I am putting new pistons into my motor after a valve went through one. I am just about ready to assemble it, but wanted to plastigage the rod bearings, but can't find any post about what size plastigage to buy, and what the width should be after torquing down the rod ends. I have the old bearings, which I think are ok, but just bought new ones since they are in-expensive and cheap insurance.
Also, anyone familiar with how to measure the piston to bore clearance? Wiseco says that should be 0.0030 of an inch. a type of feeler gauge?
VTLoki wrote:I am putting new pistons into my motor after a valve went through one. I am just about ready to assemble it, but wanted to plastigage the rod bearings, but can't find any post about what size plastigage to buy, and what the width should be after torquing down the rod ends. I have the old bearings, which I think are ok, but just bought new ones since they are in-expensive and cheap insurance.
Also, anyone familiar with how to measure the piston to bore clearance? Wiseco says that should be 0.0030 of an inch. a type of feeler gauge?
The new width will depend on the plastiguage used, but it should come with the numbers. The clearance you are looking for :
rod bearings: 0.00098-0.0031 in
main bearings: 0.0006-0.0019 in
These are GM specs from the NY-jbodies library, now hosted on Kardain's site
here
Piston to bore clearance, as I assume at least, measure bore diameter, measure piston diameter, subtract
You should measure in multiple spots for each value, and average.
fortune cookie say: better a delay than a disaster
this definately helps me out a ton too! i'm just gettin ready to put my new crank in and was wondering what the clearances were myself. thanks for helpin us both out!
OHV notec wrote:VTLoki wrote:I am putting new pistons into my motor after a valve went through one. I am just about ready to assemble it, but wanted to plastigage the rod bearings, but can't find any post about what size plastigage to buy, and what the width should be after torquing down the rod ends. I have the old bearings, which I think are ok, but just bought new ones since they are in-expensive and cheap insurance.
Also, anyone familiar with how to measure the piston to bore clearance? Wiseco says that should be 0.0030 of an inch. a type of feeler gauge?
The new width will depend on the plastiguage used, but it should come with the numbers. The clearance you are looking for :
rod bearings: 0.00098-0.0031 in
main bearings: 0.0006-0.0019 in
These are GM specs from the NY-jbodies library, now hosted on Kardain's site here
Piston to bore clearance, as I assume at least, measure bore diameter, measure piston diameter, subtract You should measure in multiple spots for each value, and average.
Great. I was looking for the ny jbody site but it seemed to have gone done. Thanks for that link, and the information. I have a 95 2.2. Are these specs the same as the 2200 motor? I think they are, but just wanted to get your opinion.
Hold it... a catch for the piston clearance measurement. There is a specific place on the piston where it needs to be measured. The crown (top of piston, above the rings) is smaller and will always appear to have more clearance. If you're not using stock pistons you need to find documentation from the manufacturer to determine correct location. Also, quite often you'll need an outside mic to measure piston diameter at the desired location, and an inside mic or bore gauge to measure bore, then do math. Bore - piston diameter = clearance. Measuring with a feeler gauge can be really tough to get right.
Tried a quick search for pictures on the net, but no luck. Federal Mogul / Speed Pro might have more information in their catalogs.
-->Slow
slowolej wrote:Hold it... a catch for the piston clearance measurement. There is a specific place on the piston where it needs to be measured. The crown (top of piston, above the rings) is smaller and will always appear to have more clearance. If you're not using stock pistons you need to find documentation from the manufacturer to determine correct location. Also, quite often you'll need an outside mic to measure piston diameter at the desired location, and an inside mic or bore gauge to measure bore, then do math. Bore - piston diameter = clearance. Measuring with a feeler gauge can be really tough to get right.
Good call, I forgot to mention measuring locations. My piston crowns look like they have 1/8" clearance
And yes, always micrometers, never feelers for these clearances.
Slow, any recommendations for ring gap on our small turbo motors? I'm not using GM's specs, because I'd hate to lift another ring land
fortune cookie say: better a delay than a disaster
slowolej wrote:Hold it... a catch for the piston clearance measurement. There is a specific place on the piston where it needs to be measured. The crown (top of piston, above the rings) is smaller and will always appear to have more clearance. If you're not using stock pistons you need to find documentation from the manufacturer to determine correct location. Also, quite often you'll need an outside mic to measure piston diameter at the desired location, and an inside mic or bore gauge to measure bore, then do math. Bore - piston diameter = clearance. Measuring with a feeler gauge can be really tough to get right.
