Problem with performance after cam.

[Guantero]

Ok, so got the motor back together and no real difference so I know it is not and was not a tooth off. One thing I read is that if the push rods are too long, it will cause this problem. I see that it will also cause louder lifters which I think I have a little bit. I do hear a ticking/tapping noise a little but thought it might be just because of the new headers too. I pulled a few push rods out and even though they say on them 7.400, they measure about 7.420-7.425. My stock ones are 7.393 to 7.397. would that be enough to cause a problem? I know in these motors they have the hydrolic lifters but I don't know how much fudge factor they can deal with.

 

Thanks

Scott

[Doug_Scott]

Your push rods are about 0.032 longer max. The amount of lifter preload required is usually between 0.020" and 0.060". I do not see how a too long push rod can cause lifter tick. Too short will do that, but not too long. According to info I found online, the LS series of engines are interferance engines, and having no room left in the hydraulic lifter can cause valve to piston issues. Valve adjustment is done via pushrod length. You may find that the engine builder put longer pushrods in to get the correct preload on the lifters. Were the heads taken off, and if so, where they resurfaced?

 

Did you try degreeing the cam?

 

Can you find out if you camshaft was a new core or a regrind? A regrind cam will require longer pushrods due to the base circle being smaller.

[Guantero]

The heads were not off the motor and I think I will get an adjustable timing set and have this mechanic that I know help degree the cam. I think that is all that is left. The cam is a new core so it has a full size base circle and stock push rods should work. As far as I know, this cam should be install staight up and not advanced. I will try that and see if that works. Anyone have any recommendations on a timing set?

 

Thanks

Scott

[Guantero]

Ok, I did the valve lash check that thunder racings mechanic recommends (IOEC). Stock length is supposed to be 7.400 and mine are 7.393-7.397 so pretty close. The ones they sent me say 7.400 and measure around 7.420. they say take up the lash and torque to get 1.25 to 1.75 turns from zero lash to torque. Too few and you need longer rods and too many and you need shorter rods. With stock rods, I got 3/4 turn. With their aftermarket rods I got 7/8 turn. According to that, it means I need rods at least 7.425. Does that make sense being I didn't pull the heads or change anything else? Could that be my problem all along? Should I order 7.425 or 7.450? Using a feeler guage to try and simulate what I really need, I should need around 7.432. I know that the rods are not always what they are advertised as and tend to be long.

 

Thanks

Scott

[Doug_Scott]

I am not sure I am understanding what they are saying. LS engine is supposed to not have adjustable valve train. The proper lifter preload is supposed to be a result of torquing the rocker stands to factory spec. After doing some reading online I see it is suggested that valves be torqued when lifter is on base circle of cam.

 

The only reason the clearance will be different to what was stock is a difference in dimension of one of the components changed. For example, since the head was not touched, rocker arm, pedestal, and valve stem height will be exactly the same as before the cam change. If you are using the original push rods, then the only parts that can change clearance are the cam and lifters. If the cam is using stock base circle specs, then only the lifter can be causing the change in clearances. Are the lifters stock type? i found a document from Crane in regards to properly adjusting their roller rockers on the LS engine, I realize you do not have these, but, take a look at the procedure and see if it helps you.

 

http://www.vincihiperformance.com/LS1%20ROLLER%20ROCKER%20ADJUSTMENT%20INSTRUCTIONS.HTML

 

Did you try degreeing the cam in? That may also show you any clearance abnormality as well.