Taper Honing

[John Haskell]

For the engine builders out there.

Is there any taper honing going on with these long stroke engines ?

The bottom portion of the bore is tighter by .002" if we could get it. This was used when we ran BRC pistons in Modified Production.

Then, .010" was normal out to .012" after several tune ups. BRC's were loud out there but grew really fast. The taper helped the bores & the piston but these didn't come out of the bottom bore like todays strokers.

You stayed out of the top ring travel as best you could. This process wasn't easy, very slow.

Just curious if you boys are using this method with these stroker engines which have so much of the piston out of the bore.

[Walter R. Malik]

For the engine builders out there.

Is there any taper honing going on with these long stroke engines ?

The bottom portion of the bore is tighter by .002" if we could get it. This was used when we ran BRC pistons in Modified Production.

Then, .010" was normal out to .012" after several tune ups. BRC's were loud out there but grew really fast. The taper helped the bores & the piston but these didn't come out of the bottom bore like todays strokers.

You stayed out of the top ring travel as best you could. This process wasn't easy, very slow.

Just curious if you boys are using this method with these stroker engines which have so much of the piston out of the bore.

I have heard of a thou smaller at the TOP because of combustion heat but, not small at the bottom.

I will and have always used straight and round with a deck plate on everything.

[PackardV8]

I will and have always used straight and round with a deck plate on everything.

You and me, Walter; that we can control and measure. Trying to guess where the cylinder and piston are going to be at full heat and power is for most of us just a WAG.

[SupStk]

True it is WAG but I do .001 small at top but it is a hold over from the 2 stroke dirt bike days. Those I did with .0005.

[engineguyBill]

I will and have always used straight and round with a deck plate on everything.

X3! I can see no benefit in trying (repeat TRYING) to purposely put a taper into the cylinder wall for any reason. There is no way that this taper could be consistently formulated and assigned to the cylinder wall architecture - in my opinion.

[MadBill]

I'm sure I read that some air-cooled aircraft engines bores are specced to be smaller at the top.

[modok]

The bottom half of the cylinder tapering larger is probably ok, or, the lesser evil.
I'd like the top half to be straight.

[stealth]

If there was any benefit to this I think the oem’s would have found it thrying to squeeze out any crevice volume in search of mileage and emissions gains.

[DCal]

For the engine builders out there.

Is there any taper honing going on with these long stroke engines ?

The bottom portion of the bore is tighter by .002" if we could get it. This was used when we ran BRC pistons in Modified Production.

Then, .010" was normal out to .012" after several tune ups. BRC's were loud out there but grew really fast. The taper helped the bores & the piston but these didn't come out of the bottom bore like todays strokers.

You stayed out of the top ring travel as best you could. This process wasn't easy, very slow.

Just curious if you boys are using this method with these stroker engines which have so much of the piston out of the bore.

John, yesterdays BRCs were a mess with the taper they used. I saw Bill Maropulos' block and the rings actually bored the block because the pistons rocked so much. Todays pistons with CAD help can make piston skirts that stabilize the piston in the bore with different cam and barrel shapes and the rings last more than they used to by a large margin.

[modok]

What is a BRC?

[norm]

A brand of pistons.

[Keith Morganstein]

What is a BRC?

BRC Performance, a custom piston company in FL, USA.

They will make just about anything,... if they have a blank in the size range. I’ve had them make some oddball stuff, but haven’t used them in maybe five years (been staying away from the one-off custom builds)

I think they are still in business, the website is up, (but some pages have issues)

http://www.brcperformance.com/about.html

[modok]

AHA!
thanks.

[John Haskell]

Now I'm trying to remember what the deal was in piston roc at BDC, vs. TDC, but it was a ton when the piston came out of the bore. .016 at the top cold depending on the skirt tail length & .030 at the bottom. (??).

Tightening up the bottom, reduced the roc just a bit with out fixing it, because you couldn't fix it.

When your watching & listening to the piece & what's being said, you learn something & do something about it. Its all about science & working it out to a conclusion.

Those days were tough compared to today & I really believe the real thinkers came from the late 60's through the mid 80"s & passed it on to all we have today.

Could it be that this is over looked even today ? If you don't see any chewing on the piston skirt & wall, you have no concern.

But, you might learn something if it fits what your doing in bore length. Seems to me that Dart must have thought into it due to the bore length increase built in.

[Walter R. Malik]

A piston which comes out of the bore a lot at bottom dead center SHOULD be addressed with the piston SKIRT; not the bore of the block.

A barrel shaped piston skirt with the largest diameter near the pin center-line is needed, not a long tapering skirt with the largest part .5" below the pin centerline.