Topic: Cb 750 k2 Valve clearance go up on hot engine

[olasek18_18@o2.pl]

I notice a strange thing. in my engine, I set the valve clearance exactly, intake valve 005, exhaust valve 008. after warming up the engine, I decided to check the clearance, because I could hear loud valves all the time - it turns out that it is larger than when cold - the intake valve is 0.10 and the exhaust valve 0.9.
Shouldn't it be that the valve clearances are reset on a hot engine? what could be the reason for this phenomenon?
Regards

[newday777]

Always check valve clearances on a cold engine(overnight at minimum)

[olasek18_18@o2.pl]

yes I know,
but is it normal that the valve clearance is not minimized on my warm engine?
I didn't put them on warm, just put off covers to check

[Don R]

 Aluminum and steel expand at different rates. Using mm, right? 

[HondaMan]

Yes, the cast iron of the valve stem grows less than the aluminum of the head's thickness. The result is more valve clearance on a hot engine. This is true with all aluminum engines: only some of the old automotive engines (cast iron heads and blocks) didn't do this. Those old engines used much larger clearance numbers, too, until the hydraulic lifters were invented, which self-adjust over a wide range to keep the clearances lower and quieter.

These ARE noisy engines when compared with later DOHC designs. That's normal!

[PeWe]

I set 0.10mm on both in and ex on my stock K2.
That to ensure that valves will close completely.

My modified K6 with hotter cam 0.10/0.15mm.
RC315/327 cams have 0.3mm lash!!

[olasek18_18@o2.pl]

Ok
Does it make sense to set the clearance to 'tight' then?
The motorcycle theoretically loses power after warming up because the valve does not open to the fully open position...

[PeWe]

No sense at all!
Better with more lash than less. If valve will not close completely due to no lash, seat and valve wear very hard and quick.
Exhaust valves will wear and like melt in the edges.

More lash, longer cooling time with valve in seat.

If head was refurbished with new valves, back cut valves could give a little better flow on low lifts. I do not know how much.

Lash on cold engine, it work from the very beginning when cold.

Those small numbers will not make any difference on lift and duration.

My K2 produced 58whp on dyno with almost stock engine except for Cruzinimage K7/K8 +0.50mm pistons, K7/K8 cam and Yamiya no numbers 4-4.
Lash 0.1/0.1mm as mentioned earlier.
Fresh head with new valves, guides. Race springs.

My more modified K6 has 0.15 mm lash on ex. Not sure it will produce more power with less lash giving higher lift  more and duration.
More duration, more overlap and less dynamic compression.

[willbird]

Ok
Does it make sense to set the clearance to 'tight' then?
The motorcycle theoretically loses power after warming up because the valve does not open to the fully open position...

I would not think that a few .001" less valve opening would give a measurable difference in HP.

I have seen V8 engine dyno tests where they used solid roller lifters on a hydraulic roller cam and gained single digit HP in an engine that made 600ish hp. In that case they were actually adding lash as you discussed...and they gained HP....probably due to better valve control due to the lighter lifter.

Bill

[Tracksnblades1]

No sense at all!
Better with more lash than less. If valve will not close completely due to no lash, seat and valve wear very hard and quick.
Exhaust valves will wear and like melt in the edges.

More lash, longer cooling time with valve in seat.

If head was refurbished with new valves, back cut valves could give a little better flow on low lifts. I do not know how much.

Lash on cold engine, it work from the very beginning when cold.

Those small numbers will not make any difference on lift and duration.

My K2 produced 58whp on dyno with almost stock engine except for Cruzinimage K7/K8 +0.50mm pistons, K7/K8 cam and Yamiya no numbers 4-4.
Fresh head with new valves, guides. Race springs.

My more modified K6 has 0.15 mm lash on ex. Not sure it will produce more power with less lash giving higher lift  more and duration.
More duration, more overlap and less dynamic compression.

