Possibly Problematic Engine Noise (Wombat engine)

[TheAceWombat]

So I recently finished up the light issues and small things on my Ace 100 B+ with the Wombat engine inside. Now, I want to be able to ride it but I am a bit worried about wearing it out since the engine makes a noise that I think isn't normal. Since I know almost nothing about engine noises (and my last bike made the same noise, so do many online) I wanted to pass my Youtube video by you guys and see if it is normal or not. It sounds like piston slap or something is happening, but again I don't know much.

Link:

https://youtu.be/U2pdEwkaLuM

[viclioce]

It sounds like your idle is too low and the engine is struggling to run. Raise the idle up a bit and it may sound fine. Victor

[TheAceWombat]

Well you would be right that once it is warm the choke kills it. So I suppose it idles weakly. It does have enough power to move in first with closed throttle though (and not die). So overall I'm happy with the idle. The point of the video was that ticking/clacking noise that you hear by the cylinder seems problematic to me. That is the worry. The actual running/idling seems fine.

[Bullfrog]

Sounds just like mine. I didn't diagnose anything out of the ordinary. How's the compression?

Ed

[TheAceWombat]

As far as I know, fine. It seems to have decent power and the engine has plenty of resistance when kicked. I'm not sure if I ever compression gauge tested it. Probably not since I can't remember the numbers.

[Bullfrog]

You had pretty good recordings of sound . . . but long distance diagnosis is . . . well, STILL long distance diagnosis. So, based on what I heard (by long distance) and your assessment of other engine characteristics (compression, general operating characteristics, etc.) . . . it seems like things are in good order. (Certainly no "red flags" in the sounds I heard.)
Ed

[TheAceWombat]

Ok, good to know. Thank you for the assessment and help.

[viclioce]

I agree. Probably because of the low idle, your actual combustion may be sounding like a knock, when it’s just the fuel firing off. A little bit higher idle will probably make it sound like what you think it should sound like. And, happening more times per minute will eliminate the space between power explosions! Victor

[Bruce Young]

Hello, Old two strokes with iron cylinders and steel exhaust pipes made a lot of extra alarming sounds, if you will note later Hodakas and other vintage bikes started to use items to suppress the sounds, rubber pieces in between the Cyl., fins and etc. And better baffling in the exhaust,s . These sound,s are also exaggerated at Idle when lubricants are at their lowest point in the mix. I agree with ED and Victor, that a good test of compression, and leak down test might help make sounds more understandable. Error on the side of knowledge. I am not saying don,t worry, but do the test then listen with knowledge.

[taber hodaka]

Many a hodaka engines have been run with loose bolts holding in the engine, make sure they are tight. That engine sounds so good, you do not get that sound with poor compression. The low speed carb tuning is spot on to idle that low. If everything functions well at the other speeds, I think you are good to go. -------------- Clarence

[JPark]

I disagree that lubrication at idle is low. Oil leaves exponentially with rpm, which is why you need a richer ratio in road racers while trials bikes can run on a quarter as much. Prolonged idle will load up an engine with excess oil, which is why injection systems often run a rate that varies between 100:1 and 20:1.

Four stroke engines will have a spark timing between 10 degrees at idle through 35 or more at speed. Two strokes run a fixed 25 degrees or so because they can get away with it. At low speed there is so little efficiency and so much leftover exhaust gas that the advanced ignition will not cause knock. At high speed more advance would tend to melt the piston which lacks the rest stroke that four strokes have. The only advance mechanisms I've seen on two strokes are on engines with electric start. A high compression two stroke will often be high strung at idle.

I borrowed an Ossa Pioneer a half century ago and noticed that the timing seemed over advanced. The owner seemed unconcerned. Riding it home in traffic one day, I was waiting to turn left for a while and the engine almost hiccupped out. When the opportunity arose, I punched it into the opening. The bike went backwards and my tender bits ended up on the gas cap. It ran the same backwards as forwards. The car behind was a Citroen - that French thing with the long clamshell snout. The back wheel had climbed halfway up the hood. I removed my bike and the irate owner only calmed down when I pointed out that, except for some rubber marks the hood was just fine. Luckily for my anatomy it wasn't a truck. And coincidentally, the owner of the Ossa also had a Citroen. You had to wonder.

The same bike showed up a year later at a shop I worked at 'presenting' with a holed piston and a crankcase full of aluminum. The flywheel key had sheared and the the timing had been shifted. You could check it with the marks, but the relationship to the piston was something else. Ossa's solution was to torque what looked like a 35 ft lb nut to 75 ft lbs. The cause of the problem was making the flywheel out of brass and then not having a big enough taper to hold it.

[TheAceWombat]

Update on the compression and other stuff. After about 7 kicks the highest reading I got was 130 psi. Seems fine to me. Not sure how tight the gauge needs to be in the plug hole but it was only hand tightened, so it might have leaked a bit. Spark plug looks great according to the reference pictures I've found online. Seems that the mixture is perfect. I have 36 miles on the trip meter now so I'm sure if anything bad is going on it would have been showing signs by now.

Thanks for the additional input and help all.

Also, thanks again for the voltage regulator Bruce (bought it from you months ago), I finally got it installed recently and the lights are working perfectly now. Glad to see this thing fully functioning