Hi guys, I Just recently completed a 95" build on my 2002 fatboy. Was running well for the first 20 mile break in ride except for a little dark smoke out the rear cylinder exhaust. Ran smoothly and pulled hard. I assumed it was an air / fuel / leak issue. I did a compression test and got 180psi front and 190psi rear. So I thought all was ok.

Today I fired it up the bike to check for intake manifold leaks and then a LOT of GREY smoke started coming out the rear cylinder exhaust....

Shut it down and then checked the oil. It was very very frothy, and murky dark brown in color. This was fresh oil I put in yesterday.

Could I've done the head gasket? There are no signs of damage / leaking around the base of the heads or top of the cylinder fins??
Retested the rear cylinder compression and it's still bang on 180psi....
Thanks for any advice.
I've never done a head gasket before on a bike or a car....

 

If you checked the oil right shortly after the bike was running, those bubbles are normal. All my
HDs do the same.

Some amount of oil remains in the sump etc during an oil change, more so if/when an oil change is done without warming the motor up first. That mixes in to the fresh oil and can make it appear slightly darker. Also, the inside of the oil tank being a dark place inheritantly makes the oil appear darker than it is.

I’ve dealt with slightly leaky head gaskets on a couple occasions and I couldn’t tell by the oil. These motors also exhibited spot on compression readings and did not smoke.

A leakdown test would also be helpful, that will help pin point a ring issue, head gasket issue, etc. I’d pay close attention to the smoke next time and see if there’s a bluish tint to that grey. If so a ring, guide, guide seal issue is likely.

 

Thanks Matt, that's reassuring. I've looked very closely at the cylinder fins where the heads meet the cylinders and can't see anything obvious....

What's a leak down test?

Thanks

 

Sorry bother, just edited my post some to include more after you quoted it.

A leakdown test introduces air into the cylinders and measures the leakdown percentage / how much air is leaking out. A high percentage on a particular cylinder will point to air leaking past the rings, valves, etc. It’s a good diagnostic tool to have around. A little more involved than a compression test but not terrible. Here’s the unit I have for example:
https://www.amazon.com/OTC-5609-Cylinder-Leakage-Tester/dp/B0030EVL60

Does the smoke look similar in color to this? This is when I had a ring issue, would do this on cold starts:

 

I forgot to add…if you used any engine assembly lube during assembly, some of that stuff can make the oil look FUNKY. Depending on the lube contents, can make the oil look metallic like.

 

Thanks Matt, yes that's what my smoke looked like.
I just thought that if my compression is still good - 180psi - how can I have ring problem ??

What was wrong with your rings and how did you fix it?
Cheers

 

UPDATE:
Took the bike out for a good hour long run. These are the ONLY symptoms I'm getting.

1. Bike starts easy, runs well. No apparent looks of power.
Rear cyl has dropped from 190 to 175psi on latest compression test

2. I'm still getting quite a bit of light grey smoke out the rear cylinder exhaust.

3. Pulling the rear plug after a run, it's still black, almost a shiny sticky residue.

4. Front plug looks good.

5. Same black almost wet residue in the end of the rear exhaust muffler.

That's it, and when I pulled the rear spark plug immediately after the run there was a nice slow trail of smoke coming out the plug hole....

I'm starting to think I'll pull the rear head and replace the rings on the rear cylinder, and while I'm there get the valve guide seals checked, even though they were replaced during the build.

 

The oil level looks to be almost to the top of the oil tank, minus the filler neck. Are you sure you just don’t have to much oil in it?

 

no, I checked the level again and it's just below the full mark on the dipstick

 

FWIW, an overfull issue would effect both cylinders