valve train geometry

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valve train geometry

Post  460Dave on February 10th 2012, 11:01 pm

Help! My push rod is hitting the rocker arm at the top of lift on the intake valves.

Ok ... specifics.

P-51 heads
Comp Cams mech roller .657 .668 cam with their recommended springs (I don't remember the part number)
Trick Flow 3/8 push rods
Howards 1.73F rockers

When I rotate the engine, the intake push rod contacts the backside of the rocker and flexes the push rod toward the centerline of the engine. Has anyone seen this before? Is it an indication of something wrong (other than the rocker arm)?

Ok, after some thought, it has to be that my push rod is too long. I will do some measuring and verify where the rocker is riding on the valve.

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Re: valve train geometry

Post  richter69 on February 11th 2012, 12:14 am

how long are they?
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Re: valve train geometry

Post  rmcomprandy on February 11th 2012, 12:52 am

460Dave wrote:Help! My push rod is hitting the rocker arm at the top of lift on the intake valves.

Ok ... specifics.

P-51 heads
Comp Cams mech roller .657 .668 cam with their recommended springs (I don't remember the part number)
Trick Flow 3/8 push rods
Howards 1.73F rockers

When I rotate the engine, the intake push rod contacts the backside of the rocker and flexes the push rod toward the centerline of the engine. Has anyone seen this before? Is it an indication of something wrong (other than the rocker arm)?

Ok, after some thought, it has to be that my push rod is too long. I will do some measuring and verify where the rocker is riding on the valve.

The pushrod is definitely too long no matter where your rocker is riding on the valve tip.

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Re: valve train geometry

Post  460Dave on February 11th 2012, 12:16 pm

Ok.. The intake push rods are 9.25 long. The exh. are 9.00. All valves have the same wear pattern. The engine is still brand new. It has run less than 5 minutes ( a couple at a time) The pattern on the intake looks really nice (see pic). What is a "normal length for an intake pushrod? If I shorten it, how might that change my contact pattern?

FYI - I am a bit concerned with the exh. pattern as it is heavy on one side and extremely light on the other. (on all valves) (see pic). It looks like the rocker angle is off a hair. Has anyone else seen this with the P-51s?

https://picasaweb.google.com/117409403657915074198/20120211?authkey=Gv1sRgCO34oISUp5D1YA#


I began looking at things when I was having trouble with the starter turning the motor over. I can turn the engine by hand with a 1/2" breaker bar on the crank. It's tight, but not excessive for a new engine. It spins, but acts like it has a low battery. I eliminated battery and wiring issues by putting a short battery cable (2 ft) directly from starter to the battery and from battery to engine block. (I set the battery on the ground under the starter.) It still wouldn't turn over. I have started the engine 1/2 dozen times over the last couple of weeks, and it has gradually gotten where it won't turn over at all. Yep, tried 3 different batteries (one brand new), removed spark plugs, etc. No change. Can the starter just be weak? The starter is a new DB Electric.

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I think I figured it out.

Post  460Dave on February 11th 2012, 12:49 pm

This is what I get for posting before thinking. When I did my final assembly, I put the intakes on the exhaust and vice versa. Now I get the privilege of looking like a dumb ass in front of everyone. Yeah!

Before you put too much thought into my starter issue, I guess I should do some more troubleshooting on my end. I'm sure it has something to do with my attention to detail deficit.

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Re: valve train geometry

Post  richter69 on February 11th 2012, 12:51 pm

mine are 9.100 and 9.300, it could be the rocker arm itself, I'm not familiar with those.

I did have to clearance my old Lunati rockers just a tad in the same area as yours look to be touching, but this was a .800+ lift deal with a 7/16" pushrod. The new Crower stainless I have on it now clear fine..........its all about the size of the rocker body and the dist from the cup to the fulcrum.
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Re: valve train geometry

Post  KY JELLY on February 11th 2012, 1:57 pm

What are the valve lengths ?
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Re: valve train geometry

Post  stanggt on February 11th 2012, 4:53 pm

I had an issue with some Milodon rollers when I first bought my SCJ Kaase heads and after I did some research I found that Harland Sharp makes a head specific rocker arm for those heads so I bought a set and they fit perfect, no issues and stay towards center of tip through full rotation where as my other ones ran right to the very edge of stem no matter where I adjusted the rod length even with 2" arm studs. I assume that the P51 are the same as SCJ when it comes to valve placement. I was running a slightly bigger camshaft as yours also. If that helps at all, just sharing what I found.
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Re: valve train geometry

Post  rmcomprandy on February 11th 2012, 5:08 pm

stanggt wrote:I had an issue with some Milodon rollers when I first bought my SCJ Kaase heads and after I did some research I found that Harland Sharp makes a head specific rocker arm for those heads so I bought a set and they fit perfect, no issues and stay towards center of tip through full rotation where as my other ones ran right to the very edge of stem no matter where I adjusted the rod length even with 2" arm studs. I assume that the P51 are the same as SCJ when it comes to valve placement. I was running a slightly bigger camshaft as yours also. If that helps at all, just sharing what I found.

The intake rocker stud on a P-51 head is on a different angle than that of an SCJ.

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