Do you know how to use MsExcel? You need to build your self a little spreadsheet to calculate the piston height in relationship to the block deck. You can do it by hand, but having the spreadsheet makes it easy. If you e-mail me direct I can send you a spreadsheet that is set up (for metric engines), you just have to plug in relevant information.
Basically what you need is the following information for all the different parts from different engines:
1. the block (crankshaft center to deck distance)
2. Crank center to rod bearing center distance. This = 1/2 stroke
3. Rod length - center to center (measure the two holes and the distance between the close edges, so rod length = (Diameter#1 + diameter#2)/2 + distance between
4. Piston height -Piston Pin center to piston top distance.
5. head gasket thickness when installed -crushed. You can measure the fire ring on an old gasket to find this.
go search the web for that information on each of the two engines, 2.8 and 3.1, its probably available.
Additional information that is useful is piston dome or dish volume (cc), and head chamber volume (cc). you can use that info along with the other measurements to calculate engine volume and Compression Ratio (important!)
This works easy for flat top pistons. If you have domed pistons it might give you a bad answer, so you'll have to do a second measurement. What you want to calculate is:
head gasket + Block height (Crank center to top deck) minus [ crank throw+ rod length+ piston height]. That should equal a positive value meaning the piston is below the block deck and it won't hit the head. Negative implies your pistons will hit the head.
If you have domed pistons and you get a negative value in the calculation, then you need to remeasure your piston, and the head. Measure piston pin center to the flat part of the piston top, and the calculate the height of the dome. then measure the depth of the head chamber. This is going to be difficult since you have to figure out where the dome will be closest to the head. Use the pin to flat part number and calculate vs. the block height, it should be again positive, meaning most of the piston is below the block deck. Then subtract the piston dome height from head chamber depth and see if that is also POSITIVE. a negative value implies your piston will hit the head chamber
Or: find another GM engine that will bolt to that transaxle and swap it in.
Or bolt in a motorcycle engine and figure out how to make that work with your GM transaxle.
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