Some pics of 308 bottom end after 100k and piston check

There was a 100 deg day when a guy with a new 997 turbo chased me up the moutain and my oil temp was 250-260 and water was probably 240 . .. I think things grew a bit during that stint Next time I'll have a boroscope and be monitoring it. So the scratch above the ring line is where a chunk probably got thru?

Also, all of the above issues your mentioning have happened at one time or another dialing in the new fuel injection & timing with the high comp pistons. This motor is back in my car right now and is the one that made 210 hp at rear wheels so it's not hurt too bad . .. I'll leak that cylinder down and see how much worse it is now than the others . .. from memory was only 1-2% more leakage.

 

Just checked the top ring groove on the stock pistons and it's .0015 clearance on the land so really no wear here ... end gap was .004 big though. Maybe the 911 engines you've worked on actually saw more track days

 

Stock pistons?

 

Not that obvious in the WSM.

First, the 4V sleeve is tapered .0005

Then I didn't see an actual piston to bore clearance called out, but piston dia metric is 80.923/80.947.

2V stock clearance is .02/.06 mm, max being .1 mm . .. might apply to 4V or it's just buried deeper in manual verbage. I'll look again later if you don't get a better answer.

 

These two were closer two .004" clearance . .. blurred one is #8 on same bank. Think I'm going to just bore this next sleeve set in my fixture with at least .004 clearance and make sure this problem doesn't recurr before worrying about .002" distortion from head tq.
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That's one of these motors with forged pistons? If so was that clearance with the sleeve out of the block? Also heard JE don't grow as much as Wiseco . .. these are Wiseco . .. next sets JE . . . what are yours?

This motor's experienced more than one "bad tune" condition . .. once I get it apart again be able to show you guys more.

When I've been tuning I've relied on a wide band mostly for A/F ratio . . . there's a thermocouple input available . .. would this tell me a lot in the future to prevent this from happening and/or fix it if there's still a problem? Unfavorable conditions are you going to see an increase in exhuast temp? Right now there's partial throttle conditions where it's still real lean . .. didn't think it mattered too much under these lighter load conditions . .. thoughts?

Thanks,

Sean

 

Chatting with sleeve Steve earlier I understand more now how the top of the piston can grow significantly more than the skirt. Never had to think about that

I couldn't stop staring at the localized inteference above the top ring only on the intake side . . . no problem on the exhaust side . .. staring at it pacing around the living room it occured to me maybe the thin cross section of the piston in that area that Ferrari cuts away is getting way too hot. That is a real thin cross section on this set of pistons . .. will know when I tear it down. The fact that the exhaust side didn't show the same wear made me think the problem was localized some how . . . being on the intake side I would have thought the incoming fuel would cool that side of the piston a little more than the exhaust also.


Thoughts?

 

Piston maker recommended .003 by email and .0035 on spec sheet.

I would say they all show it to a slight degree with the cylinders that had almost .004 clearance way less . .. exhaust side not showing problem at all . . wouldn't this side of the piston be hotter?

I doubt manufacturer could tell me anything 'til piston was out, but be worth sending them a pic .. . I really think that thin cross section around the intake valve pocket has something to do with it.

Fact this isn't on the exhaust side of the sleeve isn't telling anything?

 

You run tighter that what the piston manufactuers call out for?

On both set, JE and Wiseco, they called out for .0035 on the spec sheet.

My map if anything was way rich at first . ... you think there's anything to fuel washing oil away?

Without seeing the actual piston, I know it's speculation, but you're thinking the scuffing is happening at the top of the piston due to excessive head temp not the skirt? If you've seen this in the past did you see it isolated like this . . . something to do with wrist pin offset so the pistons always "cock" one way so rubbing starts on one side only?

You don't think that thin cross section by intake pocket would create a hot spot? Ferrari trimmed this away.

Thanks much for the input,

Sean

 

Yep . . . it's back in right now running with stock cams and valve train . .. 50 hours so far with no problems but with stock valve train I'm not goint over 7700 rpm . .. was going to 8300 before. I wish I had a boroscope to look down in the cylinders to see if it's continuing to detoriate . .. need to get one.

Not to get off topic on the shim issue, but cam failures are not as uncommon as I was originally led to believe . .. still not convinced it was lack of spring pressure causing valve float but that and lack of zinc in the oil is an easy answer . . . . got a couple different cam guys looking at this stuff one last time . .. not the people that make the cams . . . independent opinions.

 

I was really trying to watch things i.e. pulling plugs etc. to see what kind of damage the detonation was causing . .. at one time I saw a few AL specs on the plug and could see a little bit of carbon had been blown off the tops off the pistons. I've heard pinging plenty of times since then on crap gas when I've not added race gas or anything . .. always pulling the plugs out trying to gain knowledge, and have never seen specks on the plugs like I saw when initially tuning and sorting things . . . made me think I wasn't hurting things anymore.

When I had the heads off the motor there was no signs of detonation/heat on the crowns themselves (no pits).

edit: don't think anyone really knows what happens when it's warm . . . getting tempted to run hot water thru the block to see . . . pretty sure it grows even more in this direction when it's warm based on what I saw trying to simulate the distortion in my fixture.

 

20/50 Castrol . . . I thought "they" had stop putting zinc in the oil due to catalytic convertor damage? regular non synthetic

 

Thanks for the insight.

Will post pics of the pistons when I pull her down.

Sean