Quote:
Originally Posted by Tony Wheeler
Yes I was suggesting there's no immediate problem Malcolm. You seem hell bent on removing the heads prematurely.
Actually I'd hoped to save you the trouble by pointing out that the motor is ALREADY running well. That's impossible with stuck valves. Perhaps I should have elaborated as it can be difficult to visualize:
The so called "stuck valve" or "sticky valve" syndrome common to flatheads is caused by corrosion of exposed valve stem on open or partially open valves during long standing - the result being a snug fit in the guide which cannot be overcome by the puny valve spring. Hence while the valve will OPEN fully and freely, it will stop on the way down when the band of rust on the stem hits the guide. Symptoms are ZERO compression, and if it's an intake valve, some audible blowback through the carby when cranking over. Such a motor will definitely not run! The solution as Rob describes is to "tap it down, crank the engine, tap it down again, crank the engine...." Generally after several repetitions accompanied by ample lubrication of the valve stem it will require only a single light tap, whereupon the valve will snap shut under valve spring pressure with a satisfying "plop". Thereafter a few more repetitions will generally see the valve no longer sticking at all.
The point being that stuck valves, once unstuck, cannot become restuck! Once they're dislodged and start moving again the corrosion quickly rubs off and the valve will seat normally - particularly once the motor starts running. The idea that valves might stick partially open is a mechanical impossibility. For example, consider a motor running at 3000 rpm, with the valves hammering up and down 25 times per second. No collar of rust on the valve stem can persist under those conditions.
re: I added oil to #7 and no change, still 30psi. So not rings, at least for that cylinder. I'm thinking, pull the intake manifold and heads and check bores, valves, guides, seats, head gaskets.
You're certainly itching to pull those heads off Malcolm! Can I suggest you restrain yourself long enough to perform wet and dry comp test on ALL FOUR deficient pots. That way you'll be in a position to confirm your "not rings" diagnosis.
re: This carrier is in very nice, restored condition and the engine was supposed to have been rebuilt. Looks like it wasn't.
I'm probably clutching at straws here, but it's just possible the motor WAS rebuilt and the valve clearances were insufficient. It's not unheard of and it can lead to valves not sealing perfectly after running in, because the clearance is further reduced as the new valves and newly ground seats bed in. This would be consistent with compression readings: 90-95 psi indicating rebuilt motor; 30-50 psi indicating zero valve clearance on those pots. It would also explain: "Oil rings are good. No smoke, and no carbon on plugs or valve/head visible through plug hole." That does not sound like a tired old flathead with burnt valves.
In any case the heads should not be removed until this possibility can be excluded. That means removing the intake manifold and checking valve clearances. Yes it may be wishful thinking but you never know your luck sometimes!
|
Your post and its annoyed tone puzzle me, Tony. You say the motor is running well, yet it has 2 cylinders with 30 psi compression. Yes, it starts and drives, but it is not a well-running motor IMO.
I didn't think for a minute that valves stuck open because of long storage was the issue here, for the reasons you explain in such detail, but I suspected the springs on these engines were fairly light, so maybe varnish build-up on the stems or carbon on the seats preventing some valves coming down tight? A long shot, but the tapping the valves idea was suggested and it was easy to do, so why not?
So as a newbie to these engines, with the heads so temptingly accessible, it seemed a simple job to pull both the heads and intake manifold and check for ALL the various top-end related issues that could be causing this, AND fix them in the time we had available. All in one fell swoop.
Of course, now I know it isn't that simple to pull the heads, nor is it that simple to do a valve job on these engines, so we'll just run the old girl as-is until there's a space in her schedule to do the work.
Malcolm