victory32

Some advice please, Have a pair of 502mpi motors with 70 hrs, was in a poker run and lost power in one motor,It has a miss in it, pulled plugs and all are black and look alike, number 2 has 0, and I mean 0 compression, the rest are at 125, whats the next step, pull valve cover(valve stuck open) or piston prob and pull the motor? Thanks in advance

victory32

Did a test and #2 exh valve blows by, push rod bent, motor made no abnormal sounds when running but had the big miss, I guess pull the head right?, rockers were tight , valve didnt drop, why the bent push tube ??Should I pull both heads?

CESSNA

I'd pull the intake and check the rollers then valve springs I heard their bad

victory32

Good advice, I'm running twins so I'm thinkin if I more than one bad spring is found maybe I should pull the heads on the second motor also, so heres my next ?, If no piston damage is present should I recam and put a new set of alum heads on(dart, brodix) and what makes the most hp?!. I've heard the 502 has had a long life 400 to700 hrs, but I run WOT alot cuz thats when it's fun.
Always wanted to whipple or pro charge these but didnt have the $ for drives to complete the package.

victory32

Just got done pulling off the heads, only one bad push tube and one bent exhaust valve, whats the most economical way to fix, have both heads cleaned up, replace just the bad valve and push tube, replace the lifters???, Trying to get this done for next weekend ! I know I should use felpro gaskets any other tricks I need to know ?, The pistons have some carbon build up, what do you clean them up with ??? Brass wire wheel?

Griff

Something caused the valve to hit the piston. You need to find out the cause so it doesn't happen again.

The valve and pushrod are bent because the valve hit the piston. How's the spring on that valve???? How is the valve guide???? You need to figure out what happend FIRST and make sure the root cause of the problem gets fixed.

victory32

yes it did hit the piston, , put a small grove that a friend said smooth it out and no worries, trying to get references on a local machine shop that can help asap, face of the valve is ok.
Will the inconel valves come with springs, whats the best to get if not, I would assume to change the intake springs also.
The cylinders look good , can see the hone marks from the factory. Thanks formulafastech and griff for your help!
This is the first eng prob I have had , all the previous boats ran without a hiccup and weren't stock for at least 150-200 hrs, maybe lucky I guess.

bobby daniels

If it was my motor I would put springs on it anyway since the heads are off and put a 731 or 741 crane cam in and at least one lifter on the bent push rod cylinder ,Fasttech told you straight !!!
fel-pro gasket and don't please loosen the stuff on top of piston as it will get in ring lands maybe and thats bad !!!
But as Griff said you have to find the problem first most likly an inner spring or detonation ?? what did the spark plugs show lean ??? spark knock ??

victory32

This is what I got, 3 exh valves were starting to transfer metal, all springs tested perfect, the 1 valve looks like it got hot and stuck, re did the heads , replaced valves,( no inconell avail in a 1.88)put in spiral valve guides and opened the clearances for better oiling. The motor was running fat, the plugs were black, anyone here of the 502 with poor oiling in the valve guide?
As far as cam goes Bobby, the other motor seems good so that will be a winter project because I want to get back in the water asap!
Now for some help, I don't have the specs on the 502, anyone with specs on what to torque the new heads and rockers to, it's been awhile so how is the timing set up? Alot to ask I know but any advice is appreciated !!!

Tinkerer

When you say spiral valve guide do you mean that they put a spiral groove in YOUR stock guides? If this is the case have someone bronze wall the guides it is a lot better and you probably won't stick a valve from lack of oiling again.