What could cause the pistons to keep cracking?
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What could cause the pistons to keep cracking?
I'm so sick of tearing this engine apart because of cracked pistons! I theorize that the left balance shaft is the culprit. The reason I believe it's the left balance shaft is because I recall when installing it, it was very loose between the bearing. I'm wondering if I'm losing oil pressure because of the bad fitment between the balance shaft and its bearing and thus causing the pistons not to cool down enough. Thoughts?Quote:
Originally Posted by BJH324JH
Hey, BJH324JH...I'm no top-notch mechanic, but it occurs to me that WHERE the pistons are cracking would be an indicator. My thought when I read your post was that perhaps the wrist pins are bent. Again, I'm only going with gut feelings. Do keep us posted on what you find out.
I had taken the block to many shops because they failed to deck the block properly. Finally took it to a surface grinding shop and they got the job done. I wonder if it's too much compression because of the removed material on the top of the engine. I believe they removed .010".Quote:
Originally Posted by royster
Are the pistons cracking in the same spot? If so, where?
I'm not sure compression would crack pistons, but it seems to me they DO make a thicker head gasket.
Yeah, I'm not sure how close to the deck the pistons get with the stock configuration/parts, but milling too much off the deck might allow the pistons to strike the head. That last .010" shave would have been in addition to whatever the prior guys removed, maybe too much taken altogether.
A thicker head gasket might work, or I've even heard of folks doubling up head gaskets, tho' that can be a dicey proposition. Fel-Pro makes some copper or stainless shim gaskets designed to work together with a regular head gasket to reduce compression slightly by raising the effective deck height slightly; not sure if they or anyone else offers these for our engines, tho'.
I presume you used a new head gasket every time? I wonder if reusing a previously-installed gasket could compress it beyond a spec that would allow for adequate piston-to-head clearance.
If it’s done it more than once. It’s probably running way lean and overheating them.
How do your spark plug tips look? I'm betting white.
Agree with other lean diagnosis given the multiple decking of the head. If you're going to rebuild it again, new complete 4g54 heads are available and reasonably priced in Australia
, don't know if that's the case where you are.
Yes, I always used a brand new Felpro head gasket everytime. Wrist pins are brand new too. Cylinder Head is brand new. The pistons are indeed cracking in exactly the same spot every time. I used hypereutectic pistons and cast pistons and same thing occurs. Cast rings, and chrome rings too. They still crack. Oddly enough the rings themselves don't break. They are perfectly intact. Here is a picture of where the piston breaks everytime on all four pistons. They crack in that spot or completely just break out:
https://i.postimg.cc/FkvGdxbh/PXL-20...-165401763.jpg
So it's a land between ring grooves that always breaks off in the same spot? Just the one piston/cylinder, or all of them?
If it's just one and the same cylinder every time, I'd suspect the first piston to break there may simply have been faulty, but that break scuffed/wore/deformed the adjacent cylinder wall in a way that stressed replacement pistons in the same place, leading them to break there as well. In this case, you'd prolly need to have the cylinders bored out to restore uniformity of the bores, and get oversize pistons to match the new overbore.
It happens on all 4 cylinders.Quote:
Originally Posted by SubGothius
Look at these three links. They discuss piston land breakage, diagnosis and possible causes:Quote:
Originally Posted by BJH324JH
https://www.ms-motorservice.com/Medi...ying_51730.pdf page 34
https://www.engineaustralia.com.au/w...8/04/SB002.pdf
https://www.hotrodders.com/threads/b...-lands.497906/
The first thing to do is have the bore taper and size checked against the piston size. Because you can’t just shove any new piston into an unknown hole size. Then properly gap and space the rings. If they have too much play between the piston and ring that will cause it. Rings come in different thickness.
Thanks, I'll check it out.Quote:
Originally Posted by FMS88