Hi, recently had a forged bottom end build, ie forged pistons, steel rods, race bearings, balanced crank etc etc.

The engine was lovely and smooth for the 1st 2000 miles, however after a 1000 or so more miles the engine developed a tapping noise so it went back to the builder (who have a very good reputation).

They stripped the engine and the only problem found was incorrect tolerence between the pistons and the bores, causing piston slap.

Can piston slap be cured by just fitting new piston rings or is a rebore to a larger size piston the only cure?

Also what is likely to be the cause of piston slap occuring after just a few thousand miles?

Any opinions would be welcome.

 

Does it happen when its cold and go away? Forged pistons do rattle around when they are cold.

 

It almost goes away when hot but not quite. Also there was no piston slap when the engine was 1st built and run-in, it is something that has developed.

 

I think that larger rings can be used if the bores are all still alright. Are they going to do something? Or have they done further work and the problem still exists?

 

No corrective work done yet, they are talking about using larger rings, but after spending over 12k with them altogether, I didn't want a bodge job done that might fail after the warranty runs out in a few months.

 

I would state your worry to the company. If they are, as you say a reputable company, you could ask them to increase the warranty if they are going to guarantee that this will fix it.
I think though that it probably will, it does tie in with what I would expect them to be doing. i would expect them to be doing it for no extra charge though, their first attemp didn't do what you paid for.
But, having said that I am not a mechanic by any means. It's just stuff I have picked up over the years.

 

That sounds like the way forward for me, I've been quite disappointed but your advice has made me feel a bit better, thanks JB1!

 

I am sure it will be sorted for you. They have their rep to consider. These things never go as smoothly as you want them to. I ended up waiting 12 weeks for a gearbox. But, my garage sorted it for me (was a 3rd party supplier that screwed up four times).
Just remain positive, always stay calm, and the garage will help you. If you lose it with them they won't want to go the extra mile to help you out. Always works for me.

 

I'm good at staying calm with them, they took 5 months doing the original job which they quoted me would take a week!

 

what pistons did you use? If they are cosworth you will get slap?

 

woosner pistons

 

changed the oil so the new stuff is different spec maybe?

 

Forged bottom ends are noisey. . . as long as it doesnt burn oil I would see how it goes. . .

 

Forged pistons do rattle, and do burn oil. If you are running big power then a little rattle is nothing to worry about. My own car did sound quite loud when cold, but its has got alot better the more I push the engine.