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1975 Johnson 40EL starting issue

T

tgsail

New member
I bought an old boat which came with a seized Johnson 40. I pulled the cylinder head and sprayed penetrating oil on the rather rusted pistons. Used a block of wood and hammer to free the pistons and got it to turn over. Replaced the head, cranked it and it started right up and ran it for several minutes. Did a little more maintenance (carb float, reed valve) and put it to bed for a while (with oil in the cylinders) . Went to try it again, rotated the flywheel to make sure it turned, had obvious compression. Removed plugs sprayed oil, rotated the flywheel and it moved freely. Replaced plugs, went to start and the starter struggled to turn it. Battery new. Replaced the starter (non-trivial on the 1975). Tried again, new starter, same problem- struggled to turn over. Bypassed relay using a jumper cable- same problem. Pulled one plug, and it started right up. Swapped plug to the other cylinder and it struggled to turn over. Obviously one cylinder has much more compression than the other, but so much it interferes with cranking. I went back to the original reed valve and it made no difference. I wouldn't imagine that too much compression on one cylinder would be a problem. Has anyone experienced this? Thanks
Todd
 
Might be a bad bearing inside on the crankshaft.-----Reed valves have nothing to do with compression in the cylinders.
 
Thanks. It cranks fine without compression and with one cylinder compressed, but not the other. That seems to rule out bearings unless the bearing in question is only jamming under compressive load (which is possible). Is there some obvious way to tell? I suppose I can go back and do a compression test and see whether the extra load is due to compression or bearing binding.
 
Somewhat surprising compression result. The upper cylinder, which turns over easily and starts, measures 30 psi (very low). The lower cylinder which has difficulty cranking measures 90 psi. Not sure what to make of that.
 
Head gasket was replaced with the head. Might be a combination of bearings (no cranking) and rings or cylinder scoring (low compression on top cylinder).
 
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