The Stovebolt Site Forums The Shop Area Engine Shop bent valve

running great all new rebuild on a 1956 235 in a 1952 1.5 ton dump. 1st time running with a full cooling system and at a idle bang starts poping though the carb with a mis.Great oil pressure had good piston to valve clearance at time of assembly. found #2 intake valve bent with piston contact and a slight contact on #1 intake but not enough to bend. all the other intakes were just fine could the valves have seized in the guide from a full heat to 180deg. the other runs (about 3 hours) were on a hose in the front and bleed out the back. any ideas ?

Was the head reconditioned by a machine shop? It sounds like the valve stem-to-guide clearance was set up a little too tight. When the engine came up to normal temp, the stem expanded a little and seized in the guide. I'd reccomend checking the guide inside diameter with a ball gauge, and compare it to the valve stem diameter. Too little clearance is far worse than a bit too much.
Jerry

While the head is off, I would take a small hole gauge and measure all the guides and compare them to the stems. Did you guy new after market valves. I have heard of quite a few of the off shore valve stems expanding more then the OEM did and will seize when they get operating temperature. Also, how old was your gas? Stale gas will cause valves to hang open.

the machine shop said the guides were to tight when they did the valve job. I had all new valves and hardend seats put in when I did the rebuild I will now find out about the offshore valves though.thanks for the heads up on that. I never use cheap parts when given a choice and I was not given that choice.

Sounds like your on the right track with the valve guides. We had a John Deere 40 do the same thing after a guide siezed.That one took out the piston and did major damage to the head. Sorry to hear about your bad luck but it could have been worse.

Is the shop going to correct their mistake at no cost to you? They should at least ream the guides for the correct fit and give you a new gasket set, and if possible, compensate you for part, if not all of your labor time.
Jerry

I would have reservations about going back to a machine shop who assembled a head knowing there was not enough clearance. All it takes is a small hole gauge and a mike to tell in a minute if there is enough clearance. No telling what they will screw up next time.

your right. Normaly I catch these types of problems (block ,crank,rods,) but it has been a long time since I double checked a shops valve work. once the seals are installed I normaly do not take back apart the heads. makes you think.

I do my own valve work, but it's not up to the customer to take valves out to go behind a machinist. Most of their customers probably don't have the capabilities of removing valves and measuring the guides and stems. The next thing is, did they center the seats and how wide are they? I would think that is why you went to a machinist in the first place to make sure it was done professionally.

yes this shop has always been right on for me. I think the import valves are what got us I always get high end severe duty style. this time I just did not ask and there parts guy received cheap imports live and learn.