Brat boy
Dirt Slinger
I want to bore a stock 79 650 engine. I need recommendations as to how big of a bore do I go. Looking more of durability than speed!
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Boring out 650
- Thread starter Brat boy
- Start date
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- Tags
- bore engine
From stock you then have .....1st oversize......2nd oversize......3rd oversize.....4th oversize. This is the standard for re-bores then new cylinder sleeves and start from standard 650 pistons again.
There are now larger over-size's. Heiden Tuning has a 6th oversize, (about 680cc), then there are 700cc kits. These can all be done on the 650 sleeves.
All should cover your duribility question.
Often when things are mismatched, like compression ratios are to high and the wrong pipes for jetting or having the wrong porting done. These are more of a running problem and probably wont affect durability.
Main problems for durability is having to much fuel or to little fuel. To rich washes the bore and to lean will hole a piston.
There are now larger over-size's. Heiden Tuning has a 6th oversize, (about 680cc), then there are 700cc kits. These can all be done on the 650 sleeves.
All should cover your duribility question.
Often when things are mismatched, like compression ratios are to high and the wrong pipes for jetting or having the wrong porting done. These are more of a running problem and probably wont affect durability.
Main problems for durability is having to much fuel or to little fuel. To rich washes the bore and to lean will hole a piston.
From what you are saying I would just go the next larger over bore to clean up what you have.
Take your pistons to a machine shop and get them measured. Use these numbers to determine the size, out of round and taper of the bore. Size and out of round on the pistons.
Your repair manual has the specs for these measurements.
If out of spec, decide just what over bore it needs. 1st, 2nd or whatever. Get new pistons and rings then take them to the shop and have the cylinders bored to match the pistons.
I had a set of cylinders that needed a first over but found a set of NOS second overs for about half the price. I went second over. The shop charged me $35 per hole for boring.
Leo
Take your pistons to a machine shop and get them measured. Use these numbers to determine the size, out of round and taper of the bore. Size and out of round on the pistons.
Your repair manual has the specs for these measurements.
If out of spec, decide just what over bore it needs. 1st, 2nd or whatever. Get new pistons and rings then take them to the shop and have the cylinders bored to match the pistons.
I had a set of cylinders that needed a first over but found a set of NOS second overs for about half the price. I went second over. The shop charged me $35 per hole for boring.
Leo
