Big Bore question

[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

[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]

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]

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]

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

[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

[dukekleman]

One can only make an assumption in this case and my assumption/experience has seen improper torque and re-torque on the rear cylinder, left side rear head bolt to be one of the most common. The clutch cable minor adjuster gets in the way. People use dog bone adaptors that contact the cable adjuster falsifying torque value. I've seen many technicians do this when mentoring them.
Assuming points are being used in this situation, a technician must be aware of the advance weight pedestal fitment. Depending on the camshaft manufacturer and the advance assembly manufacturer, I've seen the point gap vary dramatically front the front cylinder lobe to the rear cylinder lobe. Sometimes a light tap on the shaft can true things up nicely for equal gap settings. This causes obvious timing issues...

[T. Cotten]

One can only make an assumption in this case and my assumption/experience has seen improper torque and re-torque on the rear cylinder, left side rear head bolt to be one of the most common. The clutch cable minor adjuster gets in the way. People use dog bone adaptors that contact the cable adjuster falsifying torque value. I've seen many technicians do this when mentoring them.
Assuming points are being used in this situation, a technician must be aware of the advance weight pedestal fitment. Depending on the camshaft manufacturer and the advance assembly manufacturer, I've seen the point gap vary dramatically front the front cylinder lobe to the rear cylinder lobe. Sometimes a light tap on the shaft can true things up nicely for equal gap settings. This causes obvious timing issues...

The whole torque technique, Duke,

Will always demand prep, proper wrenches, and observation, etc. But there's been far too many burnt gaskets that weren't by the clutch adjustor (even if the model had one).

They always run for a while, sometimes a long time. Then temps spike, for some reason.

Points gap issues are not just a Shovel concern of course, and certainly affect performance. But causing one head to burn and not the other would take a pretty wonky assembly!

Burnt gaskets have always plagued internal combustion engines, and the most common cause has always been there too.

....Cotten
PS: Anybody remember when the early '80s models started dropping valve seats? That took a lot of heat, yet the gaskets survived.

[PaulCDF]

Not to hijack OWGs thread (He said as he hijacked the thread).
Eric brings up a point "a nice set of correct year cylinders without going to sleeves"
Is there something inherently weak with sleeved cylinders? Or is it the craftsmanship or lack there of that goes into the sleeving?
Not looking to be contentious, just trying to learn. As original parts for antique bikes become ever scarcer.
Is it a "judging thing" not to use good reproduction cylinders?

[exeric]

I've had an Indian, and a Harley with sleeved cylinders and no problems. I do wonder if how a motorcycle is used can cause problems assuming the motor was well built. In other words, if a bike is ridden long distances and continuous hours, or just used around town, and short pleasure rides. I'll bet there is a lot of good data from Cannonball engine builders but that seem to be closely guarded stuff. Here at the AMCA forum we rely on freely given info from Cotten, Dukekleman, Robbie, and others with real world experience; which I thank them for.

[T. Cotten]

Not to hijack OWGs thread (He said as he hijacked the thread).
Eric brings up a point "a nice set of correct year cylinders without going to sleeves"
Is there something inherently weak with sleeved cylinders? Or is it the craftsmanship or lack there of that goes into the sleeving?
Not looking to be contentious, just trying to learn. As original parts for antique bikes become ever scarcer.
Is it a "judging thing" not to use good reproduction cylinders?

Repop cylinders can be quite a problem, Paul!

Not that there may be quality now available, but its a still a choice between originality (plus getting your money's worth out of what you got...), and compromises cast into the repops. (I have an oriental pan cylinder that had been bored to paper-thin at thirty over, and ran fine until it tossed a wristpin clip. Then I put my fingernail through it:

PERFDCYL.jpg

Sleeving can be performed correctly of course, but I seriously consider a larger overbore much safer and cheaper, if performed correctly. Sleeving involves more procedures, and as this Chief sleeve shows, a careless installation spells disaster: Sleeves insulate even when perfect, but a toolmark can guarantee a melt-down..

SLEVBURN.jpg
(Outside of removed Chief sleeve.)

We can get into techniques, but everything depends upon what you have to work with.


....Cotten
PS: Late edit, Folks,
I found a pic of the cylinder bore for the burnt sleeve; You can see the horrendous tool-chatter contributing to the melt-down.

CHATTER.jpg

[PaulCDF]

Thanks Cotten;
All comes down to resources and finding a good craftsman you can trust.

[T. Cotten]

Thanks Cotten;
All comes down to resources and finding a good craftsman you can trust.

As I posted, Paul,

Any competent auto machinist should be capable, if you arm him with some specialized tooling, and most important, information. Finding an experienced hand who doesn't think he knows better can be a problem.

Most auto shops who install sleeves deal only with water-cooled motors, where heat transfer isn't life-or-death.
For an air-cooled motor, the thou and a half interference for a sleeve doesn't encourage heat transfer, so the finish to accept the sleeve must be as micro-fine as possible; Even a plateau finish only conducts at the plateaus. ("Seal-Lock" fills the rest of the voids.)
Graciously, the LA sleeves I used were almost reflective (but that was more than a few years back.)

Boring for a sleeve blows out the casting much farther than the largest overbore, so I prefer the overbore.

...Cotten
PS: Here's what over-zealous sleeving
can do:

Perfdcyl Indian.jpg

perfdcyl 3.jpg
Dixie had Pan/Shovel pistons up to a hundred over. I fit a set, but I bet the fellow still has them on the shelf: He's a collector.

[dukekleman]

I agree, I've bored a number of Panheads over the years at .080". All of them I'll call local bikes because I run across them time to time. Out of all of them I've done, the last one is has been over 25 years ago, they all still run fine without issue. I could ramble on about what has built my confidence in using .080" pistons, because at first I was skeptical. I'll just share that I've been with a couple of these Panheads bored .080" on trips that have covered multiple states, various climates and elevation change, they survived just fine.
RA finish is very important and should not be overlooked. RVK and RPK are considered when machining any surface for particular applications. There are multiple numbers used in each application if you will. Wheel hubs, brake drums, connecting rods, pinion/sprocket shaft races, valve guides, gasket surfaces, cylinder walls and exactly what Cotton said, sleeving. I've seen sleeve jobs that act as an insulator of heat transfer like the images shown above. A very fine RA finish along with X and Y measurements within 0.0002" is required between your interference surfaces when sleeving. I prefer to resurface the base gasket and head gasket areas to not only get the correct finish for the gasket of the era being used but also to insure things are square if you will... I've seen a few shops around my area skip this important step.

[exeric]

Thanks to Tom, and Duke for their patience, and indulging my remedial motor questing. Also my apologies to OWG for leading things off topic.