Who has honed a bore oversize?

[bryanwess2000]

I just finished honing my L3 90hp and had to oversize the #2 cyl. +.020.
I only did this because no one close does blind bores. I kept the bore to
.0005 taper and .0005 egg but it took alot of work dressing the stones.
I used mineral oil to hone with since I bought the hone and stones used
and they had already been oiled. I used a goodson rigid hone which is a
copy of a sunnen an112.
I'm looking for pointers on oil to use, ways to dress the stones to keep
taper and barrel to a minimum. Plateau finish or not? Is it worth buying
trueing cylinders ? I plan on doing a few motors a year as a hobby and
was looking for some tips if any of you care to share. You can PM me
if you don't want your tips made public.

 

[4JawChuck]

Re: Who has honed a bore oversize?

Mix hydraulic oil 50/50 with varsol or kerosene for an excellent honing oil. Thin any oil mixture you use to the consistency of water. Really any oil works fine, its only for cooling anyway. The Varsol or kerosene is just to thin the oil and reduce surface tension so it removes heat faster.

Use coarse stones to remove material as quickly as possible, the longer it take to hone the bore the worse the egging and taper can get. The idea is to hone to size as quickly as possible to keep the original round straight bore as it comes off the boring bar. Cool the block frequently in kerosene or varsol to prevent heat building up and distorting the bores, the more tapered the bore the hotter it gets in the areas where the taper is since your removing more material there.

A good trick is to use cooled oil as your honing, one shop I worked at had a cold water heat exchanger for the oil since we did nothing but chrome bore aircraft cylinders which are really hard and need a lot of honing to size them. You could fabricate a similar contraption with a car heater core that you passed the oil through after pumping, immerse the heater core in a bucket of cold water and keep a hose flowing into the bucket. Make sure you filter the oil before pumping or your just recycling hone/bore particles which will scratch your fresh bores.

Really the only trick I can think off thats essential is to make sure the bores are cold prior to plateuing the finish and final sizing, not such a big deal on cast iron but on AL blocks its very important.

 

[bryanwess2000]

Re: Who has honed a bore oversize?

Do you have any problems with the kerosene breaking down the stones
faster. Is there a formula for the desired crosshatch based on rpm, stroke
length and diameter that determines strokes/min. ?

I used a set of 70grit stones to remove all but .002 and it came out pretty
fast but started tapering so I had to dress the stones several times to correct
the taper. I read some people use the coarse stones dry, I would think that
would generate alot of heat and you'd have to leave more stock to finish
since the surface finish would be scratched deeper from not using an oil.
Anybody else have experience with this?