push rod length questions
 

I have a 502 Mag MP that we freshened up a few moths ago and I went with a bigger cam , Crower lifters, and had the ecu re-flashed as well. My question is, how will it effect the valve lift and the valve timing if the push rods are a little on the long side? We marked the top of the valve and rolled the motor over and roller seemed to be traveling on the bottom side of the valve stem and when we checked the fulcrum (spelling) the push rods were top long according to the tool we used! Another question I have is how will this effect the over all performance of the motor, will I get the max lift of .542 on the intake valves and the .535 on the exhaust valves?

Thanks for the help,

It will side load the valve which will cause the guides to wear quickly. Your lift will be fine as long as its staying on the top of the stem.

I was told by running a long push rod I would lose some valve lift, didn't know if anyone has run into this problem or not, thanks

Here is a article RMbuilder sent me when I adjusted mine. http://www.popularhotrodding.com/eng...variables.html

Go to www.mid-lift .com and that will explain everything.

The only way that you will change the amount of lift of the cam is to physically change the cam. If the pushrod is to long or to short, you will prematurely wear the guides as Blue Thunder said. You will still have the same amount of lift with the right pushrod or the wrong one. You really need to get it fixed.
Eddie

Or a 1.8 rocker arm instead of the regular 1.7, it will give slighly more valve lift. Gotta check clearances though.

I know some guys who are running 1.8's on the exhuast side to give a little more flow and act like a split duration cam on crappy heads.

I run 1.8's on my intake side for more lift, and 1.7's on the exhaust. This was done on a dyno and there were only gains for my setup on the intake side.

I believe if the geometry is too far off, you can change the effective lift of the valve due to the angle the rocker makes with the valve stem. Remember the rocker tip moves in an arc.

Nice!!:ernaehrung004:

Well I pulled off the valve covers to rejust valves, doing some measuring, and checking things over. As far as the valve stem and the witness marks from the roller rockers the circular pattern seems to be pretty close to the center of the valve stem, which I think is a good thing. Now as far as the lift of the intake valves I am supposed to have .54226 lift with the 1.7 rocker ratio. I very carefully tightened up the adjuster nut until the lifter was actually bottomed out so it was just to the point to were the rocker was going to start opening the actually valve, I did this so I wouldn't have any oil bleed off in the lifters. I then put the travel indicator on the valve spring retainer and rolled the motor over by hand to see what I actually have for lift. Now I am using 1.72 roller rockers so the lift should be a little higher then the .54226 and the indicator actually read .5483. I did this on 4 different intake valves and got the same reading within .0003. So to answer my own question longer push rods will not change the amount of lift you have. So now by running push rods that are just under .100 long will that change the geometry of the valve train and or effect the performance of the engine?

The reason I am doing this is because the boat does not have any top end, it seems to be pretty flat from 2/3's throttle to wide open throttle. My boat would run right at 67 mph with the old engine with two cam lobes starting to go flat and the compression being 90, 90, 110,110, 120 120, 110, and 120. The engine had 504 hours on it. Now with the new engine and the camshaft change and the ecu reprogrammed the motor was designed to be at 485 to 490 hp and the boat doesn't run any faster at all. When we put the scanner on the motor the knock sensor was retarding the timing .982 degs at 3000 rpm. We readjusted the valves and that seems to take a lot of the problem away, but it is still retarding the timing .34 degs at 3000rpm. When we unplugged the sensor the scanner was picking up any timing retardation! Could the longer push rods be causing a little noise or a knock in the engine and the sensor is picking it up?!?! I am at a lose here, this motor should run better then this and I am running out of things to change or try. The only other thing I am wondering about is the fuel pressures could I be running a little low on fuel pressure causing the engine to ping and the sensor picking that up? I did change the filter and there was no change to the way the engine run.

Just so you all know the timing was set at 8 degs in the service mode too.

Please help

It depends...have you changed the prop??? What RPM is peak tq/HP? How much more HP did you make?

Just because this engine makes more HP doesn't mean it will go faster with the same prop. How much more torque did you make and where does the torque peak compared to the old engine? You may actually have to go down in pitch on the prop to get the RPMS up to where you're making peak HP and the might run faster.

Not saying this is the answer but I've seen it happen.

Lastly, what is your timing advancing to @ full advance? How was the ECU mapped?

I started off using the same prop I used with the last motor and could only spin it 4600rpm which is the same rpm the old motor would turn it. I am supposed to be making 485 to 490 hp with new motor and the old new was 415 in good running condition and the motor had over 500 hrs on it. As far as torque goes I can not answer where the peak torque is at as far as rpm wise. Mark at Precision Marine did the ECU for the cam I am using, I could call and get that info. Logic is telling me if I am making more hp with the new motor and by stay with the same prop I ran with the old motor I am going to be able to turn that prop more rpm and more then likely have to go with a higher pitch prop. The motor just seems to be laying down on the big end for some reason and need to figure out way it is doing that.

think I found the problem. I am supposed to be holding 40 lbs of fuel pressure and at half throttle the pressure is at 35 and at full throttle the pressure falls below 30lbs! Now what pump do I change or do I first remove the check valve in the tank and see if there is a restriction! I was told the fuel system on the motor from factory will support up to 650 hp so I don't feel I need a high volume pump or do I?!

Thanks