80" Shovelhead Cylinder Discrepancy?

[gitguy]

I acquired 2 sets of 80" shovelhead cylinders. They have identical casting numbers. However, one set has the correct stock factory bore of 3.498" but the other one is 3.436 which is standard for a 74" motor. They both appear to have never been installed - no visible wear on the cylinder walls. Looking closely I can still see some of the cross hatching. For sure they've been sitting around unprotected hence the surface rust.

Any thoughts on this 74" cylinder bore on an 80 incher?


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[PanheadFred1]

You might have trouble finding pistons for the 74" bore and the 80" stroke.

[duffeycycles]

1978 had both 74 & then the 80 came out,maybe that is when these were made?
On my wall is the original dealer flags for 75th anniversary models

[joe fxs fxr]

That's why it's impossible to tell a 74" motor from an 80" from the outside.

[jim d]

As I recall they were the same cylinder for the 74 and 80 inch motor when the 80 inch motor was introduced. You just didn’t have as much left to bore oversized. So they bored them for a 80 inch motor and charged you more for the bragging rights. I had a 82 FLH Classic 80 inch that had a piston slap at 4K bored it .010 over and the crank cut loose at 7K sounded like a big hammer in the cases. I bought 74 in cylinders from the late 70s same numbers and put a small stroker in it. It was also equipped from the factory with a sidecar. I sold it 10 years later and the new owner wanted to freshen up the top end. They called me because they couldn’t figure out what pistons to buy for it.

[Jerry Wieland]

A friend of mine ordered an 80" FLH and the first time he went to have it overhauled it turned out to be 74". The dealership traded him a brand new FLH for his old one. Even had the 80 fender tips.

[gitguy]

This was all helpful. Learn something new all of the time.

[duffeycycles]

I rebuilt a 1978 74" FLH OP that had the 75th anniv decals/emblems

[gitguy]

I rebuilt a 1978 74" FLH OP that had the 75th anniv decals/emblems

It had the thick base and 80" cylinder casting numbers?

[duffeycycles]

I think it did,that was several years ago

[Underdoggie]

As I recall they were the same cylinder for the 74 and 80 inch motor when the 80 inch motor was introduced. You just didn’t have as much left to bore oversized. So they bored them for a 80 inch motor and charged you more for the bragging rights. I had a 82 FLH Classic 80 inch that had a piston slap at 4K bored it .010 over and the crank cut loose at 7K sounded like a big hammer in the cases. I bought 74 in cylinders from the late 70s same numbers and put a small stroker in it. It was also equipped from the factory with a sidecar. I sold it 10 years later and the new owner wanted to freshen up the top end. They called me because they couldn’t figure out what pistons to buy for it.

I had a real early 78 1/2 80 inch tan and creme classic, it would go thru a quart of oil about every 4 or 5 hundred miles but had great compression, when I finally tore it down I saw what you were talking about with the same cylinder, the head gaskets were washed out all around the that oil return hole from the rocker boxes because it was so close the the cylinder lip. It was sucking the oil right out the exhaust. I was told the later ones were a different casting and they moved that hole in the cylinder and jug out a little to stop that problem. I used to carry a few extra cans of oil and zero my trip meter, when it got to 400 i would just put a quart in. Strong runner tho.