Sharp Piston Edges

[Joryn]

Hey all,

Discovered an interesting problem on my wiseco pistons when I had to change the headgasket for the second time due to another blowout. I noticed that on #3 and #4 cylinders the pistons in a couple locations right at the cylinder wall had sharp jagged edge on them. ON #3 it was about 1/4 of the bore and on #4 it was for a bout 1/3 of the bore.

I believe that these ridges might be causing hot spots in the combustion chamber and causing preignition which has caused the 2 recent head gasket failures but I can't say that I've heard of this particular problem much before. I was hoping someone on here might have more experience with it.

Also if it is the cause is there a way to fix it? (assuming pistons are otherwise in fine shape). It should be noted that my compression on these pistons was very good (~120) and so I don't believe that the pistons are destroyed yet. Is it possible to just get the edges sanded down to be smooth again (at a machine shop preferable to maintain balance) or are these practically brand new wiseco's now toast? I just got them in july

I'm hoping someone can give me some good news here heh. It's been a rough past while in my world of TD's so any info you can lend would be great.

Thanks,

Joe McDonald
1985 Dodge 600
2.2L Converted TII
Best ET: 14.54@86 mph
Best Trap: 14.71@93 mph

[Joryn]

*Bump*

Has noone seen something like this before?

[B.A.P.]

got any pics of the 'sharp jagged edge' ?

[Ondonti]

sharp edges on pistons do cause hot spots and furthur problems. Most piston machinists just dont put effort into making a decent piston a good piston.

All sharp edges on pistons should be laid back or at least have a tiny radius on them.

[Joryn]

Sadly no pictures as of yet. When I noticed them originally I needed the car up and running ASAP and didn't have time to take some nice shots. I could probably whip up a paint version though lol.

Assuming that the pistons are fixable what woudl be the best bet? Do it myself then? ie: could i just sand them down, as the edges aren't more then a a milimeter or two high and not extensive around teh bore. But I could potentially lose a gram or so in weight. that is my biggest concern really, throwing things off balance.

[Frank]

you wont through things off balance. get pictures for us. if not, you could just take a dremel and do it anyway. keep a vaccum up close to the dremel or sander to suck away debre.


frank

[89daytonaTII]

The small sharp edges are on the very outer lip, the cyl. walls in the coresponding area's didn't look to good either. Looked like the piston lip had been scored from contact with the cyl. wall on the down stroke raising a small edge on the piston. Left them both worse for wear.

The engine had less than 1k Km on it (right Joe?) when I helped replace the HG. Must have been incorrect clearences / shody machine work, as that's all that I can imagine causing that much damage in so little time.

[Joryn]

Yeah, less then 1k is right. I'm not sure what the cause of the cylinder wall damage was, as it wasn't so much damage as it looked like the hash marks had been worn right off in a few places. Interesting I thought cuz I checked the compression after putting the head back on and it was 120 across the board, even on the "bad" cylinders.

To really get the pistons cleaned up I would have to pull them out of the cylinders. As ryan said its on the very edge so pretty tough to fix, even at top dead centre. Seems my main questions have been answered though. If the piston is not otherwise damaged sanding off the jagged sections won't cause any balancing problems. At least that's what I've gathered thus far. I just thought it rather unusual that I've run into something that hasn't been reported much before. Unfortunately I'm not sure when I'll be able to get the head off and therefore pictures taken for a little while here. I'm still in the process of trying to find a replacement car for my girlfriend, plus my daily driver now has bad valvetrain noise so car wise I'm in a predicament.

Speaking of which hey ryan, want to sell the red daytona? hehe, I'll give you a lot more then you paid for it And barring that if you come across another deal of a similar natre Plz let me know. I've been looking for 3 weeks now and have found Nothing even remotely a good deal in the 1500 range

Thanks all for the help, as soon as I get pics they'll be up here.

[89daytonaTII]

That's a tempting offer, but I just can't subject the Shelby to being driven around at this time of the year. I'm always looking out for those good deals, I'll definitly let you know if I see another one.

If you need any help you know where my garage is

[dodge80_89]

Hmmm, sounds interesting, my 16v Wiseco's I just got in all had sharp edges on them. Especially around the top end AND where the valve reliefs were. Didn't know if this was common or not, wonder if my machinist knows. I don't want these pistons to turn into scrap after waiting 32 weeks to get them.

[Joryn]

Well sharp edges are a given, but these were jagged, definitely looked like detonation or preignition caused some slight piston damage on the crown on the bore edge. Although from what I"ve read it's not a bad idea to smooth out edges like that to aid in preventing Preignition anyways.

[Reaper1]

I always take the time to "soften" my pistons. It doesn't take that much time and is worth the effort IMHO....

[psychopjv]

you said the cylinder walls don't look to healthy.....sounds like piston slap if ya ask me.

[glhsken]

Quote:

Originally Posted by psychopjv you said the cylinder walls don't look to healthy.....sounds like piston slap if ya ask me.

I was thinking the same thing. Is it possible the bore tolerances were on the loose end causing (too big) causing the issue??

[Joryn]

That's entirely possible, although I did get the short block assembled at a machine shop. Originally I had intended on boring the block 0.030" (currently at 0.020") with a set of wiseco's to match but TU accidently sent me the 20's and Chris wasn't sure when he would be able to get 30's. So I took the pistons in and gave the shop the spec sheet and asked if everything would work and they assured me it would. Course They could be wrong.

If I was looking at piston slap what are some other signs that I could look for that would confirm/deny the problem? One thing to note is that the problem is only on 2 cylinders, coincidentally the 2 leanest cylinders (3 and 4).

The cylinder wall damage was basically sections of cylinder where the hash marks had been worn away but something riding on it. If this is a symptom of piston slap then I'm probably going to lean strongly in that direction.

IF that is the problem, what are the odds that something that I did would cause that problem? ie: is it possibly or even likely that the shop didn't read the specs correctly and put it together regardless? That opens up a whole other can of worms ....