79 R65: Valve adjustment... engine hot or cold

[67siia]

As I recall, applicable to other bikes, the rule of thumb is to adjust the valves with a cold engine..... is it the same case with the R65, engine cold to check & adjust valves?

[Tony Smith]

As I recall, applicable to other bikes, the rule of thumb is to adjust the valves with a cold engine..... is it the same case with the R65, engine cold to check & adjust valves?

The measurements quoted in nearly all publications I have seen are COLD clearances. I have had the misfortune to have once owned a vehicle that required hot setting of valve clearances which was a pig of a job. I ended the nonsense by carefully setting the clearances hot and then measuring them cold. Next time I set them cold, warmed the car up and measured the hot clearance - never set them hot again.

[Barry]

I always do them cold. Duane Ausherman  says it doesn't make a great difference Hot or Cold. You wouldn't do them hot but maybe it isn't so critical that the engine is stone cold. It would be easy to do an experiment to confirm if this is true. I kind of like working on an engine that still has a little warmth.

Back in the mid 70's I had a Vauxhall pushrod engine where the clearances were checked with the engine running. It was a messy job with oil flying about and it sounds crazy but I swear it's true. I've just Googled it to make sure my memory wasn't playing tricks after 40 years.

My vote for easy valve clearance goes to a 50's or 60's Matchless single where the clearances were set to zero by checking if the pushrods would still spin between your fingers.

[montmil]

ALWAYS COLD.

Heat will cause the valve lash components to "grow / expand" so after the bits cool, your lash settings will be loosey goosey and will make too much BMW Music.

[Barry]

The thing about valve clearances is the exact gap really isn't that critical in the sense that a 1 thou error won't make any noticeable difference to the way the engine sounds but it will make a difference to the way the engine runs if there is a couple of thou variation between cylinders. So what's important is striving to set both cylinders as close to the same as possible. Whatever setting is used a consistent technique is needed. One important aspect of technique is to take up any slack/oil film in the valve train by pressing on the end of the adjuster with your thumb using moderate pressure. The affect that has on feeler gauge drag will be easily felt and aids consistent settings. For me using a consistent technique is probably more important than the engine being absolutely stone cold and stressing about the difference that temperature will make to the exact clearance. The exact clearance isn't important as long as both sides are the same.

I don't know what anyone else does but when servicing the bike I start with the engine hot to drain the engine and transmission oils. Then I remove the front cover and spark plugs so I can rotate the crank with an Allen Key in the rotor bolt and do a static timing check. By the time I've set the timing, changed the filter and refilled the oils and had a brew the engine is cold enough to meet my definition of cold and I then do the valve clearances. To wait for stone cold would probably mean waiting to the next day and a BMW dealer wouldn't do that.

What I'm suggesting is if setting the clearances with the engine luke warm makes some very small difference, lets say half a thou although I doubt it's that much, it really doesn't matter as long as it's half a thou on both cylinders.

[Luca]

Sure sounds like somebody more ambitious than I is going to set their valves cold and measure them hot in the near future  




MY brother told me about a valve setting procedure for an old domestic car.  I think it was a Chevy.  As I recall, you had the engine running and tightened the valves up (they loosened with time) until they "quieted down"

[Bob_Roller]

Just to throw this out there, what clearances are you going to set your valves to

[Tony Smith]

Back in the mid 70's I had a Vauxhall pushrod engine where the clearances were checked with the engine running. It was a messy job with oil flying about and it sounds crazy but I swear it's true. I've just Googled it to make sure my memory wasn't playing tricks after 40 years.

In Australia the local GM-offshoot "Holden" the majrity of which were powered by a semi-indigenous designed "Red Motor" of varying capacity (depending on model) from 138c.i. to 202c.i. They "featured" hydraulic tappets which were adjusted exactly as you describe. Fortunately they usually only required one adjustment after a rebuild and were other wise very reliable. The only drawback (to a young "lad about town" such as myself) was that at around 5,500rpm they tended to "pump up" causing valve float and (from my point of view) a curtailment of fun.

Anyway, setting the initial valve lash was accomplished by starting the engine and winding each valve adjuster out till the tappet rattled and then winding in until the engine missed, the point 1/2 way between the two was perfect adjustment. Much oil was shed in the process, I used to wear old clothes and perform the operation in the yard rather than in the car port.

My vote for easy valve clearance goes to a 50's or 60's Matchless single where the clearances were set to zero by checking if the pushrods would still spin between your fingers.

Tish and Tosh! CB500T were even easier - courtesy of torsion bar valve springs adjusted by a lock-nutted eccentric they were adjusted as per the engines we were discussing above. You could set all four (4) tappets in under 2 minutes, Matchless were quick, but not thatquick.

[Luddite]

CB450 same deal with the torsion bars, at least the '72...I'm a newbie by the way, but as we say in these parts this site is "Wicked Pissa!"

[Tony Smith]

CB450 same deal with the torsion bars, at least the '72...I'm a newbie by the way, but as we say in these parts this site is "Wicked Pissa!"

I envy you your Brown Bomber, I wish I still had a CB450/500T but they have passed into collector land and are way too expensive now. While I am still misty eyed, I'd love a good SL350 too. Friend of mine had one that had a significant portion of his yearly income invested in Yoshimura components for it, the thing was demon quick and embarrassed many a young man of CB750s, Z1s and the like, the downside was that he had to run a mechanical hour meter and throw valve springs away after 2 hours, rings after 5 hours and engine bearings every 10 hours. Eventually he overlooked one of Yoshimura's requirements and it self destructed in a spectacular and irretrievable way

[Barry]

Sure sounds like somebody more ambitious than I is going to set their valves cold and measure them hot in the near future
 

OK I suppose I better do it in support of what I was saying.  I'm not doing it hot though and risk getting a burn, that would be silly.

When I got home from work today I left the bike exactly one hour to cool and then carefully measured the clearances on the left cylinder. The engine was warm to the touch but not hot. You could safely hold a hand on it indefinitely.

I deliberately run wide clearances so the measurements were what I set them at last time:

Tight .009" Exhaust
Tight .006" Inlet.  

My definition of tight is the gauge will go in but without pressure on the end of the adjuster the gauge is grabbed tight and will only slide still with some resistance when pressure is applied. If the gauge will slide easily you didn't measure anything and all you know is the gap is bigger than the gauge.

So I'm going to leave it another 5 hours making 6 in total and measure again. If I'm not satisfied the engine is really cold I'll leave it overnight and measure in the morning before I go to work - good job it only takes a few minutes to button up again.

Watch this space.
  

[Barry]

After 6 hours I judged the engine to be stone cold and measured again.

I couldn't detect any difference which I would suggests means the clearances couldn't have changed from warm to stone cold by more an half a thou.

While I understand that waiting for stone cold has always seemed the right thing to do this shows it to be unnecessary and including valve clearances in a normal service time frame from a hot start is perfectly reasonable.