Aft most valve stuck

[Sculldog1]

Hi all. Just had to unstick the last valve (cylinder 4) closest to coil end of engine. The trouble was that 3 and 4 cylinders were not firing. After compression test found 1, 2 and 3 with 70 or so psi each and 0 on number 4 I removed valve cover plate and was able to free the stuck valve. After turning the engine over for a while and soaking the valve in mmo with squirter and filling adding some through plug hole it seems to be back to normal.

Question: how come number 3 compression was same as 1 and 2 yet that cylinder would not fire?

[Mo]

How do you know it didn't fire? If you had spark on all 4 cylinders the spark plug on all 4 "should" have fired. I'm not sure I get your meaning. Bad plugs and or wires could contribute to issues with hard or no starting. How's fuel delivery. Once you freed up that valve on number 4 did you do another compression check?

Anyway, I would pull the plugs one by one and attach the wire turning it over watching for spark on that particular plug...might as well do them all. You could check compression again...70 is moving down on the spectrum in my view, however a table spoon of MMI down each spark plug hole as you do that check should increase your compression a bit. Might be rings sticking as well, a little bit, bringing compression into the 70's. A drop if oil might get it to come up a bit and if she has spark fuel and air she'll go.

Also ensure you firing order is correct...when we have trouble it's easy to switch a wire and complicate things...check it over. Often a couple of small things come together to give us a no start.

During winter lay up I put oil in the top end at season end then turn the engine over about once a month...every month. No valve issues.

That's what I'd try first. Just take your time and go through everything.

Hope that helps.

[Sculldog1]

Thanks for the good advice Mo. I guess I may not have been clear in my description. I always had spark in both 3 and four but the last valve being stuck open created the 0 compression in number 4 when I tested for compression. The original condition of running on only 2 cylinders led me to the stuck valve diagnosis. I just wondered why stuck a exhaust valve on 4 (that is the very last valve in the gallery being exhaust for cylinder 4? If I am correct) might cause cylinder 3 not to combust, if you will, in spite of the plug sparking and having compression on 3 when tested. When first having the poor running I found both 3 and 4plugs were wet with fuel but felt cool to touch and clearly had not been combusting. Having freed up the stuck valve and restored compression to 4 back to similar as the other 3 would you say it is safe to reassemble and run the engine? Prior to the running on only 2 cylinders the engine had been running great. I did a valve job last year, removing, cleaning, lappjng, and actually replaced the last two valves (including the stuck one) and set the gaps to the specs from the MM Manual. I will check them again before reassembling to be sure. Any thoughts appreciated. Thanks again

[Dave Neptune]

Double check to be sure the plug wires are in the correct order. It is easy to get them mixed up.

Dave Neptune

[Mo]

Yes, if your valves are all free now by all means reassemble everything and see what you have. The number 3 and 4 should not have been related. As Dave noted, check your firing order, take a second to find NO. 1 on the distributor and 1,2, 4, 3, for the order.

[Sculldog1]

Thanks for the feed back guys. I sure will double check the firing order and plug wiring upon reassembly. Got a new cap, rotor and wires to go on also so hoping the sticky valve was all that was wrong.

[Mo]

If it still doesn't seem right do another compression check on 3 and 4 just to ensure you have decent compression and no head gasket failure between cylinders. I think it a fire issue though....you'll find out soon enough. Don't overlook the plugs either. I once chased a miss and it was only where unburnt fuel was on the water near the exhaust outlet that I noticed a gasoline sheen...Id overlooked checking the plug and sure enough.

All the best