head questions

[mack]

Been working on Sica's head for the last couple days and have a couple questions. First, are the oil return gallery's larger at the exhaust side because the motor is tilted in that direction and the cam lobs throw in that direction?
Second pertains to the bearing surfaces under the caps. The PO didn't believe in changing oil or filters I guess. The bearing surfaces, (and the cams) are all surated with grooves. Looks like metal filings were drawn up into the cams from the sump. I'm not too happy about this as the bike has less than 10 k on it. That's why I bought it. At least the grooves are all in line with the rotation. How much is too much. Also as a side issue. The last guy to shim this went the wrong way with #3 & #4 exhausts. Not sure how many miles were put on with it hammering like that, but I'd say a fair amount. A quick check indicates those two need to be upped to 305 when the other two are 285. My question is can the valve seats be replaced?

[TopCatGr58]

Hey Mack,

If you've got prominent grooves dug/cut into the cam bearing surfaces, then you may be in need of a whole new head. The bearing surfaces need to be fairly flat/smooth to create that thin layer of lubricating oil/film between the two parts. Grooves allow the oil to flow in the grooves and can prevent as much getting across the whole bearing surface, which leads to more friction, wear, etc.!

Disclaimer, I'm not a real pro-trained MECH, so other real mechs may chime in here with more precise info about this! The valve seats tend to get hammered into the head anyways, that's why the clearances shrink with wear instead of getting wider. As long as you can get the required shim size and valve clearance, and a good valve/seat seal, you shouldn't need to worry about replacing the seats, but I don't recall seeing them on any parts fiche...just the valve GUIDES and seals and such!

T.C.

[crazy steve]

One reason the oil galleys may be bigger is to carry away more heat; the oil does double-duty in air cooled motors.

Cam/journal wear? Well, any sort of grooves worn in either the bearing surface or cam journals isn't good, but check clearance with some plastiguage to see where it's at. If it's still within spec, I'd at least try to run it. Worn too far, you're probably looking for a new head. As to the valve seats, same thing. Unless you've got loose/excessively worn/damaged seats, I wouldn't worry too much. Any competent machine shop should be able to replace the seats, as you only have to roughly match the valve size for a replacement seat.

[mack]

Thanx

I'll check it with the plastique but when I was hand polishing the surfaces they didn't look to good to me. A while ago there was someone who broke off a spark plug and couldn't get it out of the head. Someone else posted a thread about a guy in Chula Vista who had several heads. Graigs List I think.I can't find it. Anyone in that area know if one of them is from an 81 LH?