Tom M'Guinn

DHC8FO -- welcome to rennlist! Many people in your shoes just go out and find a replacement block or motor. You can over-bore and resurface the block, but oversize pistons are hard to find and expensive (as you know).

Porsche-O-Phile

I second that. The advantage to oversized is you can get more performance out of the engine and still boost it if you want, but it's going to cost a FORTUNE - oversized pistons alone I think are in the neighborhood of 1500 bones!

If it's going to be a *****-out race car, I'd say sure - give yourself every advantage you can - take the time, spend the money and go crazy. Otherwise, just get a replacement engine. Shortblocks can be had from $200; longblocks I've seen as cheap as $500.

dom1102

Hi, does anyone know the correct piston ring specification for Alusil bores? I have just had a 951 engine rebuilt using JE pistons and rings. The engine has done 2k miles and already has significant bore damage. The parts were specced and rebore carried out by an Alusil block specialist (Goznays UK), who assures me the correct process was used and the correct JE parts used. The guys who put the engine together (Promax UK), tell me the JE rings were the incorrect spec for an Alusil bore. Side note; the engine was carefully run in for 1k (of the 2k miles) on mineral oil. The oil was then changed for royal purple synthetic oil and the car driven normally. As soon as I started using it normally (full power), it was evident that there was excessive breathing from the engine. I am willing to accept that there might be another issue if the rings are not to blame. There is so much misinformation re Alusil so I am looking for a response from someone with qualified experience to help me try and figure out what has gone wrong here.

Jim @ EuroWerks

I don't want to waist your time with any of my theories and I could go on about them. However, I do know that the guys at Mantis racing in Canada do alot with over bores on these engines and I definately contact them and or JE dirrect. I am personally trying to be friends with JE rings and haven't succeded yet. Good luck.

BC

Were the pistons coated from JE? Or someone else coated the pistons? If you have uncoated JEs going up and down in an alusil bore then you will have a problem 98% of the time. If the pistons were coated properly with the correct material, then maybe the rings were wrong. The 951 uses, IIRC, iron rings. There is some sort of chrome face to the top ring, but the other compression ring is just iron I think. If the bores were not lapped properly with the pads and paste after initial boring, then nothing would have saved the bores.

dom1102

Hi, uncoated I think. Going to check and return with full piston and ring specs. I have to assume the block was properly finished, this guy prepares Alusil blocks for Audi.

whalebird

This is a good thread. I have a noisy wrist-pin and am getting ready to disassemble for repair. I have thought that I may need a new piston - I just don't know if the rod-bushing is all of the problem. So...Ihave been looking at the different options for pistons. My car is a street car and basically stock; I don't need anything fancy. I just won't know until I get into it.
FWIW, I have seen several problems with JE pistons in air-cooled applications.

Jim@eurowerks. As my repair progresses, I may need some machine work and parts. Any suggestions would be most helpful as I am in your area.

BC

The block could be properly finished, but if the aluminum pistons were uncoated and installed into the aluminum (alusil) bores, then that could very well be the problem. Even with enough lubricant, aluminum does not like to slide against aluminum. COATED JE pistons and rings have worked. I am almost 100% sure uncoated have not.

Olli Snellman

If pistons are uncoated.Do not start your engine.
I know several build ups with uncoated pistons (both JE & Wiseco) and all of these engines last about 30-50 km's....