stidi

Hi guys,

currently in the middle of my first engine rebuild (2004 LS1 from a GTO)

The engine was refreshed 6,000 with wiesco's, 243 heads etc and a few other parts. long story short the previous owner had an accident, front of the car ended up upside down in a ditch and had some water get in through the inlet.
this water sat there for about 9 months whilst the owner recovered and advertised the engine then I purchased it and had it shipped over to the UK. I've found the water sat on top of the pistons, behind the valves etc and I couldn't send it back due to the costs involved in transporting it i'd have lost $3000 in shipping and customs for nothing.

anyway, this was all a couple of months back, heads are being cleaned up right now (4 inlet and 3 exhaust valves needed replacing due to rust damage) the wiesco's should clean up ok (on the top) and though they have a few marks on the thrust side, they should hopefully be ok.

my main question is about the bores / clearances, I need to take the block to an engineering shop to get the bores honed as there was water in all the cylinders, this has sat for 9 months and basically rusted the rings and liners. I'm hoping a hone and new rings will be enough, failing that it'll be new liners or an overbore and new pistons it all depends on how much was taken off during the previous rebuild I guess.

right, with all the background out of the way my questions (thanks for staying with me this far)

the FAQ states "Bore Taper Thrust Side: 0.018mm Max. / 0.0007" Max."
does that mean if i run a bore dial gauge down the cylinder I'm allowed a deviation of .018mm / 0.0007" or am i allowed double that?

Piston to bore clearance 0.018-0.054mm/0.0007-0.00212"
again how is this measurement taken? can i have .054mm per side, or do I measure the piston and add .054mm / .00212" to that to give me my absolute maximum piston to bore clearance?!

following from the above, what sort of clearance can i have with Wiesco forged pistons? can i add a little more clearance at the top end because of the way they expand during warm up?

What's the largest clearance anyone on here has started with? at what point do Real users / engine builders say "right, I really do need bigger pistons now!" anyone run a .06mm clearance? 0.07? 0.08?!

being new to these engines and having very few resources in the UK for these engines is going to be a challenge, but hopefully you guys will have the knowlege i need! :thumbs:

Steve - Race Eng

iTrader: (1)

Give Mike a call at Boost Performance. Mike is very knowledgeable with LS based engines.

http://www.boostperformance.co.uk/

That said, the clearance measurements are the difference in diameter not radius for both piston to bore and bearing clearances.

Max. taper via GM is .0007" which is the max. variation you should see on your dial bore gauge, not double that. You should do this checking with honing plates bolted up.

Steve

KCS

iTrader: (20)

A competent machine shop should be able to get the cylinder taper down below .0007", it's not really that hard, unless it was REALLY bad to begin with and there wasn't enough material to hone out to correct the geometry. Hopefully, the shop that did the rebuild was competent enough to do so. If you want to measure to be sure, do so with the main caps and a torque plate installed and torqued to spec. I've always been able to get the taper down below .0005" on most of the LSx blocks, so I don't know how well it would run above that. Remember that every bit of taper in the cylinder will cause the rings to move even more, by a factor of pi (.0007" x 3.14 = ~.0022").

The GM specs are for the cast aluminum pistons that come in the engines from the factory. Those cast aluminum pistons are not nearly as dense as the forged aluminum pistons that companies like Wiseco sell, therefore, the cast pistons will expand much less and require less clearance while the forged pistons will require more.

Typically, a 2618 forged piston, like a Wiseco, will require about .004"-.0045" of clearance. To determine your piston-wall clearance, you will need to measure the diameter of the pistons and compare that to the minimum diameter of the bore. The difference is your clearance. You could probably still call Wiseco with the part number for your pistons (typically located on the top face of the piston), and they could provide you with all the info you need for those pistons, including recommended clearance and exactly where to measure on the piston (since you can't just measure anywhere on the piston to get the diameter).

I've seen as much as .007" run great in an LSX block, but that was in a 2000+hp drag car. I would recommend that you find out what you're working with right now, and go from there. If the geometry is good, and all you need is to clean up the rust, and restore the crosshatch, you can use a Flex-Hone type brush. It won't remove any significant amount of material, so it won't effect piston-wall clearance, but it also won't be able to correct any taper in the cylinders.

stidi

thanks very much for the info guys

a lot of the cost of the build is going to be determined by how good the bores are after a quick hone i guess (some cylinders were quite high up and some low down, obviously. so the amount of rust / surface deposit on each one differs, while there's no visible step, i'm sure that i must have affected the taper slightly, as were else has teh rust come from?)

hopefully most of the rust i saw was the valves and the liners are ok, but i won't know for a little while yet

stidi

I've measured the pistons and noticed that one bank has more wear on the thrust side than the other, so much so that the pistons are about .002" more worn (measured at the bottom of the piston, 1.5" from the bottom of the oil ring groove at 90 degrees to the pin, as per wiesco instructions.

is this common, or is there something wrong with my setup? :S

thanks again.

briannutter

Hi there, yes diamond turned pistons have a fine series of grooves in the skirts and the high ridges effectively wear down with that kind of mileage and stabilize when the lower parts of the grooves and upper match. The skirt coatings apply help with this. The pistons can be run at greater clearances .006 to .007 not a big deal at all and some have run a lot looser when trying to get every last mile out of their parts. You can also have "extra thick" layers of coating built up if you wish...we've seen it all feel free to PM me if you have any further questions. Brian Nutter -Wiseco Automotive

stidi

Thanks brian

I'll get some pictures and measurements up, there are also what appear to be Det marks on some (2 iirc, maybe 3) of the pistons. so I may have to buy a few individual pistons anyway.