1948 ul

[Joe G]

Hello Everyone, last week I worked out a deal for this 1948 UL. Some of you may have seen the bike as I think it has been traded around the circuit for some years. When I started it up it had a horrible top end noise so I pulled it down to check it out

[Joe G]

IMG_0383.jpeg IMG_0384.jpeg

The oil light didn't work so my initial thought was the bike had been sitting a long time and someone fired it up with little or no oil. When I got the heads off, I could see the pistons were .020 over and they had significant wiggle back in forth in the bores (piston slap). Then I wondered if the bore job was horribly off. Tonight, I pulled off the front cylinder to find a badly scored piston, no cylinder wear, and what appears to be a very clean motor inside. The pistons do not have a maker's name and do not have the steel inner rib. I checked the piston the best I could with some dial calipers and the size was a wopping 3.434 inches. Perhaps the pistons are .020 ULH pistons? I found a table in the Victory library that lists a Std. repo ++ size as 3.4375. Any thoughts on the best path forward? Thanks, Joe

Edit. The bore looks closer to 3.450 and these are 11 fin cylinders

[Jerry Wieland]

11 fin cylinders originally had a 3 5/16 inch bore = 3.3125" so your cylinders are .145 overbored. I have seen those cylinders bored into this range a few times. I do think that the big bore was the problem. Either fit was wrong or lack of oil. I prefer OEM pistons to any aftermarket stuff. Jerry

[Joe G]

Still doing discovery work. Here is the inner primary. Ugh, I don’t like belts.

[T. Cotten]

11 fin cylinders originally had a 3 5/16 inch bore = 3.3125" so your cylinders are .145 overbored. I have seen those cylinders bored into this range a few times. I do think that the big bore was the problem. Either fit was wrong or lack of oil. I prefer OEM pistons to any aftermarket stuff. Jerry

In agreement with Jerry,

Huge overbores on U series can instantly be an issue if not properly performed.

A stress-plate on the deck flange is mandatory, as a poke-and-hope overbore without one can result, when installed, in a distortion of nearly three thou inward AND outward of the bottom portion, especially at the spigot, thus chewing the piston skirts. This is where all the horror stories of excessive heat and fragged cylinders originate.

I can't find my scans of Essentials for Speed that illustrate the fixture, but it is the solution.

....Cotten

[Joe G]

Oddly the cylinders look nearly perfect. I would definitely like to find a set of UL or ULH cylinders but they seem to be horribly expensive and scarce.

[T. Cotten]

Oddly the cylinders look nearly perfect...

'Look', Joe?

No human eye can measure it in real life, much less a poor pic on a monitor.

Is the top two thirds of the ring wear- polished, and the bottom third still cross-hatched? Is there any of the deeper plateau cross-hatch still evident in the polished portion?

Do you have an accurate boregauge?

....Cotten
PS: I advocate properly-fit huge overbore cylinders instead of sleeving for many, many reasons,

[Joe G]

I meant that there is no scoring or burn marks. The cylinder does have a few thousandths wear in the piston travel area. Since these UL cylinders were already bored .020 over ULH size of 3-7/16, I would have to bore to 3.46+. I’m not going to take the risk of a cylinder breaking above the base so I’ll look for a new set of cylinders. Perhaps aftermarket even .

[T. Cotten]

I meant that there is no scoring or burn marks. The cylinder does have a few thousandths wear in the piston travel area. Since these UL cylinders were already bored .020 over ULH size of 3-7/16, I would have to bore to 3.46+. I’m not going to take the risk of a cylinder breaking above the base so I’ll look for a new set of cylinders. Perhaps aftermarket even .

Virtually every fragged cylinder, Joe,

Was either sleeved poorly, or fitted for the piston without a proper stress-plate installed.

A stress-plated cylinder is pre-distorted as if installed, thus the honed bore will return to 'round' after the plate is removed (upon which gross distortion will be evident) and then installed to the same torque spec.

Stress-plates have been the standard of the auto industry for many decades, but its beyond most modern harley builder's comprehension.

First, please measure the remaining wall of your cylinder bores, at the thinnest spots over each deck stud hole:
THINBORE.jpg

(Indian cylinder shown; Your U cylinders have huge spigots to get around, of course, but it is the huge spigots that transfer the fastener stress to distort themselves and the bore.)

....Cotten

[exeric]

Love the thumb screw on your calipers, Tom.