Tappered bore hone for heat tolerance

Having to learn to make best guess on Ms Peel bore to piston clearance before carbide impregnating. Frank Foster is a long time mentor to me and bunch of others and flashed back with his hard earned gemstone. So how might this translate on a spun cast iron sleeved 920 with JSM forged pistons hot rod? >>>>>>>>>>>>>>>

Frank learned a lot on his BSA B50 [a google example image]



Steve,

I've run that bike (10-1 CR, measured) on 87 octane for the last 20 years. One prior pre-ign piston failure, lotsa detonation without damage,
numerous skirt seizures.
I found that the bottom half of the cylinder stays small as the top half expands with heat. Seizures all at the bottom of the stroke. Cured it by taper honing .003" bigger at the bottom.
Who wooda guessed?

Dammit Steve!!! THREE GRAND taper is a TON! :shock:

concours said:

Dammit Steve!!! THREE GRAND taper is a TON! :shock:

Click to expand...

Yeah, I gotta agree; that's a bit large, although I've seen .001" spec'd out in some older air-cooled engines.
If you figure on how much you start with, then add to that an additional three thou, that leaves a pretty sloppy piston. I'd rather look for ways to keep the detonation at bay and the oil temp down.

Ok I needed some feedback on the sense of scale and excess .003" is. I want to make and sustain like 3x's the heat flow of a factory Combat w/o slapping pistons and bores silly or as much long stroke friction stifling the benefits of 8000 red line. Octane will not be Peels limiting factor. Fuel/air mix and heat distortion will be. If I knew how bores and pistons distort I'd have them alerted to fit better hotter but alas I don't so here I am scratching at straws before pulling trigger on another final commitment set in carbide. Narrowed down guestimate of piston clearance to almost coin toss decision. 0.0050" or 0.0055". Peel must be hobot proof so some slapping around may occur.

The Bore store said the land speeder supercharged 350 Honda had .0025" clearance but of course a shorter stroke smaller pistons so a shorter bore with more even heating zone with less expansion differences - but groin tightening for me to consider. I'm getting a bore guage so will monitor what the wear might tell me for next time around.

I remember my boss's RC plane engine with smaller than little finger bore had .0005" taper. No ring, lots of castor. Piston fit easily from bottom but barely came out top when cold.

I never asked but imagined Bore Tecs process uses a modified roller burnisher that doesn't release when stroke is reversed to impregnate the carbide into the bore. They can then stroke back an forth at low pressure for a long time. My experience with roller burnishers is a 3" bore in thick wall steel or aluminum bronze can be burnished .001"-.0015" larger with a 7 to 10 HP machine. I would group parts in lots within .0005" and adjust burnisher for different size lots. Burnished finish wouldn't come out right in a part with .001" taper.

My best guess is call and ask how much taper their machine can deal with. Maybe its spring loaded and can follow taper. Then I'd taper the bore .0015", .006" clearance bottom and .0045" top. You'll get good impregnation at top where it matters. I like the idea and hope it works.

[urlhttp://www.elliott-tool.com/id-roller-burnishing-tools/][/url]

Alrgithy edgefinder thanks for the educational engine insights to follow up on. Your tappered bore values really feel right to me. I'll call Bore Tech and quiz em on this option and how they impregnate bores. Past Peel had essentially whole engine dry firction Tungsten Dioxide nano particle coated but they did this by air pressure spray no contact tools involved. I did some years with the string controlled airplanes, which my dad gave me for X-mass but I had to wait a few weeks as he could not resist trying it out first and crashed it, so took a while for stores to restock. I was kind of upset having to wait but my opinion of my father's nature I inherited went way up.

Ya tagged the url instead of image brackets

That roller/burnisher is pretty cool, but can you follow it with stones to get the correct surface finish without removing the benefits of the now work-hardened surface? That looks more like something you'd use for a bearing surface rather than piston ring mating.