Sticking valve in a rebuilt motor

[John-T-53]

On 3/12/2019 at 5:09 AM, 41/53dodges said:

Good morning guys, been forever since I posted a new topic but this one's got me stumped. Last winter I built up a 265 Spitfire engine for my B4b, used an edgy cam, shaved head, and heavy truck manifolds for now. Ran like a Swiss watch. I parked it in fall just before the snow started but usually light it up every month or so. I've noticed that when I start it, #1 exhaust valve keeps hanging open, usually it will come free on it's own accord once it warms up but this time no dice. Had to pry it back down with a screwdriver, and it stuck again immediately. Even tried running it and being the valve spring. Darn thing just sticks up, and makes it sound like a messed up Harley! Has anyone seen something like this before? 

 

Josh

 

What are the guide to stem clearances that were set? I believe that the spec calls for a pretty tight clearance (.001 - .002" or so if I remember correctly - just guessin') and the exhaust is a tad looser than the intake. This leaves little room for slippage if any foreign material, gum, or varnish gets in there. I'd try applying some extra lubricant as others have said. If it still gives you trouble you might have to remove the head and valve and 'kiss it' with a guide hone.

I too had a sticking valve after doing a valve job a few years ago - on the way to the BBQ actually. it happened on the side of the freeway. Luckily it popped back with a screwdriver and didn't stick again, and I was back on my way shortly. The culprit was a speck of metal or something - it scratched the stem.

[41/53dodges]

Fantabulous question, let me clarify. This block was out of a 47' dump truck, PO bought it as a remanned 237, put it to work for a few years and parked it back in the 80s. Buddy bought the truck and yanked the motor with big dreams, I stripped it down, cleaned up all the rust, honed all the cylinders, ground all the valve seats. New bearings all around, 265 crank, .060 Pistons, new valves to replace the broken ones, and an edgy 1/4 cam. 

In short, I didn't clearance the valve stems myself. I made sure they were good and tight. But I'm subscribing to the rust theory, some marvel probably ought to do the trick, especially since it hasn't been up to operating temp since fall

[kencombs]

With that background info, truck ran with those valves in those guides 'for a few years', I think it's safe to conclude that clearance is not the issue.

[Dodgeb4ya]

 the guides need to be  free of debris /corrosion before inserting the valve guide pilots using a valve guide brush.

On a relatively new guide a .342" pilot should fit snug fully pushed down.... with corrosion in the guide I doubt that pilot would barely go down into the guide... a sign of dirt etc.

.002" to .004" Exh. guide clearance.

[John-T-53]

Were the tappet covers removed? If so, any corrosion or varnish may be evident on the valve stems in the closed position. If considerable corrosion is evident, it should also be present on the other interior surfaces of the motor. Take some photos of the tappet chamber and post them here.

[41/53dodges]

1st thing I checked, that would be awful to find. But nope, all clean inside. Went to do battle and hose it down with marvel the other day and the darn thing wouldn't stick! So I hosed em all down anyway and let it run awhile. 

[Jeff Balazs]

IMO these engines were built in a time and in such a way that build up or deposits of carbon, varnish etc are going to happen. Particularly around the valves. It is kind of the Achilles heel of these old engines. To my way of thinking the best way to keep this in check is to run a good detergent oil and use something like MMO in the fuel. MMO definitely has some ability to dissolve varnish etc. I know that there are many who will disagree about using a detergent oil....but I say they are worried about things which are not really likely to happen. I think it is actually critical to maintain a clean supply of oil and fuel to the valves on these engines. Running a modern detergent oil is the best way to insure this is the case. Beyond that you can help things a bit by using a fuel additive designed to keep things clean.

This is my take on this based on my experience driving one of these trucks every day for about 4 years.

Jeff