I bore scoped my cylinders and posted about it a while back. There's a fair amount of carbon build-up. I was told it was mostly normal for an engine breathing in crank case vapors.
I re-routed to a catch can. I've ridden a few hundred miles, and there is no trace of oil in the can, just a little moisture with a hint of gasoline. I think oil from the breather is not the cause of the carbon build up.
I guess this could be oil leaking around a valve. I guess I'll be doing a compression test, then add a bit of oil to the cylinders and see if the number changes much. That should show if it's rings or valves. Won't tell me about a leaking valve seal though. What's the easiest way to check that?
I bore scoped my cylinders and posted about it a while back. There's a fair amount of carbon build-up. I was told it was mostly normal for an engine breathing in crank case vapors.
I re-routed to a catch can. I've ridden a few hundred miles, and there is no trace of oil in the can, just a little moisture with a hint of gasoline. I think oil from the breather is not the cause of the carbon build up.
I guess this could be oil leaking around a valve. I guess I'll be doing a compression test, then add a bit of oil to the cylinders and see if the number changes much. That should show if it's rings or valves. Won't tell me about a leaking valve seal though. What's the easiest way to check that?
The head breathers WILL cause more carbon build up on the cylinders than if they were vented to the atmosphere. That has been documented. The more bypass through your particular engine's breather system, the more additional carbon build-up.
Changing the breathers to the atmosphere doesn't immediately, or significantly remove the carbon build up that was already in place. 100 miles with a rerouted breather system won't make any difference to your carbon build-up. Depending on your backing plate, and how the breather passages were re-routed, you could still have residual oil from before the change in the air cleaner system.
All that doesn't mean you couldn't have an additional issue with rings, valves, or valve seals....
A compression test is good, but if compression is low, it won't tell you where the compression is going.
To find out where the compression is going, you should do a leak down test. You can buy, borrow, or rent a good leak down tester. It basically pumps about 100psi into a cylinder. It then tells you what percentage of that pressure is leaking out of the cylinder.
If you hear air escaping out the exhaust- you have a leaking exhaust valve.
If you hear air leaking out the air cleaner/intake- you have a leaking intake valve.
If you hear air leaking out the external breathers or the oil fill- you have air leaking past the rings.
You may not have a problem, but if you want to check.... do a compression test and then a leak down test.
If the engine is performing well and there is no excess oil consumption, there is no need to go looking for a problem.
Just make believe you never looked into the combustion chamber, and ride...
When the breather system was in stock configuration, I could always find some oil in the intake area, but since I routed the hoses overboard I have never found so much as a drop of oil on the end of the hose.
I suspect the OEM breather system can actually draw a bit of oil because of the low pressure in the intake.
On an unplanned teardown of the engine in my `19 FLHT, the piston tops were coated in a fairly thick layer of carbon, it took quite a bit of effort with a plastic scraper to clean the crud off.
I don`t think it would have ever come off without scraping it off.
I would have done nothing to clean them if the engine was assembled.
1. What do your spark plugs look like?
2. Do you have a tuner on it?
3. Any changes to the exhaust or air cleaner?
4. May be running rich - spark plugs will tell.
10-04-2024, 10:14 AM
Where's the carbon from?
