issues with fresh MHR dio build

[LMH]

Make a YouTube video could be bearings, if it were clearance you'll know first rotation by hand.

[Wheelman-111]

Greetings:

Take off. Cylinder. Check piston skirt. It may be hitting at bottom dead center. Just shave the skirt to remedy.

[LMH]

That skirt wont hold up that long to be running 5 minutes banging, and then for it to go away off idle def sounds like crank case bearings and not interference. Who knows, shave it down on a belt sander a mm it cant hurt, just chambfer the piston after. With it only being a 44.4 your only +1.5 on the down stroke so as long as you used at least that on base you should be good.
Ive heard the sound of almost like detonation after doing a kdx200 rebore and stroking, the bearing on the clutch side was bound just enough to make noise at idle only once any throttle applied it went away. I thought it was piston slap and the rings didnt seat. After new rings again and checking clearances 5-6 times I decided it must be bearings and it was.

[LMH]

yup brand new bearing from kawasaki and felt solid and thats what it was tho. Honestly your problem could be 20 things.

[LMH]

Yup more than likely when the crank was installed into them it bound, but who knows, I do know its not the first time brand new bearings were not good upon installation. youre going to see 4 marks on the crank and piston skirt, if you see none I guarantee its not a clearance issue, anything rotating that long and that fast hit each other will leave a permanent mark and damage.

[LMH]

Also personally I wouldnt run a piston thats been bottoming out, I would get a new one as structural damage has already happened and shaving down part of it wont help the weakened structure. You can take your chances but replacing itll save you a bore that can not be honed or over bored and having to split cases to clean out all the fun sized broken piston pieces.

[LMH]

At that low of idle most 2 strokes clank and bang, just my view on the idle rpm, but youre probably not hearing the noise Im thinking of and its probably something else. Ive never ran a 2 stroke that low of an idle from a rebuild so I dont know. A video would do good, when you do it make it from a far away point then move closer slowly so it wont get distorted too bad.

[Wheelman-111]

Greetings:

How did you obtain the 135 PSI compression? Was the carb off, or the throttle held wide-open? Reed block installed?
I'm surprised it was that low based on my own 3 Malossi setups, all of which gave numbers north of 160. I read that you spaced the cylinder with base gaskets, but still if the 135 value is falsely low, it could in fact be detonation. All the advice you got above still applies.

[Wheelman-111]

Greetings:

I just read you have an OKO 28 with 40/138 jets? Both sound pretty small for your displacement. I have (I think...) 55/150 in mine, and it's stock stroke. "Gets worse when it warms up"? What temps are you seeing idling there? How's the spark plug color?

[bakaracer]

140? are you using a cht gauge to check temps? because thats cooler than what the bike idles at after the engine gets up to temp.

[bakaracer]

140? are you using a cht gauge to check temps? because thats cooler than what the bike idles at after the engine gets up to temp.

Using a laser temp gun.

thats a very inaccurate way to check engine temp. the best is to use a cht gauge or egt. as soon as you ley iff the throttle,head temps will usually unless your pilot system is lean then it will heat spike first before dropping. by the time you stop to check it with a laser, temp would have already dropped more than 100deg from where it peaked at.

[veedubh20]

that is normal temp 140 on the malossi bore at idle.. I use laser gun temp, dont need cht gauge.

Laser gun is good to have those. a car get stuck thermostat not open. it is bad thermostat..

[tilstad]

I had a similar issue with one of my scooters, had just put on a new cylinder kit and got metallic clanking sound at idle. Thought the engine was self destructing. If I revved it a little it went away somewhat, sometimes totally.

Turned out the variator nut had come loose. Tightened it, and now running like a champ! Could be worth having a look at atleast.

[Downsouthdio]

Graphite get a cht guage.. Jet big and work down if anything

[Wheelman-111]

Greetings:

Sorry I missed the part about the 44mm stroke. MHR Compression is stupid-high with stock stroke. Add the 2.7mm to the volume of the stack of mixture and I bet it was near 200 PSI., even if you raise the cylinder, unless you enlarge the combustion chamber volume with a grinder or a gasket or 2.

Flash 6 measured over 165, still running AvGas mixture for insurance. Consider a stock stroke crank for the re-do. Yeah, "there's no Replacement for displacement", but few of us can hope to compete with Signore Malossi's porting Wizardry. The juice above 10 K makes for a respectably quick ride, substantially stronger than 72cc would suggest.