Bore and piston wear boosted aplication
Discussion
Hello all!
I'm new here. A couple of years back i restauraten my car and supercharged it (eaton m62 blower at 10psi). Original it got 189 crank HP. Now it is at 310hp and 420Nm. It's an alfa 75 3.0v6 12v (1989). I rebuilt the engine. Now, 6000 miles on the rebuilt engine, i wanted more power so i decided to lower CR (was still original 1:9.5) so i could advance more timing. It was a knock limmited timing table. When i pulled the heads to mount a thicker headgasket i was disapointed to see there was a lot of wear:
I drove the car hard after a good warmup of course. It also saw some trackdays. But in my opinion this is exesive wear. No overfueling. I ot a wideband installed.
From my opinion the piston crown has a lot of carbon buit up. Has the carbon scuffed the cylinder walls? Or is this wear to distortion of the piston. It still has the original cast pistons.
Hope you guys can help me out!
I'm new here. A couple of years back i restauraten my car and supercharged it (eaton m62 blower at 10psi). Original it got 189 crank HP. Now it is at 310hp and 420Nm. It's an alfa 75 3.0v6 12v (1989). I rebuilt the engine. Now, 6000 miles on the rebuilt engine, i wanted more power so i decided to lower CR (was still original 1:9.5) so i could advance more timing. It was a knock limmited timing table. When i pulled the heads to mount a thicker headgasket i was disapointed to see there was a lot of wear:
I drove the car hard after a good warmup of course. It also saw some trackdays. But in my opinion this is exesive wear. No overfueling. I ot a wideband installed.
From my opinion the piston crown has a lot of carbon buit up. Has the carbon scuffed the cylinder walls? Or is this wear to distortion of the piston. It still has the original cast pistons.
Hope you guys can help me out!
You say wear ?
So you mean the bore and piston no longer measure to spec ?
It's maybe seen some heat, big deal, nothing major. Bore Hone marks look a bit weird though as if done some strange way ?
Crap on the top of piston could be any number of things, so without full details of the build and any crankcase breathing arrangements etc...means nothing.
Photo of the top ring looks a bit odd, but hard to tell when can only see a small portion of it.
But why is the engine apart now ? Are you implying there was something wrong that lead you to take it apart ?
So you mean the bore and piston no longer measure to spec ?
It's maybe seen some heat, big deal, nothing major. Bore Hone marks look a bit weird though as if done some strange way ?
Crap on the top of piston could be any number of things, so without full details of the build and any crankcase breathing arrangements etc...means nothing.
Photo of the top ring looks a bit odd, but hard to tell when can only see a small portion of it.
But why is the engine apart now ? Are you implying there was something wrong that lead you to take it apart ?
stevieturbo said:
But why is the engine apart now ? Are you implying there was something wrong that lead you to take it apart ?
Have you read his post?It's been burning a lot of oil I can see that.
A thicker head gasket IS NOT the proper way the decrease the CR, it's a bodge.
Buy some measuring equipment, strip it and check everything is in tolerance, it could be one of many things.
Yes, the pistons were coated to fit the enlarged liner bore from honing. You can see trough the coating now... it has a piston to wall clearence of 0.12mm now and it should be no more then 0.06mm according to the specs. And it was 0.06mm after the rebuilt.
Crank breading was not the best. It was a the small original oil seperator no bigger then an espresso cup ( italian style
) i upgraded it to a better and bigger format 500miles back or so but i think harm was done already...
What do you mean with strange hone pattern? I see the pattern is gone on the thrust side.
Crank breading was not the best. It was a the small original oil seperator no bigger then an espresso cup ( italian style
) i upgraded it to a better and bigger format 500miles back or so but i think harm was done already...What do you mean with strange hone pattern? I see the pattern is gone on the thrust side.
Gtv-racer said:
Yes, the pistons were coated to fit the enlarged liner bore from honing. You can see trough the coating now... it has a piston to wall clearence of 0.12mm now and it should be no more then 0.06mm according to the specs. And it was 0.06mm after the rebuilt.
