I am working on an 04 LS6. When it had 50k or so it was rebuilt due to damaged pistons in a supercharged corvette. They replaced two pistons with LS1 pistons, cleaned up the affected head chambers, honed it and replaced rings and bearings (from what I was told).

I bought it at that point as a 0 mile rebuild. I put it in my truck and ran it 33k miles. Last compression test it made 175-180psi and ran perfectly.

I pulled it out of my truck and swapped some accessories, then dropped it into my 85 corvette. Everything was fine for a few hours, then it lost oil pressure. Apparently something must have gotten in during the swap, that wiped out the crank and bearings. So I am rebuilding again. It now has 85k or so total on the block. There is no apparent damage to the cylinder bores.

I'm trying to spec all the parts and figure out the best course of action.

I measured my pistons with an outside micrometer and locked in the measurement. Then I set my bore gauge to zero using the micrometer. Then I checked each bore to figure out the piston to bore clearance as it stands now.

I checked each cylinder bore in 4 places as viewed from above: horizontally near the bottom, horizontally near the top, vertically near the bottom, vertically near the top.

Here are my numbers.

CYL L-R BOT L-R TOP U-D BOT U-D TOP
1 .002 .0015 .0025 .0025
3 .002 .0025 .0025 .002
5 .002 .0025 .0025 .002
7 .0025 .002 .003 .0045
2 .0025 .002 .0025 .0025
4 .0025 .0025 .003 .0025
6 .0025 .003 .0025 .002
8 .002 .002 .003 .004

GM spec is .0007 to .0021. So all around I am out of spec with the current bores, and if I hone it even a little bit more I will probably be at least another thousandth (or more) out of spec.

What would be the consequence of running it this way? This is a street car with headers and exhaust and might see 3000 miles per year. If I did this I would do a quick hone of the bores, clean the block and other parts, replace the rings, and put it together with a turned crank and all new bearings.

For reference it ran great prior to the oil pressure issue and I would be perfectly happy with that level of compression and performance back now (with proper oil pressure). It seems like it was doing fine even though the PTB clearance is/was/has been out of spec.

Correct me if I'm wrong, but the alternative costs another grand or more for no real gain in performance, having it bored 0.010 over, buying 3.908 pistons and rings, and having to replace the rods (the mahle pistons apparently require aftermarket rods?).

Thoughts?

Thanks in advance.

 

You could save money by using stock rods and an oversize hypereutectic piston.

 

Thanks for the response.

Other than Mahle, what other affordable brands should I be looking for?

The reason I was looking at replacing rods is because the Mahle pistons I have been looking at in 3.908 all say they use a 6.125 rod, while the stock rods are 6.100. I am not sure why this is, or if I am just not finding the right Mahle pistons.

Another reason I was looking at replacing rods is that everybody on this forum swears up and down that the stock rods need to be resized for the ARP rod bolts I am using. I have to turn the crank at least 0.010 to clean up the grooving. So then I will have to find a rod bearing .010 undersize and .02 oversize at the same time. So far I have only found .02 oversize and .020 undersize.

It seems like by the time I get done paying for stock rods to be resized, I am only 300 bucks away from brand new rods.

None of the local machine shops I've spoken to inspire a whole lot of confidence in their ability or willingness to do this stuff, so that is one reason I'm trying to shy away from as many machining processes as possible.

 

It would be interesting to see what size a new stock piston measures? I'm wondering if the wear is more on the piston rather than the bore?
Only 2 of the bores look off much.

Have you looked at Wiseco pistons?

Scat makes a variety of good 4340 I beam rods with ARP bolts for around $330 a set. You will have to check the pin size. .947 is an odd duck, most all SB stuff is .927, so it seems like the aftermarket goes that direction.

I have been doing the same research for my 5.3.......it gets confusing for sure. New rods will require a rebalance as well.

ron

 

If you decide to get rods check out WS6store.com. i got scat Ibeams in 6.125 length for .927 pin and include ARP bolts for $280 shipped. Either mahle or wiseco would be your best bet. I got some Wisecos for $640 including pins and rings, kinda expensive but they are very nice and your pretty much set for spray if you want in the future

 

Well, my pistons measure .3895 which is right in the middle of spec. They (well, 6) are LS6 pistons with the skirt coating, which is still intact and not really scratched up much, so I don't think the pistons are worn at all.

No, I've searched ebay, summit, jegs, speedway, and the only thing that shows up for 3.908 pistons is various mahle kits. What other vendors do you guys look at?



I did not know that. What goes into a rebalance procedure? Are they simply weighing each component on an accurate scale prior to assembly and grinding material to make them all match weights?

