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Well my first "Cheap" LS Turbo build has already hit a bump with having the pistons appearing to have valve slap.
The engine is a 2009 Gen 4 LH6 non VVT. We started to break it down to remove the DOD and prepare the motor for boost. When I removed the heads the top of the pistons had exhaust valve marks. The possible causes are loose/stretched timing chain, DOD miss fire or maybe over rev?
At this point after DOD delete, new timing chain, cam, lifter and springs need to know first how to address the pistons.
I just was going to inspect the bottom end, install new 3 bolt gear and chain and have the 799 heads rebuilt.
Any idea what can cause the custom exhaust valve and piston interference?
My $1800 budget is doomed if i have to rebuild the bottom end.
Here are some pictures
Do you know if the donor car was a manual or auto? If it was an auto trans, over rev is unlikely.
Is is it just a few pistons or all 8 that are marked. If it’s 1 or 2 I would be concerned for the rod bearings. Worn/loose rod bearings can allow the piston to travel up further just enough. If it’s all 8 then look at the timing chain.
I wouldn’t worry too much about replacing pistons as long as the gouging is shallow. But new valves would be cheap insurance now as the valve head is likely compromised from the contact.
If you choose to reuse the pistons, don't expect much out of them. Hyper/Cast pistons are rather fragile and the indentations made by an exhaust valve look pretty significant. If the budget is that tight, save up a few more dollars now for a set of pistons vs. spending A LOT more down the road when one of those pistons lets go and wipes out the whole engine.
Also, at a MINIMUM, the exhaust valves, pushrods and lifters MUST be replaced. There's no way in hell those valves are still straight, and the valve job is probably screwed along with them.
Thanks for all the feed back. We were told the engine came from a 2009 Trailblazer and was a LH6.
Now a after extensive late night internet trolling and a call to the Chevy parts guy it might be a LY5 for this LS doesn't have VVT.
Due to the odd casting numbers we just don't know where this motor came from. I'll be removing the timing cover and post a update on what we find. Any suggestions on OEM or aftermarket pistons?
With the sharp edge of the eyebrow the stock pistons could develop a hot spots. With forced induction that might be an issue. Others may say it's OK. All I know is being OCD, I'd want the eyebrow pistons replaced even just NA.
How critical is reliability? If it's a toy you could run it as is with the understanding that it may break. When it breaks get another junkyard motor. That seems to be what a lot of folks do.
Stock pistons have handled in excess of 1k hp on quite a few heavily boosted jy builds. Fragile? Not really. But youve got to keep them away from detonation and gap the rings to keep the ring lands happy.
We have factory replacements that are stock or over sized and will drop right in with a nice moly/steel ring setup.
For a JY pullout I would run those pistons as-is. As mentioned, you can always get another cheap pullout engine if this one grenades. Just know you’re likely to lose your cam and valve train if you’re putting extra money into those parts. I would clean the piston tops in place then you can stress relieve sharp edges with a dremel if you really want to be proactive. WS6 has a damn good deal too, can’t go wrong with new ones either.
Id be a lot more concerned with what allowed the piston(s) and valve to touch off though. With a stock cam and auto trans I can’t see over rev being a cause. Look real close at the valve springs if you plan on reusing, find a shop that can test them. If needed or just buy new take offs. Also I would check the rod bearing clearance on any suspect cylinders. You can do it with plastigauge while everything is still assembled. It’ll let you know if the clearance has grown and allowed more upward movement of the piston at the top of the stroke. It’s be better to find out before getting everything installed and fired up.
Stock pistons have handled in excess of 1k hp on quite a few heavily boosted jy builds. Fragile? Not really. But youve got to keep them away from detonation and gap the rings to keep the ring lands happy.
We have factory replacements that are stock or over sized and will drop right in with a nice moly/steel ring setup.
You gap the rings with boost of course. And throw some sand in the oil.
Filing rings with a hand filer then checking every so often with a feeler gauge and deburring evey single ring? Aint nobody got time for that.
Sometimes i type like i think. Sometimes i think before i type. I like to be surprised.
You gap the rings with boost of course. And throw some sand in the oil.
Filing rings with a hand filer then checking every so often with a feeler gauge and deburring evey single ring? Aint nobody got time for that.
Sometimes i type like i think. Sometimes i think before i type. I like to be surprised.
Thanks for all the input, I will be pulling the balancer this weekend and i'll post my findings. I like the run it till you blow theory for all the top end stuff can just swap into a newer short block.
I have to reminding myself this motor is going into a Volvo wagon!!
12-07-2018, 07:58 AM
Reuse pistons? 