Sounds like a high quality job 
What did you do about the piston rings?At least now you can do the job properly, buy some new low comp forged pistons, re-bore, have the rest of the engine checked out etc before rebuilding.
stevieturbo said:
227bhp said:
Have you read his post?
Yes, and there was no reason to strip the entire engine down.Gtv-racer said:
i wanted more power so i decided to lower CR. When i pulled the heads to mount a thicker headgasket i was disapointed to see there was a lot of wear:
Gtv-racer said:
No vertical scretches at all.
The reason for coating the pistons is that the built had to be cheap back in the days. Didn't want to spend a lot of money on the engine.
Now i'll do it right.
Any pin pricks on the top ring land? If not then I agree with Mignon that some dross has found it's way into the engine. If you have scores or pin pricks in the upper ring lands they you've probably had some detonation issues.The reason for coating the pistons is that the built had to be cheap back in the days. Didn't want to spend a lot of money on the engine.
Now i'll do it right.
227bhp said:
stevieturbo said:
227bhp said:
Have you read his post?
Yes, and there was no reason to strip the entire engine down.Gtv-racer said:
i wanted more power so i decided to lower CR. When i pulled the heads to mount a thicker headgasket i was disapointed to see there was a lot of wear:
Really from pics shown, there isnt that much of concern at all. At at 9.5:1 already stated....for a low boost setup I'd have little inclination to even consider lowering the CR.
I decided to pull the motor when i saw the cylinder marks. I lifted the head to lower cr.
These engines don't have a squish area so that's the reason for a thicker headgasket.
Top ring end gap 0.7mm
Midlle ring 0.7
Oil 0.82
0.55 is max for all rings, according to the manual, but i took some aditional play becuase it came as an NA engine from the factory and now it is supercharged. Don't know anymore where i sat the play. Obviously there is also a little wear.
I also see some piston rock not much . The skirt is a bit convex.
These engines don't have a squish area so that's the reason for a thicker headgasket.
Top ring end gap 0.7mm
Midlle ring 0.7
Oil 0.82
0.55 is max for all rings, according to the manual, but i took some aditional play becuase it came as an NA engine from the factory and now it is supercharged. Don't know anymore where i sat the play. Obviously there is also a little wear.
I also see some piston rock not much . The skirt is a bit convex.
My tuners sad the timing table was knock limited and i know some guys who lowerd compression saw 350hp instead of 310hp with the same engine.
These engines had 9.5 to 1 because in the days they where built that was the max cr they could run with these engines in my opinion so a litle cr drop isn't that strange i think.
Crank bearings which where fine before rebuilt still look nice. But some are bad. They where not in the best shape last time i saw them. I need a regrind.
Top ring lands look very nice.
I just saw some coating fractures near the top at the oil ring where the coating starts. I think the scuffing is from coating particles.
The coating should be bullit proof according to the company.... but it isn't..
In dirt particles i don't believe. I washed the engine over and over with solvent and flushed all oil channels. I worked realy clean.
These engines had 9.5 to 1 because in the days they where built that was the max cr they could run with these engines in my opinion so a litle cr drop isn't that strange i think.
Crank bearings which where fine before rebuilt still look nice. But some are bad. They where not in the best shape last time i saw them. I need a regrind.
Top ring lands look very nice.
I just saw some coating fractures near the top at the oil ring where the coating starts. I think the scuffing is from coating particles.
The coating should be bullit proof according to the company.... but it isn't..
In dirt particles i don't believe. I washed the engine over and over with solvent and flushed all oil channels. I worked realy clean.
They do have a squish bands, it's very rare any engine doesn't. It's that band around the circumference. If you use the 
method with a thicker gasket you'll have less mixture motion and less detonation resistance which is the opposite to what you're trying to achieve.
With the amount of oil its been burning its also more prone to det' too as it brings down the octane rating.
method with a thicker gasket you'll have less mixture motion and less detonation resistance which is the opposite to what you're trying to achieve. With the amount of oil its been burning its also more prone to det' too as it brings down the octane rating.
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