spives

Hi everyone. I'm in the process of refreshing my ~200,000 mile M44/52 block. The bores are in fantastic shape with no scoring or scratching. From what I've read it is best to leave them alone if this is the case.

The pistons aren't so good. They collided with the valves after the timing belt let go. Since they all suffered some fairly deep cuts / dents my plan is to replace them. Wossner is an attractive choice given the reasonable price and alusil compatible skirt coating.

Should I be OK dropping an off the shelf set of 100mm pistons in? My block and original pistons appear to be tolerance group 1. This gives me a slightly larger bore which may be good considering everything I've read about coated pistons being a very tight fit in these engines.

Any wisdom from the experts? I appreciate the help!

blade7

No ridge 1/4" down from the top of the cylinder ? Wossners run more clearance than original pistons so I'd have your block properly measured before buying.

spives

No ridge at all. I am shocked at how great they look. I will be taking some measurements tonight to be safe.

I'm glad to hear that the Wossners run a slightly larger clearance than stock.

333pg333

I'd be half inclined to see if your stock pistons can't be cleaned up and re-used. 200k is nothing to sneeze at with perfect bores.

Tom M'Guinn

I'd get a bore gauge. Smooth bores can still be out of spec, and plugging any piston into an un-machined 200k bore is like rolling the dice if you don't measure everything out. While tedious at times, getting clearances right is a big part of what engine building is all about... Just say'n...

spives

Yeah? I did consider this, but the gouges are fairly substantial. I know it's OK sometimes to clean up the high spots and reuse them but in this case I wasn't sure I wanted to risk the possibility of creating hot spots and making detonation more likely. I have reused pistons like this in the past but only in NA engines.

My other concern is the original iron coating on the skirts. I made a point not to scrub on the skirts when I was cleaning the flaky carbon off of the tops of the pistons, but I'm feeling slightly paranoid now that I could have compromised what coating may be left.

Would having the old piston skirts coated be a practical solution assuming they don't have any damage and I can clean up the damaged areas?





If it makes any difference, I am building this with the intention of making around 300whp and taking it out to the track maybe 10-12 days a year. Charlie at Evergreen is building me a K27/K26 hybrid and I'm about finished assembling my MS2 v3.57. The clutch is all new with a Turbo Cup disc and the rotating assembly will be balanced as soon as I've got the pistons figured out.

michaelmount123

Those pistons are worn out! A good ring groove/ring seal went away long ago. It's a good time to freshen the head too. The valve guides will be well worn.

333pg333

Errk...yep!

spives

Right, I figured the pistons were probably throw aways.

The head is being rebuilt as we speak. All new valves and guides.

V2Rocket

...so did you go with Wossner

spives

I did. Quality looks good and they measured out very consistently. I think they will work well for this engine.

Of course I've already started dreaming of building a stroker... haven't even driven this car yet!