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Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
Alright what do you guys think? Got back from a good ride and saw what looked like oil splattered on the front of the head. Engine was newly rebuilt (about 350 miles in since building up) and since it seemed concentrated around the head gasket so initial thought was blown head gasket. Took out the plugs and did a compression test, 120psi on the front, 100 psi on the back cylinder....hhhhhmmmmm......started to tear down the front cylinder and when I went to remove the exhaust manifold, the bolts felt pretty loose...looking at the "dispersion pattern" now I'm thinking maybe it was just an exhaust leak? Which if it was, it seems a little too fluid for exhaust. Maybe from running too rich? I think ill pull the head off anyways just to be safe and took a look at things. '92 Sportster with 88" upgrade and stage 3 heads. Pics below: Front Head Front Head Exhaust Front Head Front Plug and Rear Plug
[QUOTE=pleasants9;21221978]Alright what do you guys think?
Engine was newly rebuilt (about 350 miles in since building up)
Took out the plugs and did a compression test, 120psi on the front, 100 psi on the back cylinder....hhhhhmmmmm......
Numbers are low. Did you hold the throttle wide open and lift the slide up (if applicable) when checking compression? Oil in the front cylinder could cause the higher compression. Was the front cylinder smoking?
It definitely could be from an exhaust leak and not headgasket.. From the looks of things, I'd suspect a leaky exhaust valve seal.. While the front plug is rich, it's not oily. Pull the pipe and look at the exhaust valve. You'll probably see oil running down the valve stem.
*I may have done the compression test wrong as I did not open the throttle*
Attached are photos of the exhuast manifold and valve. Not as much fluid in the front manifold as I would have though but does look like there may be a leak at the valve? Front Exhaust manifold rear exhaust manifold Front exhaust valve front exhuast valve rear exhaust valve
Well, I don't see any oil running down the guide. It's pretty dry. There appears to be way too much carbon for a motor with only 350 miles tho. I would expect the exhaust port to be not as white as it appears.. Motor running hot. Has it been tuned? I'd guess it could be leaking past the rings or the intake seal but the motor is running hot enough to dry out the plug..
Add:
Even with a high perf motor, with intake seal leaks, I've seen a little oil on the plug threads.
Last edited by Max Headflow; May 22, 2023 at 11:51 AM.
Reason: add
In the 3rd pic you can see oil to the right of the valve, where is that coming from? Agree with Max, waaaay to much junk in that exhaust port for 350 miles
In the 3rd pic you can see oil to the right of the valve, where is that coming from? Agree with Max, waaaay to much junk in that exhaust port for 350 miles
In the third pic I see some possible wetness on the side of the port but none on the valve stem.. I've seen it running down the stem before.
At 350, I'd expect the motor to be using some oil. I certainly hope this motor doesn't have the breather routed to the intake.. Probably worth springing for one of those cheap cameras that can slip into the plug hole and maybe the intake port..
In the third pic I see some possible wetness on the side of the port but none on the valve stem.. I've seen it running down the stem before.
At 350, I'd expect the motor to be using some oil. I certainly hope this motor doesn't have the breather routed to the intake.. Probably worth springing for one of those cheap cameras that can slip into the plug hole and maybe the intake port..
Yup no oil on the stem. Possibly coming from the cylinder and being pushed past the exhaust valve? One would think it'd be puffing smoke pretty good. Was it down on oil?
Took the front head off just to be thorough and no sign of anything suspicious, the seal didn't look like anything had blown through. When I rebuilt the motor I tried to tune it myself but I'm starting to think I did not do a sufficient job. there was a little bit of fluid sitting in the port of the intake valve when I pulled off the intake manifold. I think I have two issues.
1) The front exhaust manifold was loose which caused the leak
2) Bad Tune, I think the motor has been running super rich which has resulted in excess carbon and unburned fuel.
Pics of the valve and piston (The scratches on the piston are from me, dropped a small washer down the spark plug hole and had to fish it out with a screwdriver I magnetized..)
front head underside Front piston at TDC
I think I'm gonna put it all back together, verify torques then take it to a shop to tune since I did a bad job. Maybe also lean out the Mikuni carb?
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