PCV issue

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Im gonna mention what the comp cams tech guys told me when I was having issues, he said believe it or not when the engine warms up the clearances on the valves actually got bigger....so set them tighter cold...this is in dads 273, solid cam/lifters, doesnt sound right to me but thats what the tech guy said. Maybe give them a call?? Couldnt hurt. Good luck, post your results/findings
 
toolmanmike said:
I re-read this thread and I see you have a 318 with a solid lifter cam and of course adjustable rockers. Valve lash does some goofy things with these engines. I have used different specs for my 273 and it runs best when I adjust them on the loose side of spec. The motor is pretty noisy when I start it cold and quiets down a bit at operating temp but here is still a bit of clatter even when warm. It seems to like it that way. It is crisper and revs easier. tmm
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X2 tmm.
 
toolmanmike said:
I re-read this thread and I see you have a 318 with a solid lifter cam and of course adjustable rockers. Valve lash does some goofy things with these engines. I have used different specs for my 273 and it runs best when I adjust them on the loose side of spec. The motor is pretty noisy when I start it cold and quiets down a bit at operating temp but here is still a bit of clatter even when warm. It seems to like it that way. It is crisper and revs easier. tmm
Click to expand...

Adjusting the lash looser is kinda like putting in a slightly smaller cam. More lash means less lift and duration. Old racer's trick to tune their engines for a particular track is to vary the lash. Maybe your particular engine, being a small one, would like a smaller cam. Or it's possible that if you tighten the lash and tune the rest of the engine for it it'd run better yet.
 
4spdragtop said:
Im gonna mention what the comp cams tech guys told me when I was having issues, he said believe it or not when the engine warms up the clearances on the valves actually got bigger....so set them tighter cold...this is in dads 273, solid cam/lifters, doesnt sound right to me but thats what the tech guy said. Maybe give them a call?? Couldnt hurt. Good luck, post your results/findings
Click to expand...

Are you running aluminum heads? If so that's why. Aluminum grows more than iron so aluminum headed engines need less cold lash. I haven't verified that but it's what Bullet cams told me. I have checked my iron headed solid cammed 408 both hot and cold and it tightens up when it warms up.
 
fishy68 said:
Are you running aluminum heads? If so that's why. Aluminum grows more than iron so aluminum headed engines need less cold lash. I haven't verified that but it's what Bullet cams told me. I have checked my iron headed solid cammed 408 both hot and cold and it tightens up when it warms up.
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Yep. Lash gets tighter when the engine gets hot. The lash changes the lift slightly. Correct me if I'm wrong but the lift should be effected by multiplying the difference in lash by 1.5 (rocker ratio) Just say instead of .020 lash you set it at .015 (.005 x 1.5 = .0075) You would increase the lift of your .450 lift cam to .4575. Not a lot but it could make a slight difference in the way it runs. The most important thing about valve lash is keeping a clearance between the valve stem and the rocker tip when the engine is at operating temp. If the valves are set too tight, they stay open and especially the exhaust valves can get hot enough to burn if they don't close to the seat. tmm
 
I'm of the belief that the pushrod expands in length more then the other factors and that's what primarily tightens the lash....but i could be completely wrong?

Wonder if any one has done a experiment heating a pushrod form say 70 deg. up to about 250 and measured the difference in length?

Just bench racin'.......great posts guys.

P.S. Steel expantion was also referenced in Post #16. Sorry Redfish, i should have mentioned your post.:smile:
 
That would be a fun experiment Rick. I wish I had a 8" dial caliper on my tool truck. LOL
 
I have a couple 6" inchers. I had to borrow a 8" one from my neighbor when I measured for my pushrods.
 
I went .016 Intake and .025 Exhaust (cold). I also went 4% richer with different metering rods in the carb (richer for the low power setting). I also installed a new PCV valve with a new seal in the cap. It seems to idle better and run better at low RPM's. I think you guys were spot on with the lean issue. I'm thinking the PCV valve change and metering rod change helped with the lean condition. As of now, I'm happy how it runs. Thanks Again!
 
I also forgot to mention that I have cast iron heads. Below is somthing I found during a search of the web for an answer about lash:

You can take the "hot" setting given to you in the catalog or cam specification card and
alter it by the following amount to get a "cold" lash setting.

With iron block and iron heads, add .002"
With iron block and aluminum heads, subtract .006".
With both aluminum block and heads, subtract .012".

http://www.wallaceracing.com/valvelash.htm
 
OldmanRick said:
I'm of the belief that the pushrod expands in length more then the other factors and that's what primarily tightens the lash....but i could be completely wrong?

Wonder if any one has done a experiment heating a pushrod form say 70 deg. up to about 250 and measured the difference in length?

Just bench racin'.......great posts guys.

P.S. Steel expantion was also referenced in Post #16. Sorry Redfish, i should have mentioned your post.:smile:
Click to expand...

That is something to consider. I have an extra pushrod and a heat gun and 8" caliper so I'll try that experiment sometime in the near future and see what happens and post the results.
 
1966273Valiant said:
I also forgot to mention that I have cast iron heads. Below is somthing I found during a search of the web for an answer about lash:

You can take the "hot" setting given to you in the catalog or cam specification card and
alter it by the following amount to get a "cold" lash setting.

With iron block and iron heads, add .002"
With iron block and aluminum heads, subtract .006".
With both aluminum block and heads, subtract .012".

http://www.wallaceracing.com/valvelash.htm
Click to expand...

Glad you got it doing better Valiant. Those are the same figures Bullet cams told me when I used one of their cams and called to ask about the cold lash setting.
 
fishy68 said:
That is something to consider. I have an extra pushrod and a heat gun and 8" caliper so I'll try that experiment sometime in the near future and see what happens and post the results.
Click to expand...

That would be cool fishy. I don't have either right now to do a test. I'm sure the cam companies have that kind of info. but it would be nice to see the results from one of us:thumleft:
 
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