Tried a quick search for pictures on the net, but no luck. Federal Mogul / Speed Pro might have more information in their catalogs.
-->Slow
Yup, these are custom wiseco pistons. I had an old set, and i just put the new ones on top of the old ones, and it "felt" ever so slightly smaller. with my fingers. The transition between the two was not perfectly even. I really hope these new ones are not slightly smaller then the old ones. I don't want ant piston slap. I haven't had a chance to put the new piston in the bore to feel how much it moves. Worst of all, I can't find my dial caliper to measure anything. grrrr.
Anyone in the northern virginia area want to help a fellow j-body guy this weekend with some tools/measuring devices?
I am getting the plastigage tomorrow, and if all goes well, i will be re-assembling the bottom end on saturday.
The new ones may be a little smaller if you ordered stock size, as forged pistons will expand more than cast.
fortune cookie say: better a delay than a disaster
Notec, I see stock specs of .010" to .020" for the top ring and .012" to .0177" for the second ring. Aftermarket rings generally come with guidelines for adjusting gap for Nitrous or boost so you should consult those, but I'd likely set the top ring to no less than .018" and the second ring at .017". Tighter gaps are better for sealing, but I'm not able to draw on years of experience building ln2 turbo after ln2 turbo to say the engine will be ok with a smaller gap.
There are different compositions used for forged pistons. Some expand more than others and will require more clearance.
Dial caliper is a start, but you really need a set of mics. If ya wanna come up to NH I'd be glad to help.
-->Slow
Aiiyuh. New Hampshah.
-->Slow
Well, I was able to measure my old and new pistons with a dial caliper. Both measured out to the exact same size. Now, I had a question. When I slip the old piston into the bore, it is tight, and hard to spin or go up and down, but it fits. The new ones, fit in and move around freely, but doesn't feel as if I can move it side to side.
If my new pistons are smaller a few thousands, what kind of problems could that cause, and how much should I be worried.
I guess i might have piston slap, or burn oil quickly..?? Thoughts and opinions are welcomed.
Are you trying these without rings? The difference might be due to metallurgy of the piston. Excess clearance is no difference than a worn cylinder. You may get some noise on cold startup, but probably not much. Oil consumption depends on rings.
Here's an idea for ya. Grab a ring and put it in the bore. Use a piston to push the ring about an inch into the cylinder. The piston keeps the ring square in the bore. Measure end gap once the ring is installed. Remove the ring, install it in the piston, and comress it 'till you have the same gap. You can get a visual indication of clearance by looking at how much the rings extend past the piston.
-->Slow
Thanks, I could try that, but how am I suppose to compress the ring, and see how much it stands out? I have a ring compressor, but it is hard to see anything once it is compressed. I could try i guess. So far, i've got two pistons installed, and measured the clearance between the new rod bearings and the crank journals. I'm consistently getting between .001 and .0015.
So, everything there checks out. Also, there's some rust on parts of the top of the block, on the deck. What would you recommend to remove it? Lightly sand until it is removed. It's not a lot of rust, just a small layer on certain spots.
Use a big hose clamp. I've used 'em to compress rings at the track before.
No sanding!!! No wire brushes or Scotchbrite, either. The sand/ wire/ abrasive will end up in the block. Best method is 3M gasket remover disc. For a small spot try using a razor blade and live with whatever's left. If you're talking about very small amounts of rust, you might even be able to ignore it.
-->Slow
The gasket Remover Disk worked perfect. It kinda made a mess of things, and small particles went everywhere, but i should be able to clean it up so it won't do any harm to the engine when it first starts. Some fell down where the lifters and the cam is. I think i'll just pour some oil down there and wash the particles into the pan and drain it. I got most of it out of the cylinders and the top of the pistons.
All the pistons are installed, and all the rod bearing clearances are within spec. I rotated the crank a few times with the assembly lube on the crank to make sure it turned. It's pretty east to turn the crank, but gets hard i guess when the pistons are at tdc or bdc. Dunno. The only thing I needed to check was the rod bearing clearances right. What else before i seal up the pan?
Well, everything worked out. Got the car fired up last night, and everything ran fine. I'm so relieved, and glad to have the car running. Now, i just have to turn the three other seats in the car, back into passenger seats, and not car part holders. haha.
