What's the acceptable tolerance for cylinder out of round and/or taper? Street motor. I haven't been able to find it in the literature.
Thanks
Cylinder tolerances?
Moderators: scottm, TrWaters, 392heminut
Re: Cylinder tolerances?
IMHO what's more important is piston/bore clearance, if you're getting a block bored/honed out, have them do it with a torque plate and get it perfectly round- if you're rebuilding and using the old pistons and just honing the bore to break the glaze, look at piston/bore clearance
regardless of what the specs say, you can go to .0035" piston/bore clearance in a worn engine, if you hone it and put new rings in they will take up the clearance- much beyond that and you'll get a piston slap with cast pistons- forgings are more forgiving and can expand more and take up clearance in the bore.
I have witnessed bullders go even further than that, who put rings on old pistons with .005" piston/bore clearance- the engine runs strong, doesn't burn oil, but has a faint "tonk-tonk-tonk" when cold, that never really goes away completely- one guy put rings on a Dodge engine that was .010" piston to bore, it ran good for about 10,000 miles, then started slinging oil all over the place from blowby
forgings are way more forgiving, I've seen another racer who would freshen his bracket motor every 2 years, just put new rings on the same forged pistons, and hone the cylinders again with a torque plate- eventually it was up to .013" piston/bore clearance and still ran in the 8's in the 1/4 mile, that was a 465 Pontiac with 13.8 CR in a tube chassis car that weighed 2200 lbs.- but that was a trailered car with a pan vac and vacuum pump, not a street car
what type of piston are you running, and what's the clearance now ?
typically Chrysler 50's specs are very tight, I've seen oil bearnig clearance listed at only .001" rods/mains, which is on the tight side-they obviously wanted the engines to run a long time before getting loose, and bearing technology back then, was not what it is today either
I could dig out the Mopar spec book but no matter what your out of round is, it depends on what pistons you're using and bore size too- a block bored without a torque plate goes out of round when you torque the heads down anyway, .002"-.003" or more, so what you see without a torque plate on the engine, changes when you torque down the heads- this is why a torque plate is important
regardless of what the specs say, you can go to .0035" piston/bore clearance in a worn engine, if you hone it and put new rings in they will take up the clearance- much beyond that and you'll get a piston slap with cast pistons- forgings are more forgiving and can expand more and take up clearance in the bore.
I have witnessed bullders go even further than that, who put rings on old pistons with .005" piston/bore clearance- the engine runs strong, doesn't burn oil, but has a faint "tonk-tonk-tonk" when cold, that never really goes away completely- one guy put rings on a Dodge engine that was .010" piston to bore, it ran good for about 10,000 miles, then started slinging oil all over the place from blowby
forgings are way more forgiving, I've seen another racer who would freshen his bracket motor every 2 years, just put new rings on the same forged pistons, and hone the cylinders again with a torque plate- eventually it was up to .013" piston/bore clearance and still ran in the 8's in the 1/4 mile, that was a 465 Pontiac with 13.8 CR in a tube chassis car that weighed 2200 lbs.- but that was a trailered car with a pan vac and vacuum pump, not a street car
what type of piston are you running, and what's the clearance now ?
typically Chrysler 50's specs are very tight, I've seen oil bearnig clearance listed at only .001" rods/mains, which is on the tight side-they obviously wanted the engines to run a long time before getting loose, and bearing technology back then, was not what it is today either
I could dig out the Mopar spec book but no matter what your out of round is, it depends on what pistons you're using and bore size too- a block bored without a torque plate goes out of round when you torque the heads down anyway, .002"-.003" or more, so what you see without a torque plate on the engine, changes when you torque down the heads- this is why a torque plate is important