1979 CB750k - Valve Clearance Clarification

[Piczker08]

Hey All,

Was curious to see, at what point is a valve clearance too loose? I've heard plenty that loose it better then tight, but curious to see what is too loose.

I'm working on setting my valves and, with my current collection of shims, ive got 3 that are sitting at 0.007 and one that sits at 0.008. The rest sit at 0.005 and 0.006.

Do we see those as too loose? Would i see some compression loss with those few sitting so loose?

Thanks

 

[dirtdigger]

I would consider those too loose. .007 is on the edge but .008 is def too loose. .005 is ideal. Loose will beat up the valve train, tight will burn the valves. It is odd to see them loose unless the cam lobes are worn or cam bearing clearance is loose. 99% of the time clearances get tight on these.

 

[Piczker08]

Mostly that loose after adjustment using the combo of shims i had to bump the clearances up a bit, that's what i ended up with. I haven't run the motor yet but i did check cold compression (carbs off so no throttle) as part of my winter work and im getting pretty low compression on the cylinders. Like 120,60,30,40. Can it be related to loose valves? Oil in cylinders doesn't improve numbers.

 

[kirky]

it could be bad seating of the valves or ring/ piston /bore wear, i think it has been mentioned on here that at 30,000 miles they are ready for a valve job, mine is on about 30,000 and just manages about 100 to 125 psi across the cylinders . it doesn't like starting easily in the winter and the carbs have been sorted, it's fine in warmer weather but i park it up in winter.

 

[Piczker08]

Hmm yeah this ones got about 18.5k miles. But had a refresh at 17.5k with new redone bottom end. Aside from new cam bearings and valve stem seals no other work to the heads though.

I had a day this fall where the engine flooded with fuel due to bad float needle. Ran for about 30sec before I caught on. Doubt it scored the walls that quick at idle but I wonder if it loosened up some deposits that gunked up the seats?

 

[Bo82CB]

Adjust all the valves to to .005, buy / borrow different (good working) compression gauge and do the test, go from there.

 

[chuckt52]

I have been told (I think by amc49) to go higher on the valve clearances. Spec is too tight. Anyways I shot for .08mm all around with a range of +.05 and -.02, so anywhere between .13 and .06.

 

[BAHNST]

Are some quoting mm?

 

[Old_Crow]

Are some quoting mm?

The factory specs are in mm, I believe that the commonly quoted .005 that everybody uses now is in inches.

 

[chuckt52]

Are some quoting mm?

I didn't catch that. Makes sense. .005" = .127mm

 

[Twobond]

I would consider those too loose. .007 is on the edge but .008 is def too loose. .005 is ideal. Loose will beat up the valve train, tight will burn the valves. It is odd to see them loose unless the cam lobes are worn or cam bearing clearance is loose. 99% of the time clearances get tight on these.

 

[Twobond]

hello bikers
Attached is my valve clearance
Which ones needs adjustment
Walter

Hey All,

Was curious to see, at what point is a valve clearance too loose? I've heard plenty that loose it better then tight, but curious to see what is too loose.

I'm working on setting my valves and, with my current collection of shims, ive got 3 that are sitting at 0.007 and one that sits at 0.008. The rest sit at 0.005 and 0.006.

Do we see those as too loose? Would i see some compression loss with those few sitting so loose?

Thanks

 

[chuckt52]

They all look tight to me. Again, I go with .08-.13mm. I start on the loose side cause they will tighten up over time.

 

[Twobond]

Dear 750 people,

I am trying to adjust my values on my 79 750k.
My valve is at .007. My shim on that valve .295 mm. Would I place a higher shim (.305) or a lower shim (.285) to get the valve to .005?

Walter Houston

 

[chuckt52]

Dear 750 people,

I am trying to adjust my values on my 79 750k.
My valve is at .007. My shim on that valve .295 mm. Would I place a higher shim (.305) or a lower shim (.285) to get the valve to .005?

Walter Houston

Smaller shim will give you more gap. Larger shim will leave less gap. (The valve is at rest, the cam is at rest, the difference in gap is how much stuff you have inbetween those 2.) Example would be a water bottle. Its 20oz no matter what. There can only be air and liquid. The more liquid (shim) the less room there can be for air (gap)

 

[bbaart]

Dear 750 people,

I am trying to adjust my values on my 79 750k.
My valve is at .007. My shim on that valve .295 mm. Would I place a higher shim (.305) or a lower shim (.285) to get the valve to .005?

Walter Houston

Looks like your mixing inches and millimeters. Use a metric leaf feeler gauge as the shims are metric as well. Much easier. Using metric the spec clearances are 0.08mm +0.05mm -0.02 mm. For example if your clearance is 0.18 and your shim is a 295, then you want a 305 shim to get the clearance down to 0.08.
Note fyi: I have always tried for larger clearances on the exhaust (0.10-0.13) and smaller on the intake (0.06-0.08). This engine has been known to burn exhaust valves so a larger clearance keeps the exhaust valves slightly cooler. A larger clearance causes the valve to seat in the head longer and it is when the valve is seated in the head that it cools off. You can get away with a smaller clearance on the intake as cool fuel/air runs past the intake valves so they are always cooler. Plus you get the added benefit of increased performance.

 

[Twobond]

Thank you, for your information. I will get the valve and timing chain just perfect on my ‘79 750K with wind jammer
Walter Houston

 

[Twobond]

One more thing, when adjusting the valves should the timing mark be on the “T” for top dead center or the “F” Mark
Walter