Exhaust blowby, engine wall damage
Hello to all,
Today i wanted to check my powervalve to see how it was set up. It was flush with the port and with the exhaust so I assume it was dremmeled out?
The bike rides fine and pulls nicely.
However I noticed that my exhaust would drip some oil from time to time but now i see the cause.
I bought the bike with proof of a new piston,honing service, gasket set and top end bearing install but this does not look like it's done correctly.
He said he had not ridden it, just to test to see if it was al good. I personally put less then 1000 miles on the engine and not driving it hard.
I assume the rings do not properly seal and that a new cilinder ans piston would be the right thing to do.
What do you guys think?
Calum last edited by
Two strokes are oily by nature. Oil dripping from the engine is not a concerm since the oil is i. The fuel amd not all fuel is burnt.
Also the oil needs to coat the cylinder walls and stop the metal rings touching the walls. So oil in and around the rings is to be expected.
@Calum So are you suggesting nothing seems off here?
Maybe use some better quality oil?
The previous owner topped it off so no idea what was in it.
What about the marks on the cilinder wall?
declan last edited by declan
@crosserke yeah better oil, your pv sits flush since it's essentially not in use, when the engine fires up the valve will rotate and partially block the exhaust port everything looks fine other than the dark piston I've never had one of my pistons be so dark on the walls,your cylinder walls look perfect if I had to guess I'd say the bore was redone but used the old piston
Hi @declan, thanks for the input! I was worried it would need a new top end. Of course the bills are not proof that he actually installed it. But the gaskets look new to me. The bike has 18k km right now and 800km on the 'new' piston. I will swap the oil first. The walls have been honed but stock piston rings are used. Maybe an oversize is required to seal that tiny bit more. I could do a compression check to find that out if anyone knows what numbers i should aim for?
I wouldn't be to concerned about the blow by on the exhaust port side. As that part of the piston obviously see's burnt gasses with it running over the exhaust port. The powervalve does look like it's had a bit of work, as the 3BN part code seems to have been ground off smooth. A new exhaust gasket might help with the drIping oil issue but not a massive issue.
Yeah I tought it has been modded too because with the ignition on I read that some had set it up aligned to the port and some to the exhaust but when I checked it, it seems flush on both sides. Any reason why people do this? I mean it's a moving part anyway and open when needed. Might not close as much as it should then for low rpm torque?
@DTR-NSR The dripping is at the end of the muffler dripping onto my wheel flinging it arround and dripping on my brake caliper after about 1 hour of riding. Forgot to mention that sorry. Hope that switching to oil suitable for direct injection will fix that too.
Calum last edited by
Two strokes are oily by nature so I'd expect a little bit oil. Oil is good. Means you're definitely getting some
He probably topped it up with some left overs telling me it's all good. Happy to see some expert toughts of you guys, thanks!
I'm always curious and supprised to see that some internal modding has been done. Not sure if it's all that positive for performance but just want to make sure it's running happy and safe.
Darty last edited by
Quick note, check the oil level for the transmission, it sounds like a failed crank-seal with all that oil.
@Darty Thanks for the extra tip. Seems ok, I replaced it as soon as I got it because I trust no one telling me it had a full service anyway
Still at the full level and the same nice red color visible trough the inspection window as when I put it in.
My bike was chucking oil out, turns out the oem cable doesn’t fit properly and is allowing too much oil in. Also the pump wasn’t closing unless you let the throttle snap shut aggressively. I’m putting it back together atm. I need to check the pump lift when it’s done. I’ll let you know if it’s a cure for the smoke/oil drip problem when it’s done...
@SpookDog I have turned the cable all the way in now. Will re-adjust after putting in the new oil and running it for a bit. Thanks
What does your spark plug look like? Healthy tan or black and oily?
I’d definitely make sure that the pump is adjusted properly before running for any amount of time...
declan last edited by
@crosserke what do you mean about turning the cable in, if the pump is adjusted too little you may seize the engine
This weekend, I tipped out the remaining oil in the reservoir and replaced it with something suitable for direct injection from Motul.
I did a short ride to get the old oil left in de tube trough and ready for further testing.
This is what my spark plug looked like before switching oils.
And yes I gave some more slack on the cable for the pump because it looked too rich on oil for me dripping onto my brakes after 15min of riding didn't make me feel safe.
I will check what it looks like right now later today.
Update on the spark plug:
This is with the oil pump adjuster turned all the way in = most slack and least amount of oil.
I noticed one drip on the cam but no oil in the casing.
Could the pump be sending too much oil in any way due to wear?
I might look into a rebuild if that's the case.
The cable doesn’t adjust oil flow. It just makes the pump open sooner or later. You want the pulley to start moving at the same time the carb slide starts to take slack off the cable and lift.
Any adjustment to flow is done by adjusting shim washers under the nut and washer on top of the pulley...
There should be a gap of 0.20 - 0.25mm when it opens and closes at tickover...
The problem with mine was that the cable outer was too long (or the inner too short) and wasn’t letting the pulley close fully. I had a gap of about 6mm, so it was always a bit open. I’ve put it back together and checked the clearance gap between washer and top of pulley, but I still have excessive smoke at tickover.
@SpookDog Ooh didn't know it works like that. Very good to know thanks! Will digg into it to see if I can check the gap.
declan last edited by declan
@SpookDog are you sure on that bud im pretty sure that it works to increase the oil flow when its actuated when i bleed mine i have my premix going and i can actuate the pump and i will get more oil flow with the vacuum line disconnected too its been a few yrs but im sure im remembering it correct i don't believe my style of pump has any available shims.