Cylinder heat
Cylinder heat
After a good hard ride with my Wife on the back on our 1982 FXRS Shovel I went to wipe the bugs off with a wet rag. When I touched the rocker boxes the back one was still hot enough enough to evaporate the water quickly but the on the front one the water boiled and sizzled, obviously much hotter. I was under the impression it was the back cylinder that would run hotter for good reasons but on our bike it's the front. I've looked for intake leaks and I don't think there are any but when I've run the bike on just one cylinder (pulling a plug) the front one seemed stronger than the back by a little. The compression is the same for both. There is an oil cooler and I can usually put my hand on the oil bag without burning. Could there be more oil cooling the back cylinder than the front?
Road Warrior
Joined: Dec 2007
Posts: 1,286
Likes: 64
From: SoCal
Many years ago when I got into HD's, I thought the same as you but a very competent HD mechanic/machinist told me that the front cylinder does, in fact, normally run hotter than the rear. The amount of difference between the two cylinders and the reason(s) for it are long forgotten by me. But I bet someone on here knows.
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
Likes: 5,449
From: la la land jerzey
it has to do with the oil volume not as much in the front as the rear because of the cylinder angle -- the round flywheels spitting off oil the rear is directly in the line of site the front only the bottom of the exhaust side - think about it --
if its running fine and the plugs are not white than the intake is still sealled - if not replace the rubber bands on the intake / head -
if its running fine and the plugs are not white than the intake is still sealled - if not replace the rubber bands on the intake / head -
Thanks
I thought it might be oil but also the properties of air might be adding to the problem. In aircraft and old VWs the cylinders are tightly wrapped so a limited amount of air has to pass over the fins. Air moving too fast doesn't cool well. The front cylinder could be experiencing that since it is more directly in the air blast where the aft cylinder is in more turbulent air. I've toyed with the idea taking some of what I learned setting up the baffling on my experimental airplane and doing some sort of baffle work to get the air more rapped around the cylinders. Has anyone ever tried this? Another question, the aft spark plug gets fouled on one side only, the rest of it looks pretty normal. It looks like cooked oil to me. It seems to run OK I just swap the plugs sometimes and it burns off in the front cylinder. Could it be coming from a valve guide?
Seasoned HDF Member
Joined: Nov 2006
Posts: 12,878
Likes: 5,449
From: la la land jerzey
guides leak in two places one is the seals wiper goes away and no longer removes all the liquid oil - film if fine not liquid - and or the valve to guide clearance is worn out
second place is on the out side of the guide from an incorrect press fit of the guide to the head and oil seaps around the guide fit to the cylinder head - this type usually causes on throttle smoak
second place is on the out side of the guide from an incorrect press fit of the guide to the head and oil seaps around the guide fit to the cylinder head - this type usually causes on throttle smoak
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