Im more concerned with intake charge velocity than dynamic compression for wfo power.
It’s hard to see the inertia of an intense high velocity intake charge still filling the cylinder while the piston has changed directions and is moving up on the compression stroke. It’s free supercharging when everything is in harmony.
Cranking compression is a good tool though, but it’s at cranking speed. Long duration high compression engines with lower cranking compression will still have detonation concerns, especially with marginal fuel. It just usually happens at a higher rpm where the  long duration becomes a benefit instead of the detriment it causes at lower rpms…

It always a trade off

[olasek18_18@o2.pl]

EVERYTHING IS CLEAR, AS USUAL, YOU REPLYED TO MY OBJECTIONS
THANK YOU

[Don R]

 We have a 567" big block race engine. A couple years ago my engine guy in Indianapolis sold me a replacement cam (pits in the original one) that featured tighter lash and faster opening ramps. "Everybody was going to it" It dyno'ed about the same and started eating valvetrain parts.
 I was relieved when that cam ate a new lifter and I had to replace it. The extra heavy springs we were forced to use ultimately caused cracks in both aluminum heads, $5 or $6K later it's back to where it was. 
 The moral of this story is, even a seemingly small change can cause multiple other issues.

[HondaMan]

We have a 567" big block race engine. A couple years ago my engine guy in Indianapolis sold me a replacement cam (pits in the original one) that featured tighter lash and faster opening ramps. "Everybody was going to it" It dyno'ed about the same and started eating valvetrain parts.
 I was relieved when that cam ate a new lifter and I had to replace it. The extra heavy springs we were forced to use ultimately caused cracks in both aluminum heads, $5 or $6K later it's back to where it was. 
 The moral of this story is, even a seemingly small change can cause multiple other issues.

Hmm...sounds like the 750F2/3 top end story....

[PeWe]

Im more concerned with intake charge velocity than dynamic compression for wfo power.
It’s hard to see the inertia of an intense high velocity intake charge still filling the cylinder while the piston has changed directions and is moving up on the compression stroke. It’s free supercharging when everything is in harmony.
Cranking compression is a good tool though, but it’s at cranking speed. Long duration high compression engines with lower cranking compression will still have detonation concerns, especially with marginal fuel. It just usually happens at a higher rpm where the  long duration becomes a benefit instead of the detriment it causes at lower rpms…

It always a trade off

I really like your posts with details explaining how the engine  with carbs works and how to make it to work better!!

Easier to read than get to  know the hard way.

I remember the other thread where you convinced me that CV carbs are not that bad
Very quick responding flat slides not that relaxing....

[Floshenbarnical]

We have a 567" big block race engine. A couple years ago my engine guy in Indianapolis sold me a replacement cam (pits in the original one) that featured tighter lash and faster opening ramps. "Everybody was going to it" It dyno'ed about the same and started eating valvetrain parts.
 I was relieved when that cam ate a new lifter and I had to replace it. The extra heavy springs we were forced to use ultimately caused cracks in both aluminum heads, $5 or $6K later it's back to where it was. 
 The moral of this story is, even a seemingly small change can cause multiple other issues.

Hmm...sounds like the 750F2/3 top end story....

Please, stop it. I have nightmares about this happening to my bike 

[Tracksnblades1]

Im more concerned with intake charge velocity than dynamic compression for wfo power.
It’s hard to see the inertia of an intense high velocity intake charge still filling the cylinder while the piston has changed directions and is moving up on the compression stroke. It’s free supercharging when everything is in harmony.
Cranking compression is a good tool though, but it’s at cranking speed. Long duration high compression engines with lower cranking compression will still have detonation concerns, especially with marginal fuel. It just usually happens at a higher rpm where the  long duration becomes a benefit instead of the detriment it causes at lower rpms…

It always a trade off

I really like your posts with details explaining how the engine  with carbs works and how to make it to work better!!

Easier to read than get to  know the hard way.

I remember the other thread where you convinced me that CV carbs are not that bad
Very quick responding flat slides not that relaxing....

Likewise my overseas friend..you have already set the bar height many times..

I like the big mechanical ones too. With selective accelerator cams, pumps, squirters, nozzles, and time, you can make what you shouldn’t, work.

 Hell,  I still like Quadrajets...even the ones w/Solenoid idle (Eliminates dieseling on shut down) and assisted rpm during  AC compressor engagement in drive at an idle.. 😁 you know how they did it before the chip..

But you have to admit the laptop fuel curve changes are a lot less taxing on the skin and back..

It’s good to read Os18 eyes’ are open and is on point in his game. Many would not contemplate  the tight cold  valve clearances on an aluminum cylinder/ overhead cam configuration.