I've got an '88 F-150 4x4 that started life with a 4.9 6 cyl. When the time came for an engine change, I opted for an EFI 5.0. I got the entire engine and harness from a wreck. When I rebuilt the engine, I bolted on a set of fresh '69 351W heads with the larger valves. I used the Ford Motorsport head bolts for this swap with '69 302 pushrods. The logic here was to have the correct pushrod length and ball to mate with the iron stud-mounted rockers that went with the heads. I also used a mild Ford Motorsport cam (I can't remember the grind of the top of my head) and did a mass air conversion too. I got it running and for the most part was satisfied with the performance, but I always had a slight "stutter" at cruising speed. I went over the whole EFI setup and could find nothing wrong. 8,000 miles later, I burnt an exhaust valve. I'm getting ready to tear into it to fix the valve and I've been asking around about why this may have happened. I've NEVER burnt a valve before. The guy at the local speed shop says that 351W heads on a 302 require an ever so slightly shorter pushrod. He says that slight differences in valve stem lengths and rocker/lifter machining may not give you enough clearance on some valves and not allow them to close fully. He claims this was the cause of my mysterious stutter and the burnt valve. Anybody else have any thoughts on this? Anybody ever do this head swap before? I'd like to know if and where I goofed before I peel the lid off and start the repairs. Help!

Peace, brothers.

 

[updated:LAST EDITED ON 10-Nov-01 AT 03:24 PM (EST)]That is a problem with fords anytime you do any serious modifications. The problem is the non-adjustable valvetrain. Why don't you call summit racing, and see if they have a kit, where you could convert your rocker arms to adjustable ones. If you have the rail rockers with studs in the heads, they make a kit with a long nut and an allen head set screw that fits down in the middle to lock it when you have it adjusted. If you have the rockers with the bolts, they have a kit that changes it over to a stud with a plastic coated pushrod guide plate. Then I think they give you a locking nut that is adjustable to hold the rocker arm on. Summit has a footnote on all their cam kits that these adjustable valvetrain kits may be required with their cams.

 

The '69 Windsor heads DO have adjustable rockers. I have an '80 302
with '87 Windsor heads (non-adjustable) and have had no problems
after 20 + thousand miles

RCC

 

sounds to me like maybe the valve job wasn't done correctly or you may be running a little to lean ? just a thought , never heard of running a shorter pushrod on exhaust