Alexandre: Now I get a much clearer picture of what you are trying to do with the 261 block. I've been thinking about the modifications you have mentioned, and been tossing thoughts around a little, and want to give you more imput.
I have sleeved many blocks myself. The standard sleeve set up involves boring block cylinder bore to within .250/.375 of bottom of bore, then stop! This "step", or ledge, is a positive register for the bottom of the sleeve to locate against. I like to keep the press fit on the easy side, say
0.0005/0.0007 inches, that way it will cause minimal wall distortion to block and adjacent cylinders. I always use locktite to bond the sleeve to block, then finish bore, then cut top down flush to deck. The head positively locates sleeve in place.
The 261 block does not have "much" of the bore or stock cylinder extending into the crankcase area. This means that for you to bore out that far (4.000), you will be well into the waterjacket
and will have no way to form a step or ledge for the sleeve. You will have to bore straight through (no material left) and may have seal problems in this area. Also without a register on the top of the sleeve, against the (counterbored)deck, you have no way to positively locate. How will you locate/lock in place? Also what does this "through bore" for the sleeve actually do to the blocks structural integrity? It will certainly not be as structurally sound or strong as an intergral bore block.
Offset grinding the crank to fit 292 rods.
Stock 261 crank pin is 2.311/2.312
Stock 292 crank pin is 2.099/2.100
The difference in pin diameter is .212, using 292 rods .106 offset from TDC stroke. No gain over stock 261 stroke of 3.940. The grinding will in effect make the pin diameter smaller, which will decrease bearing speed, but at the same time give up how much structural strength in the crank. The 261 crank already flexes with a larger pin diameter, and a larger, stronger, stock rod. The stock 261 rod lower end is larger in diameter than the 292, and is also wider than the 292 rod, so the impact/rod thrust load surface area is much greater with the 261 rod on the crankpin.
And what about this width issue?
The 261 rod width (OAL) is 1.242
The 292 rod width (OAL) is 1.030
And the bearings?
261 rod bearings are 1.033 (OAL)
292 rod bearings are 0.842 (OAL)
The narrow 292 bearings means that you will have to grind narrow offset on crank pins to fit, with smaller fillet radius of 292 bearings.
What about all the thrust on such a small bearing surface?
What about rod side flex and control, considering a portion of the radius, (TDC) will have no shoulder, or fillet?
What about oil control/throwoff?
I realize all these problems exist because of the differences, in the 4 or 7 main bearing cases, but this is the kind of problems you are going to run into.
You said you wanted to use 283 flattops. They will fit the rods, but I think you will have some other troubles here also. Need to check these exact block measurments, but I feel that the 261 is quite a bit taller block from crankshaft centerline to deck surface.
Stock 261 rod 6.8125 CtoC
Stock 261 crank has 3.940 stroke
Stock 292 rod 6.7660 CtoC
Stock 292 crank has 4.130 stroke
0.190 difference in stroke
0.0465 difference in rod CtoC
Compression height of these pistons (261 versus 283) are considerable. I think you are going to be a ways down the cylinder, and quite short.
Going to a smaller, lighter, piston certainly has weight saving advantages, but you may run into some control problems to.
With a 292 rod on a 261 crank and a short slipper skirt piston like the 283, I feel you will have rock/slap troubles, especially near BDC/TDC with compression and will have ring flutter or loss of ring seal. Stock type 261 piston is tall full skirted, and has less tendency to tilt/rock. More stable piston in a tall deck block. Also stock type 261 piston has wider top ring than 283 piston
and you already know the top ring does 90%+ of sealing of compression.
Anyway, I do not want to discourage you, or your experimenting. I think it's great! Thats how the neat stuff in modifications is figured out, with guy's like yourself pushing the envelope! I hope anything that I may have said, helps. Keep posting, and tell us of your trials!
Think Chevy!
:rolleyes:
