37 ULH tolerances

[Kansasplowboy]

Just aquired a 37 ULH and need some advice on the bottom end. Does the rod sideplay at TDC tell the whole story about the condition of the rod brgs? The forked rod is really tight, the single rod at the top of the wrist pin hole measures .082 side to side. If I read right, maximum allowable is 3/32 or .09375, that being said, would it be advisable to rebuild the crank? End play without the gearcase cover removed (don't have the lifter blocks pulled yet) measures .006 but wondered if that can be entirely accurate with the gearcase still on. This appears to be a very unmolested engine, been bored .020 but has unmatched pistons installed. Both exhaust valves were stuck open after being in a woodshed for 28 years after the bike was wrecked. One head has a hairline crack from the outer radius of the bolt hole to the edge of the head. Doesn't appear to have ever leaked looking at the gasket. The engine didn't have the correct carb. It has a M-51 and needs a M-51L if I read right.
Any input you guys have would be appreciated on what are quality replacement parts and what to stay away from.

Thanks,
Randy
AMCA#19727

[oldsouthmcy]

If this were my motor, I would take it all the way down and inspect all of the pieces.

Your motor has been in a woodshed for 28 years, the rolling parts have not moved in that time. Depending on the oils left in the motor at that time, you may have rusting and pitting where the metals have been in constant contact with each other for that 28 years.

However, before you do this, test the rotation of the flywheels before the gear cover is removed. The resistance should be minimal. Remove the gear cover and again test the rotation, there should be no resistance. Either test will help identify problems.

After disassembly, check all the rollers and roller surfaces condition. If all is well, you can reassemble the lower end with all the original parts and all you are out is the cost of a flywheel truing bill. Be sure not to mix the rollers.

While you are at it check the cam lobes and bushing fit. Check the valve springs for strength, especially those left open.

What can happen if you do not split the cases? Besides lack of piece of mind, if the corrosion at the bearing surfaces is severe, the case hardness might be penetrated. If the hardness is penetrated, the hardened surface of either a race or shaft can break loose. And if that happens, you will have to replace every shaft and race, including rod races, and bearing. The hardened surface material will spread in the oil and embed itself in all moving surfaces making it possible for the motor to fail pre-maturely after the rebuild.

I use Jim's and Eastern's mechanical parts for the bottom end.

[Kansasplowboy]

Thanks oldsouthmcy, I'm in the process of doing just what you suggested, a complete tear down. Pulled the lifters and can see the rollers need replacing for sure (pits), getting ready to pull the gearcase cover. As to the resistance of the flywheels, it rolls really smooth so I'm hoping it looks good when I pull it apart. I'm using Bruce Palmers book as a guide but also looking for advice from guys who have travelled this road before. Been through many auto and aircraft engines but this is my first journey into the deep dark bowels of a Harley bottom end.
Thanks again for the response.
Randy

[Sargehere]

i have a ULH front cylinder that has a hairline crack from the outer edge of the front-motor mount bolt hole, through three fins (on top of the intake manifold where the boss stops in mid-air). It prevents torquing down that head bolt, as the hole just begins to expand. In service, that bolt worked itself loose repeatedly, blowing head gaskets at that point. Once I figured it out, I simply drilled safety-wired that head bolt to the top motor mount, and it's been perfect ever (decades) since, welding not required.

The old Flatheads are tough motors, but they do need clean, close tolerances, but remember that they're not exotic just because they're Harley. It's just big air-cooled internal combustion engines. Like a really big Briggs & Stratton lawnmower engine, really.