1981 R65 Valve clearance spec?

[ShutterPilot]

Hi all,
I searched for this, honest, but not getting anywhere due to SO many returns on "valves" so I thought I'd consult the hive.
My OEM Owners Manual for my 81 R65 list the specs for the valve clearances as
Intake .05mm (.002in)
Exhaust .20mm (.008)

Haynes list them as .004 and .008 respectively, yet I've also seen where "all airheads" are listed as .1mm intake and .2mm exhaust.
Are the values between type 247 (most airheads) and type 248/1 engines on the R65 being conflated here?

I had been gapping .002 and .008, but that guage set got rusted and looking for new guage set. Just want them to be right.

What are post-81/Pre-monoshock owners gapping to?

[georgesgiralt]

Hi !
As far as I know, BMW changed specs many times about valve lash.
In 81 they gave .05 mm for intake but corrected it to .1 mm at some point.
I put 0.10 mm inlet and 0.20 mm exhaust as advised by the local BMW  Guru and the valves live well and not too noisy.

[Tony Smith]

Been using .10/.20 mm for 44 years.

Never lost a valve

Reminded of old advice "a rattley tappet is a happy tappet."
 

A friend and I were discussing our motorcycling experience in another context recently. I think I can lay claim to having been using those valve settings for about 800,000km.

[Barry]

When the 81 model was introduced the quoted power output for the R65  went up from 45hp to 50hp due to bigger valves.  One theory is they tightened the valve clearances up to squeeze the last bit of power out of the engine. The recommended 2 thou inlet clearance only lasted 1 year because it was increased to 4 thou by a service bulletin in Nov 81. The reason they gave was an increased safety margin. The recommended exhaust valve clearance was also 6 thou for a short time.

4 thou and 8 thou are now the universal recommendation.

The bottom line is the exact clearance is not that critical, it's more important that both cylinders are set as close as possible to be the same and it's more important to compare measurements between services to detect any signs of valve recession.

[Tony Smith]

Barry.

I think you give BMW too much credit.
I don't think that they spent months micro adjusting valve clearance, ignition timing, jetting etc in order to get 50hp from the post 1981 R65.

I think they just flat out lied!

[georgesgiralt]

Hi Lads,
IMHO, BMW specified a very tight valve clearance in order to reduce as much as possible the noise. At that time, everyone complained about it stating that those engines where more noisy than a cal 50 machine gun... It was the time Japanese bikes transitioned to double camshaft in the heads with valve clearance adjusted with thick disks and that was silent...
But by specifying such narrow clearance, they did not take into account sloppiness of the average mechanic. So some bikes came back with burnt valves with a warranty claim....
They dropped the towel on the noisy valves and studied other solutions to reduce the noise....

When I bought my R65, all my friends kept telling me they could hear me coming from miles because of the valve train noise.... (was not true, was the dead Zeuna muffler they heard.... )

[Barry]

I think they just flat out lied!

I think so too, especially about the lower compression US versions.

[dogshome]

My butt-dyno totally confirms not 50BHP. I shouldn't have had to panic when merging with lorries doing 60MPH from an on-ramp / slip road. My old 250 had about 35-40BHP and would lift the front wheel easily when on power-band and I never felt panic that I couldn't get up to speed fast enough. The 500 single (albeit with flat track cam, huge carb etc) also never felt inadequate. 100cc 2 stroke Suzuki single on the other hand did need lots of thinking and winding-up time. CG125 was totally inadequate for joining a major road. Sit and wait, or give up and go another way.

Hence the 860 upgrade.