R80/7 1978 Correct Valve Clearance

[jackonz]

Am hoping someone will have the correct answer here, am re assembling the top end on my 1978 R80/7, I have the Clymer manual as well as a BMW factory manual. in both manuals it has the same settings for the intake valves but diffrent settings for the exhaust.

Am hoping that outthere someone has the correct setting for the exhaust.

[Kurt in S.A.]

I would recommend 0.15mm for intake and 0.20mm for exhaust. If you're doing a fresh topend/rebuild, then you might want to open up the exhaust slightly, then come back when things are done breaking in. The intake side gets "cooled" by the inrush of fuel/air.

Note that BMW did move around the values over the years. I think they initially were 0.10/0.15mm in/ex early on but the prudent settings are what I recommended at the top.

Kurt in S.A.

[barryh]

BMW issued service bulletins in 81 and 82 to increase the exhaust valve clearances to 0.2mm. Although the reason wasn't specified it was almost certainly due to concerns about clearances closing up faster due to unleaded fuel.

[Kurt in S.A.]

I'm also certain that was the reason. Of course, the issue in '81/82 were due to the poor choice of valve seat material which resulted in poor heat transfer to the head. It's hard to believe, that that small amount means that valve face will sit on the seat just a bit longer helping with cooling.

Bulletin 2096 in March 1984 suggests 0.15mm/0.25mm for the first 600 miles, then going back to 0.10mm/0.20mm afterwards.

Even if it's a pre 1981 engine, there's no significant downside to using the 0.20mm setting.

Kurt in S.A.

[barryh]

It's hard to believe, that that small amount means that valve face will sit on the seat just a bit longer helping with cooling.
Kurt in S.A.

I once did the sums on that and calculated how much longer the valve was on the seat and it's negligible. They opened up the clearance just to ensure that the clearances didn't close up before the next service. You have to smile at the wording in the service bulletin. For accidently changed read we accidently chose the wrong valve seat material


....this will greatly reduce the risk of engines being run with clearances that are too small if the settings have accidently changed