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steelcomp was here
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You can go .080" on intakes absolute min. but more is better..
Are you checking with checking springs in the heads or the actual running spring?
 

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You can go .080" on intakes absolute min. but more is better..
Are you checking with checking springs in the heads or the actual running spring?
Ok. I'll bite.Why so much as a minimum? The valve is chasing the piston down the bore, and I seriously doubt it can win that race, and its half way down the bore when the valve closes, were ther spring comes into play. So the only reason for so much clearance is valve bounce. And if you have that much, you should be looking at spring and pushrods. I can't see any reason for running more than total deck clearance plus .010. I can't imagine hitting an intake before you smacked the head. I have run .060 on a shit load of motors and never sweated it. Now the exhaust? Thats a whole other ball came.



 

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I have run .060 on a shit load of motors and never sweated it. Now the exhaust? Thats a whole other ball came.
You do have a point. My 2004 Engine Masters Engine because of time constraints had less than that....about lash + .010 :))eek:)) Never had a problem but it was only run on the dyno under very controlled conditions.

It was a case where .038" might as well have been 12 " a miss is a miss ;)

S CP :D
 

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Ok. I'll bite.Why so much as a minimum? The valve is chasing the piston down the bore, and I seriously doubt it can win that race, and its half way down the bore when the valve closes, were ther spring comes into play. So the only reason for so much clearance is valve bounce. And if you have that much, you should be looking at spring and pushrods. I can't see any reason for running more than total deck clearance plus .010. I can't imagine hitting an intake before you smacked the head. I have run .060 on a shit load of motors and never sweated it. Now the exhaust? Thats a whole other ball came.
X 2 GN7!!! I've seen my oldman run .060 (if he was lucky) on numerous occasions and the motor turned 8500+ with no problems. Like you mentioned, as long as you have a healthy valve train you shouldn't have anything to worry about.
 
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Discussion Starter · #10 ·
Well Saturday was a bad day in the shop. Nothing went right. The reason I asked was the How to hot rod BBC book showed the intake at .015 I and .020 E at 0 lash as the min. I thought that seemed tight. So yesterday I went back out and played some more with it. I come to really like the timing adjustment on this Jesel. Real easy. At 104 CL it's .078, at 106 CL it's .093 and at 108 CL it's .125. I guess I can run this thing anywhere I want. Has anyone run a BBC with less than 106 CL? Norm for me has been 108.

Tim
 

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Well Saturday was a bad day in the shop. Nothing went right. The reason I asked was the How to hot rod BBC book showed the intake at .015 I and .020 E at 0 lash as the min. I thought that seemed tight. So yesterday I went back out and played some more with it. I come to really like the timing adjustment on this Jesel. Real easy. At 104 CL it's .078, at 106 CL it's .093 and at 108 CL it's .125. I guess I can run this thing anywhere I want. Has anyone run a BBC with less than 106 CL? Norm for me has been 108.

Tim
Tim, just wondering, did you check the exhaust while you where retarding it? So, I'm assuming .015" without gasket? With a .043" gasket and .022" lash your at .080".
 

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steelcomp was here
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Ok. I'll bite.Why so much as a minimum? The valve is chasing the piston down the bore, and I seriously doubt it can win that race, and its half way down the bore when the valve closes, were ther spring comes into play. So the only reason for so much clearance is valve bounce. And if you have that much, you should be looking at spring and pushrods. I can't see any reason for running more than total deck clearance plus .010. I can't imagine hitting an intake before you smacked the head. I have run .060 on a shit load of motors and never sweated it. Now the exhaust? Thats a whole other ball came.
Like I siad, it depends on if that's with checking springs, or with running springs. Most guys check with checking springs, so I say min. .080. With running springs it can be a lot less. It can be net zero plus a RCH if you trust it, but VP is a safety margin, so it's relatively arbitrary. I think on something that you're trying to make maximum possible compression, it makes a difference. On something blown or where 3-3.5cc's doesn't matter, a little more is a little better, for safety sake.

Question...do you true-up your valve pockets to match the valve face angle?

Also, it's not just the distance of the valve floating that the clearance is for, it's also the time...while that vlave is floating, the piston is still moving, and while the valve may not actually "float" .080, it's still there when the pistion continues to move. A little more clearance just allows a little more "hang" time for the valve. At least that's my thinking on the subject.:)hand

Also...again...valve piston contact will depend on cam timing. I think most of the time the valve piston contact -range- may come after TDC. And FWIW, the piston and intake valve are converging, it's the ex valve and piston that are moving in the same direction.
 

