I've recently had my 351m rebuilt and now am having a problem with some of the "hardened" Comp Cams pushrods mushrooming under the FMS Roller Rockers. This is the second one in as many weeks to do this. Tonights pushrod happened to be the farthest one back on the passenger side and wouldn't you know it, you can't just pull it out because it hits the A/C box under the hood! But that thread is posted in the 73-79 forum.

What I'm looking for here are possible reasons for these pushrods to mushroom like they are.

Motor specs:

Block "zero-decked" with .060 over replacement pistons (13cc dish)
Aussie Cleveland heads with new valves, hardened seats
Comp Cams Xtreme Energy 256H (XE256H-10)
Double Roller timing chain set straight up
Ford Racing roller rockers
Comp Cam springs, retainers, locks, lifters and pushrods
Edelbrock Performer 400 intake
Proform Electronic Distributor (uses Duraspark brainbox)
8mm Ford Racing wires, factory coil and harness
Holley 600 Electric Choke vacuum secondaries
Crank turned, rods recoditioned and new ARP bolts for the bottom end
New Damper from Summit
Total reciprocating assemble balanced.

Timing is set to 14 BTDC, 36 total. Rnning 93 octane and no pinging.

Engine is feeling like it is just not all there. Under load at 30-40 mph, if I mash the loud pedal it wil backfire. Under normal to moderate takeoff, seems to have decent torque. (I'm guessing on a lean-out condition) Idles smooth and does not diesel when shut off (at least when the pushrods aren't mushroomed and all the valves are.. well.. valving correctly)

Ok guys and gals, let the questions begin. I want to solve this problem before it snows so I can keep the Mercury Marauder in the garage all winter.

John

 

Sounds like you need to measure your pushrod length and check your valvetrain geometry etc.

 

It could ba a lot of things: retainer hitting top of valve guide at full lift, rocker arm hitting stud at full lift, coil bind, valves hitting pistons, not enough clearance between spring and rocker, not enough clearance between stud and bottom of rocker, not enough clearance in guide plates, push rods hitting rocker, not enough valve guide clearance. I would recheck valve train geometry first and make sure you have the right length push rods. I don't think this will be hard to figure out, you will just have to be thorough in your investigation.

 

edit:

nevermind, missed some info related to my post. disregard.

 

Just got off the phone with the Comp Cams support line. After a full detail of the enging and the installed parts, they came to the conclusion that the pushrod seats of the Ford Racing roller rockers were harder than the tips of their 7837-16 pushrods that I purchased.

Basically, these are a 3-piece design with the little ball welded on each end. He also mentioned that this was the lowest on the end of durable that they made. They had me move up to the 7656-16 ($102 at Summit) which is a one-piece hardened pushrod that is 5/16 with a rounded tip and not a ball that is welded on. Strongest ones they made.

Apparently this isn't the first time they have heard of the mushrooming tips with the Ford roller rockers.

Thanks for the input everyone. Summit says about 2 weeks till I see them and after I swap them all out I will keep everyone posted as to my success or lack thereof with them.

Cheers

John

 

That is a very strange explanation. There should not be a problem with the strength unless you are running into spring bind etc that was mentioned b4. I would suspect your zero decked block has your valvetrain geometry compromised. With the new high strength pushrods something else will break. In the meantime you are putting tremendous loads on your cam. Unless you find the source of the extreme loads on your valvetrain the prognosis for your engine is a very short life.

 

Strange as it may sound Torque, these guys are the experts. There is no coil bind or excessive loads on the valvetrain. I'm running 940 springs which have less load than the 972 that the cam card specified. I told that to the Comp Cams tech and he said that was not the source of the problem. Remember, I had a bigger cam in this motor when first fired and there was no bind then.

Valves aren't hitting pistons, the rocker tip is rolling across the valve stem correctly. I will reset the shims when I adjust the preload on the lifters with the new pushrods.

Unless the occasional backfire is jamming the valve back up and wrecking pushrods, I will take their advice and put better pushrods in. I didn't pull a mic out (will do that today) but I wonder if the cup on the roller rocker isn't just slightly different than the ball tip of the pushrods.

However, I did learn something new from them yesterday. Comp Cams grinds their Magnum and Energy cams 4 degrees advanced. To get true 'straight up' timing on them, you would have to use a crank gear set 4 degrees retarded. With the higher compression of the aussie heads, I wonder if I should pull the timing set off and reset the crank gear to 4 degrees retarded to get a lower static compression number? Anyone with DD, can you check this for me?

John

 

You will never know for sure unless you degree the cam in, too many variables.

 

Good luck with your engine.

 

With the Comp Cams XE256 installed 'straight up' the IVC is 54 degrees ABDC. The DCR is 8.7:1. That is definitly in the detonation range. The cam is ground advanced 4 degrees, so retarding it 4 degrees sets the valve centers at 110 degrrees instead of 106 for intake and 114 for exhaust. Now the IVC is 58 degrees ABDC and the DCR drops to 8.49:1.
I am suprised that you don't get detonation even with quench, but it will have no effect on your pushrods.
Your backfire could be due to a blown power valve on the Holley carb.

 

Thanks for the DD Dan! I am sure I have carburation issues with this Holley. Not that it is a bad carb, but out of the box it is not tuned to my engine, I'm sure of that.

As for detonation, if I have too much advance I can get it to detonate no problem. With it set for 14 BTDC I'm having good success. (sans the pushrod issue that I will have cured shortly)

I've decided to put the factory rockers back on while waiting for the new pushrods to confirm that the problem is indeed mixing those three-piece pushrods with the Ford roller rockers. Can't hurt and I'll still be able to drive it while waiting.

While I have your ear (<eyes>), how much does decking the block and going .060 on the bore affect the different DCR figures? Is there a sort of "rule of thumb" to go by? I don't have my machining papers here so I don't know exactly how much was taking off the block when it was zero-decked, but there was some.

Cheers!

john

 

A stock 351M with 59cc combustion chamber and 13cc dish on the piston and 0.016" deck clearance will have a Static Compression ratio of 9.6:1. With a cam that has an IVC of 54 degrees ABDC the Dynamic Compression ratio will be 8.2:1.

Now if I bore it +0.060 and zero deck the block the SCR is is 10.2:1, and the DCR is 8.7:1.

So boring +0.060 and zero decking the block adds about 0.5 to the SCR and DCR, since it affects both equally.