Big Bore question

[T. Cotten]

Back to topic, Folks,

Really advanced timing on one cylinder can burn it up, but most Shovels were not single-fire, so both cylinders had to be advanced; Why does only one burn?

Probably not the timing, huh.

....Cotten

[T. Cotten]

Thanks, Tom. Your comments on proper set-up and torque plate use makes a lot of sense. The big problem is finding shops that can, will, and know how to do that kind of work are quite scarce.

If you can fab the plates, Eric,...

Any auto machine shop should be able to handle it, as stress-plating has been state o' the art since the early Eighties, at least.

Since I couldn't bore for sleeving, I sent my Indian plates to the shop with the sleeves, cylinders, etc.

The machinist was amazed at the distortion of a cylinder-within-a-cylinder, and that was a Chief with tiny spigots.

....Cotten
PS: I cut plates for Knucks, Pans, Pans big-bore, Shovels, Shovels big-bore, and probably evos too.
None of them have been used for years.

PPS: Just for clarity, flattys don't benefit from the top plate like an OHV.
chfpla~1.jpg

[exeric]

Thanks, Tom. Your comments on proper set-up and torque plate use makes a lot of sense. The big problem is finding shops that can, will, and know how to do that kind of work are quite scarce.

[T. Cotten]

Do .070"-.080" over-bores in stock cylinders mean trouble, and unreliability?

Not if properly machined, Eric!

Torque-plate hone-and-fit anything sixty over or more. HD spigots distort wildly, and un-stressed bore jobs will rub the pistons, leading to all kinds of folklore.

torqplat.jpg

...Cotten

[exeric]

Do .070"-.080" over-bores in stock cylinders mean trouble, and unreliability? I'm probably looking at something like this for a Panhead motor. I'm not a motor guy, and not looking for horsepower; just wanting to use a nice set of correct year cylinders without going to sleeves. Thanks

[T. Cotten]

Torque, to much, to little... .

If it was just sloppy assembly, Duke,

Why wouldn't both gaskets blow?

Where did the heat come from?

....Cotten

[dukekleman]

Torque, to much, to little...
The items I've listed above are all relative to pressure being applied to the gasket surface sealing area. When analyzing, the end result is lack of sealing pressure. Even when over torqued, say like the inserts pulling, it still dismisses the sealing pressure applied and causes the failure.
Proper material, key word proper or correct, used in making a quality head gasket can with stand the temperatures themselves. They need correct torque for clamping force to seal and allow dissipation of the heat. If they aren't torqued correctly, the flame front and combustion pressure may be able to work away at the gasket. Dissipation of that heat is lost without the correct surface area contact and a failure occurs, loss of torque was the initial cause...
All the items I've listed above can cause the improper torque clamping value.

[T. Cotten]

I honestly can't say I've run into a shovelhead, head gasket failure, I'd blame on heat alone. Granted our climate up here is cooler so our oil temperatures don't always reach their optimal temperature.
Heat is an engines friend until in excess and becomes the enemy...Your right, it must be monitored and controlled for sure!

Please Duke,

If not heat alone, what did you blame it on?

Heat is always the common denominator, and gaskets don't see much friction.

Combustion is where the heat comes from, and when one cylinder exceeds the other, something lit the fuse.

....Cotten

[Jerry Wieland]

Some big bore ZEL rear cylinders also have a problem with the head bolt nearest the exhaust port. The casting is incomplete under the top fin and causes distortion which causes blown head gaskets.

Jerry

[duffeycycles]

I've had a few come in with both head gaskets blown.A student bought a cool FX with FL fenders cheap.Rode to iowa city on freeway,each hill was worse only 45mph at the top of the hills. As dukekleman mentioned overtorqued head cause the inserts in the cylinders to pull up causing uneven surface.This is the most common issue I have seen.

[dukekleman]

No , I can't say I've seen that one. Literally blown together? I would assume something very major, cylinder head to cylinder fitment /clearance issues or defective fasteners.
I have seen defective cylinder head bolts break, while the engine was on the bench in the engine stand. Next morning broken head bolts were laying on the bench top from both cylinder heads. There was a service bulletin on these after market fasteners due to manufacturing issues.

[T. Cotten]

I honestly can't say I've run into a shovelhead, head gasket failure, I'd blame on heat alone. Granted our climate up here is cooler so our oil temperatures don't always reach their optimal temperature.
Heat is an engines friend until in excess and becomes the enemy...Your right, it must be monitored and controlled for sure!

Ever see both head gaskets blow at once, Duke?

Anybody?

When one head gets much hotter than the other, it ain't climate change.

....Cotten

[dukekleman]

I honestly can't say I've run into a shovelhead, head gasket failure, I'd blame on heat alone. Granted our climate up here is cooler so our oil temperatures don't always reach their optimal temperature.
Heat is an engines friend until in excess and becomes the enemy...Your right, it must be monitored and controlled for sure!

[T. Cotten]

You forgot the prime cause, Duke!

HEAT

.....Cotten

[dukekleman]

I agree Cotton, they don't...areas of concentration when dealing with a blown head gasket vary based on engine design. In the case of a shovelhead engine, I've found over the years a standard list of checks...
1) Head bolt integrity/quality
2) Proper head fastener torque value, sequence and re-torque. MLS gaskets having a different sequence than conventional gaskets
3) Cylinder head bolt insert failure or inserts that are proud to the surface
4) Cylinder head gasket surface trueness
5) Cylinder heads and/or Cylinders that have been resurfaced to excessive and require different length head bolts
6) Cylinder head and Cylinder RA surface finish.
60 RA for conventional gaskets and 30 RA for MLS gaskets
7) Fire ring interference due to machine work and various head gasket thickness
If the above items are correct, accounted for and performed no issues should arise...