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steelcomp was here
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X 2 GN7!!! I've seen my oldman run .060 (if he was lucky) on numerous occasions and the motor turned 8500+ with no problems. Like you mentioned, as long as you have a healthy valve train you shouldn't have anything to worry about.
Every engine has the potential for an over-rev, and to me, a little more clearance just insures that it's just a little more survivable. Valves hitting the pistons, especially if the pockets aren't true...you're done for the weekend. At least if the pockets are true, you won't bend the valve.
 

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Anyone know the minimun for the intake. In a BBC 468 N/A, 12.5:1, steel rods, 8000 rpm. Thanks

Tim
Question...do you true-up your valve pockets to match the valve face angle?

Also, it's not just the distance of the valve floating that the clearance is for, it's also the time...while that vlave is floating, the piston is still moving, and while the valve may not actually "float" .080, it's still there when the pistion continues to move. A little more clearance just allows a little more "hang" time for the valve. At least that's my thinking on the subject.:)hand

Also...again...valve piston contact will depend on cam timing. I think most of the time the valve piston contact -range- may come after TDC. And FWIW, the piston and intake valve are converging, it's the ex valve and piston that are moving in the same direction.
Yes I do actually match the pocket angle to the valve face when I need to fore clearance. That is what I thought was the cause of the KB piston failure I had in the enduro. I think we may be discussing different valves here. I agree the the intake is closest to the piston after TDC, and they are converging up TDC , Then piston decents, with the valve hot on it's ass, up to ABOUT 10* ATC. Then the piston pulls away. But "float" doesn't play into the game here. The intake is just starting to open, and it is being mechanically opened. It can't get ahead of the game. It can only get closer thru rod/piston assembly stretch, crank whip/flex, bearing failure etc. And it is very unlikely the they are going to get any closer with RPM, except by the above. As for the exhaust valve, They are moving in the same direction, and the valve is closeing by means of a spring and "float" does play a part in the clearance issue. I can't think of any way a INTAKE valve and piston can collide before the piston would hit the head, if the clearances are .010 greater than the total deck clearance



 

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steelcomp was here
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Yes I do actually match the pocket angle to the valve face when I need to fore clearance. That is what I thought was the cause of the KB piston failure I had in the enduro. I think we may be discussing different valves here. I agree the the intake is closest to the piston after TDC, and they are converging up TDC , Then piston decents, with the valve hot on it's ass, up to ABOUT 10* ATC. Then the piston pulls away. But "float" doesn't play into the game here. The intake is just starting to open, and it is being mechanically opened. It can't get ahead of the game. It can only get closer thru rod/piston assembly stretch, crank whip/flex, bearing failure etc. And it is very unlikely the they are going to get any closer with RPM, except by the above. As for the exhaust valve, They are moving in the same direction, and the valve is closeing by means of a spring and "float" does play a part in the clearance issue. I can't think of any way a INTAKE valve and piston can collide before the piston would hit the head, if the clearances are .010 greater than the total deck clearance
You're right...started mixing apples and oranges here...thinking and typing too fast. Sorry.
So do you intentionally run your intake VP so tight, or are you just saying you can get away with it?
 

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No, I don't set it that tight. It is usually a little more than that. But when you start pushing the CL foward, it gets a little tighter, but I don't concern myself with it so long as it is better than .060. To date I have been fortunate and have never had to cut an intake relief. Wish I could say the same for exhaust:)sphss



 
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Discussion Starter · #17 ·
Tim, just wondering, did you check the exhaust while you where retarding it? So, I'm assuming .015" without gasket? With a .043" gasket and .022" lash your at .080".
Vince, I did check the exhaust at 108. I knew their clearance would be bigger as the CL went down. At 108 I could measure it with a yard stick. LOL It is .250. The intake pocket seems to be the same angle as the valve.

Tim
 

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Vince, I did check the exhaust at 108. I knew their clearance would be bigger as the CL went down. At 108 I could measure it with a yard stick. LOL It is .250. The intake pocket seems to be the same angle as the valve.

Tim
LOL!!! I was just curious!!! Hope you get her back together soon!!!! As far as running it that far advance, I haven't and as far as I know my oldman hasn't either.. It would be interesting to see what effects it has on the boat... I'm sure someone has tried it on a DYNO!! I've never had that luxury!!
 
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