 

.010 over Wiseco K398X3905

At Summit, just search for the part number. I've noted that they don't come up in a normal search.

Aftermarket rods are likely a different weight than the stock ones, so its the crank that needs rebalanced. The rods are probably weight matched to each other. a fussy machinest would get them all dead nuts.

You could just have your rods checked for roundness on the big end first.

Ron

 

Thinking further.......

You have 2 odd cylinders...perhaps the one that previously lost pistons? Bigger at the top than the bottom. So the piston will clearance at the skirt just fine.

So you are really only a thou or so from spec.
I'd hone it with a ball hone, they don't remove material, they just clean the bore. Put new rings in and call it good.
Have the machinest check the rod big ends, they might be fine too. I didn't see bearing wear that looked like the big ends were OOR.

If you bore, change pistons and rods, rebalance it's going to add up quick.

I've been back and forth on the same decision with my 5.3 thats going to get a turbo...finally decided to put it back together stock but clean. Otherwise, spend about 2 grand on the parts plus machine work....that I might blow up!


Ron

 

Another option would be to buy a new short block. You might be surprised how cheap a mostly stock rebuild LS1 short block cost.
Thompson Motorsports hypereutectic piston LS1 short block

 

I've thought of that as well. But I already have bought a lot of stuff for the rebuild, plus I have an aftermarket cam that I want to run again. And oddly enough I've built hundreds of rotary engines but never a piston engine, so I kind of want the experience and satisfaction of doing a build from the ground up. It'll open the door for me to do more cool **** later on.

However, in the unlikely event that I build this thing and it grenades itself again, I might just go the pre-built route so that I can finally drive the damn car after 1.5 years of delays.

Also, I do not plan for this to be my end-all-be-all motor. I just want to run it 2 or 3 years as is, and then probably go with a meaner, fully built big-cube LS motor like a 408 or LS7.

 

You don't bore a LS1 'You hone'

OP I went with Mahle 3.908 & Scat H/Beam rods

 

True, it's only .010" ,less on a worn bore.
Torque plates are a good idea as well.

Ron

 

From looking at the heads and from where the LS1 replacement pistons are in the motor, it looks like 5 and 7 took damage when it originally died at 50k.

I spent a few hours on the block. I went ahead with a new flex-hone 240 grit ball hone and hit all the bores with about 15-30 seconds of fast drilling. The way I figured it I'd do a hone and check the bores again to see if I can get by with the stock pistons. If so, great, if not, I haven't lost anything except my time since I'd still have to pay a machine shop to bore it and I'd have the experience of having done it.

I think I did pretty good for my first time and I am happy with what I see. I cleaned the block in my parts washer and blew it out with compressed air thoroughly and wiped it down.

I checked all my bore measurements again and it seems like I added between 0.5 and 1 thousandth to every measurement posted above. So I am now at 2.5 to 3.5 thou of PTB clearance everywhere except cylinder 7 which is 4.5-5 at the top.

I am leaning toward buying file fit rings and running it as-is with the stock pistons. I am okay with experimenting this way with a short-to-mid-term expectation just for the sake of experience, this is neither my daily driver nor the last engine I ever expect to put into it, and if I screw it up I should still have enough room left in the bores and crank to do it once more "the right way".

Here's one of my ball honed bores vs. one of the originals. What do you guys think of the bores now? You can faintly see some skirt wear below the crosshatch but I think that is okay.









Cleaned up block.








More of the bores and honing...

 

http://www.enginebuildermag.com/Arti..._finishes.aspx

http://www.enginebuildermag.com/Item...finishing.aspx

Good reading about honing.

Ron

 

Where did you measure the diameter of the Pistons for a baseline? Pistons aren't the same diameter from the skirt to the top (Just a thought).

 

Yeah, I figured that out when I was getting wacky numbers for piston diameter measuring at the top.

I measured them at the center of the skirts and got a perfect reading, so I have no doubts about that.

What I am more getting at with this thread is, can anyone say "I have built a motor with 3.5 thou of PTB clearance and had XXX happen" or "I have seen them built this way and they ran fine".

 

Bumping an old thread, maybe for someone else's benefit.

I built the motor in question with the stock pistons (I actually found and bought some more LS6 coated pistons so they would all match) and put it together. It's still together after a LOT of hell raising and trips to 6400rpm. Maybe 3 or 4000 miles total though. Doesnt use any oil or smoke in the slightest, runs like a new car. I do hear just a slight bit of tapping in the bottom end on cold startup for the first 30 seconds. but that's about it.

 

Holy necro-post Batman! LOL!
But good to hear it's holding together!