end cap/bearing failure you would know about it as the noise would be very noticable and the rod would more than likely snap if you reved it hard enough.

It is probably the area around the little end pin not the pin itself. Maybe it has run dry of oil and f**ked itself. Ive seen an engine before that blew the head off the rod cap bolt, causing the piston to travel further up the bore an touch the head and valves (this was not known at the time). It went to an engine tuners for an opinion (Hitec in Cradley) where he revved the balls off it and blew it up on the spot, not good

 

Sounds like the big end shells have gone to me mate, whip the sump off undo the cap and have a look just to be sure!

 

That's what I'm trying to do but the starter motor's in the way and won't leave go!!!

I'll get there in the end! (hopefully)