K75 valve clearance question

[jimmyenglish]

Hey everyone. I have a 93' k75 with 60k on it. I checked the valve clearance at 45k. The intakes were all good but the exhaust were all .12 to .15. I wondered how could all three be so grossly off and figured there must be something different about my bike. Runs great anyway

So I checked it again today and I couldn't help but wonder how this can be? THe specs were the same: all the intakes at .15ish but the exausts at .12ish, .15 and again .12ish. I thought that valve clearance typically got greater with age? If one's valve adjustment is out of whack how does it affect engine operation? Thanks in advance! Great forum!

[98lee]

Your intakes are right on. Your exhausts are desperately in need of adjustment. Very typical.

The intakes rarely need adjusting. As you surmised, the only thing that changes them is wear. They are very well lubricated.

On the other hand, exhaust valves (and seats) have to deal with tremendous temperatures. What changes the exhaust clearances is a process called valve recession. That is the valve literally sinks deeper and deeper into the head (seat), thereby closing up the clearances on the cam end. This gives less seat time to cool the valve which increases the rate of recession.

Eventually the clearances get so little that when the engine heats up the exhaust valve never completely closes, leading to poor idle, stalling, poor power and burnt valves.

Fix it now! Then resync the throttle bodies. You will be amazed how much stronger (especially at high RPM) and smoother it will be. You will find out why people who have good running K75s get hooked on them.




Intake: 0.15-0.20 mm (0.006-0.008 in.)
Exhaust: 0.25-0.30 mm (0.010-0.012 in.)


If you have to make an adjustment shoot for:
Intake: 0.15mm (0.006 in.)
Exhaust:0.30mm (0.012 in.)

Tight side of spec on intake and loose side of spec on exhaust.

All measurements COLD (head temp less than 95 deg.F.)


:dance :dance :dance

[jimmyenglish]

Thanks for such a great response Lee. I'll adjust them accordingly and post the results. Looking forward to it.

[roy]

Remember, as these valves wear the clearances decrease.

Roy

[98lee]

Remember, as these valves wear the clearances decrease.

Roy

Actually it's the valve/seat interface, and pretty much just the exhausts.

If you think wear, you usually would be thinking cam, follower, and valve tip wear, which would logically increase clearances. This type of wear is VERY minimal on these engines. That is why I try not not refer to it as wear, although it actually is.

When you describe it as valve recession (the valve receding into the head, getting CLOSER to the cam), then it becomes clearer why the exhaust valves clearance decreases, and needs to be adjusted (increased).

When you take into account the radically different temperatures at the intake valve/seat interface (continually being cooled by the cool air/fuel mixture flowing by it), versus the extreme heat at the exhaust valve/seat interface heated by the 1300 deg.+ exhaust gases, it's pretty easy to grasp why the exhaust valves are the ones that suffer and not the intakes.

OR to put it another way:

As these valves wear the clearances decrease.:thumb


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[deilenberger]

Lee said:

Fix it now! Then resync the throttle bodies. You will be amazed how much stronger (especially at high RPM) and smoother it will be. You will find out why people who have good running K75s get hooked on them.
On "resync" the TB's - typically - if the inter-throttle-body screws haven't been messed with LEAVE THEM ALONE. The only adjustments that should be made on the TB's are the brass idle-bypass screws, and the basic idle adjustment screw, and finally the throttle-position-switch.

Unfortunately - there was some IMHO bad tech posted on the IBMWR website for a number of years - suggesting that adjusting the inter-throttle-body-screws was a good thing. It wasn't. The throttle-body assembly is setup on a flow bench, and should stay in adjustment for the life of the bike.

On a K bike where the valves are set correctly - the factory adjustment should result in equal vacuum on all cylinders at any RPM above about 2k. If this isn't true - something else is wrong, and tweaking the TB's to "correct" it - is hiding the problem, not fixing anything.

Once the valves are done.. Remove and clean the brass adjusting screws. Replace the O rings on them if they look at all questionable. Put them back in the throttle-bodies, and gently tighten them until they bottom out.. then turn out ONE turn. With a set of vacuum gauges (or mercury sticks) hooked to the vacuum ports on the TB's - adjust the brass screws for equal vacuum at idle. Very little adjustment should be needed. Then set the idle speed to 1,000-1,100 RPM. Finally - rev the engine, the vacuum should be the same across all 3(or 4) cylinders. If it isn't - and the valves are adjusted - look for vacuum leaks at the mounting point of the TB's to the head.

[98lee]

When I said resync throttle bodies, I was referring to:

With a set of vacuum gauges (or mercury sticks) hooked to the vacuum ports on the TB's - adjust the brass screws for equal vacuum at idle. Very little adjustment should be needed. Then set the idle speed to 1,000-1,100 RPM. Finally - rev the engine, the vacuum should be the same across all 3(or 4) cylinders. If it isn't - and the valves are adjusted - look for vacuum leaks at the mounting point of the TB's to the head.


Under no circumstances should the throttle linkage screws (with the blue anti tamper paint on them) be touched!

I probably should have more correctly used the term rebalance. I guess I got sloppy because the manometer that I use is called a carb-sync pro. Sorry if there was any confusion.

Thanks for pointing that out Don.

Now could you tell Ragman on "New (used) Brick" how to adjust the valves on his K1100?


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[deilenberger]

Under no circumstances should the throttle linkage screws (with the blue anti tamper paint on them) be touched!

I probably should have more correctly used the term rebalance. I guess I got sloppy because the manometer that I use is called a carb-sync pro. Sorry if there was any confusion.

Thanks for pointing that out Don.

Now could you tell Ragman on "New (used) Brick" how to adjust the valves on his K1100?

:dance :dance :danceLee, no problem. I also forgot to mention on checking the TPS (throttle-position-switch)..

Put your good ear :) down next to the rear of the throttle bodies, and use your hand - ignition off - to slightly open/close the throttle. You should hear a faint "click" from the black box on the end of the throttle bodies - just as the throttle starts to open. If not - it may need adjusting (and we'll leave that alone until someone asks how.. it's fairly self-evident.)

For the later model 4 valve engines - the cams must be removed and the buckets replaced to adjust the valve clearances. I've never done it, and actually it apparently is very rare that it needs doing. I'm sure someone here can fill us in on it..

Best,

[roy]

As Don stated you need to remove the cams to change the buckets on the 4-valve engines. I have done this on my K1200LT but I would not attempt to tell some one how to do this who does not have a service manual. To much chance for engine damage if one little misatake is made. There is a prescribed sequence for loosening and tightening the cam bearing caps etc.

I will say this. It is more time consuming than difficult. I would allow at least 4 hrs minimum to remove the cams and replace them. I prefer slow and careful Vs fast and O* Sh*t!!!

Roy

[dswilliams47]

Intake: 0.15-0.20 mm (0.006-0.008 in.)
Exhaust: 0.25-0.30 mm (0.010-0.012 in.)


If you have to make an adjustment shoot for:
Intake: 0.15mm (0.006 in.)
Exhaust:0.25mm (0.012 in.)

Tight side of spec on intake and loose side of spec on exhaust.


Something doesn't look right here. You say to go tight on the intake and loose on the exhaust but you recommend the tight clearance on both. Which way is it?

Dave

[98lee]

Sorry for the bad proof reading. I got the inch spec correct on the exhaust right , but the metric should read 0.30mm.

Once again, I apologize. I've been very distracted by some events that transpired yesterday and Friday.


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