Solid vrs roller cam on a street motor

[F1Fever]

shouldn't the goal really be designing cams with tighter lash? or possibly a hybrid lifter that only uses a spring (a stiff spring) and doesn't rely on oil pressure to pump it up?

[MadBill]

Hi, bill,

Not following you here on the effect of a rev kit on lash point. If the lifter and pushrod are held against the cam, wouldn't all of the lash slack be under the tin cover at the top between the pushrod and rocker?

thnx, jv.

With the 'MadBill rev kit variant' Jack, the upper end of the springs seat not against a plate on the underside of the head, but on seats (high-grade washers) pressed on to the lower portion of the pushrods. Thus, the push rod is raised against the rocker, and the lifter forced down onto the lobe during the valve closed portion of the cycle, without the need for a heavy spring, complex, sometimes tricky to install or even unavailable, traditional rev kit. The spring pressure would be low enough to hold the rocker up by hand while setting the lash.

(I've likely overlooked some vital factor as usual, can't wait to find out what! )

[mudracer]

I recall a thread that I read on here a while back regarding the lifter galleys on a big block chevy. Seems that the oil galley was being blocked off by the lifters, and starved the lifters for oil at lower speeds.

IF this is the case, what modifications would you recommend to the block to ensure longevity?

Are there any modifications to the lifter that would allow oil flow through the galleys to promote a more positive lubrication circuit? Or should oil be sent to both ends of the oil galley?

I know some blocks have locations at the front of the engine to lube the oil galley at the cam. Are they beneficial, or are these ports not conducive to oiling the cam as a benefit.

[PackardV8]

Hi, Bill,

Thanks for the clarification on the MadBill deviation. Now I get the concept and I like the idea a lot. When are you going into production?

If a tapered pushrods were properly sized, a beehive retainer would slide up and lock in the appropriate location.. The bottom end of the spring would be sized to locate inside the lifter. No locating plate required. Too simple?

thnx, jv.

[F1Fever]

this is the easy way.

[MadBill]

Yes! And the spring could be a simple Bellville washer...

[iadr]

I recall a thread that I read on here a while back regarding the lifter galleys on a big block chevy. Seems that the oil galley was being blocked off by the lifters, and starved the lifters for oil at lower speeds.

viewtopic.php?t=5460&highlight=oiling+solved



*

Yes, I, too, can see the rollers w/o a rev kit 'skidding' on the base circle and then having to re-accelerate during the opening...Hmm.

[torquefan]

excuse the possibly silly question, but: if a solid roller cam is supposed to have .015 - .020 or more lash, but you use a rev kit to keep the roller on the cam, why not just set the lash tighter? that leads to another question. can you set the lash too tight (of course without holding the valve open) it seems to me the main difference between solid and hydraulic is the fact the hyd. is in constant contact with the lobe instead of having .020 worth of gap to take up negating any opening ramp's benefit.

[ClassicComp]

Fontana midget engines have the rev kit springs held down by the pushrods

[MadBill]

Fontana midget engines have the rev kit springs held down by the pushrods

Wouldn't you know! It's so true that "There's nothing new under the sun." Still, it means some one's worked out the bugs and us street freaks may reap the benefit..

[MadBill]

excuse the possibly silly question, but: if a solid roller cam is supposed to have .015 - .020 or more lash, but you use a rev kit to keep the roller on the cam, why not just set the lash tighter? that leads to another question. can you set the lash too tight (of course without holding the valve open) it seems to me the main difference between solid and hydraulic is the fact the hyd. is in constant contact with the lobe instead of having .020 worth of gap to take up negating any opening ramp's benefit.

The lash is required to allow for thermal expansion/contraction of the block, heads, valves, etc., as well as changing clearances due to wear between service intervals. It can't easily be accurately determined even on a hot engine [Valve burning in fifties-era Chev race engines was eventually traced to inadequate actual running lash holding the valves off the seats, prompting the Duntov "30-30" cam design (referring I believe to 0.030" cold clearance, up from the previous 0.012", IIRC.)]
The

[F1Fever]

I sure miss the old 30-30's I had a 350 in a GN when I got out of HS with a Victor jr and Duntov 30-30...man that was a fun car.

[torquefan]

excuse the possibly silly question, but: if a solid roller cam is supposed to have .015 - .020 or more lash, but you use a rev kit to keep the roller on the cam, why not just set the lash tighter? that leads to another question. can you set the lash too tight (of course without holding the valve open) it seems to me the main difference between solid and hydraulic is the fact the hyd. is in constant contact with the lobe instead of having .020 worth of gap to take up negating any opening ramp's benefit.

The lash is required to allow for thermal expansion/contraction of the block, heads, valves, etc., as well as changing clearances due to wear between service intervals. It can't easily be accurately determined even on a hot engine [Valve burning in fifties-era Chev race engines was eventually traced to inadequate actual running lash holding the valves off the seats, prompting the Duntov "30-30" cam design (referring I believe to 0.030" cold clearance, up from the previous 0.012", IIRC.)]
The

thanks for the reply. i understand that you need some clearance. but .020 or more? with the subtle nuances of a cam lobe, can't that mean the lifter may "slam" into the opening ramp? that leads me to the next question that i forgot to ask in my last post: why not set it cold? i've done searches, read various magazines, etc. and can't seem to find an answer---so i set mine cold allowing for expansion and so far have not had any problems. i do double check the hot clearance and it has always been within a couple thousandths. i'm talking mild street roller cams bythe way.

[F1Fever]

The cam is designed for XX lash, each engine is different, different pushrods, block, heads, rockers, they all expand at different rates. from aluminum to iron and brand to brand.