Bogging or seizure? Malossi Sport - new rings

[broyager]

I'm a bit stumped as to what's happening.

I've just replaced a set of rings, following a pretty extensive port chamferring session, plus smoothing of said chamfers.

The reason I replaced the rings was I have been wearing rings out pretty fast, and this seems to be causing audible piston slap, which is increasing in severity as the rings wear down. The ones I took out were 0.48mm

Had done a couple of heat cycles after replacing the rings, then out for a ride and didn't get far. Nothing happened but it seemed like it would have.

Seemed to be cutting out, or lean bogging, or rich bogging....

I didn't make any changes to the known working jetting I had prior to changing the rings, and have subsequently gone up and down a notch from the middle on the needle, and up a size on the main, with no change to the bogging.

There are no obvious leaks around the intake (didn't change that), none around the base gasket (I have a pretty good procedure there) and no visible spooge from around the exhaust.

I've then tried swapping the head with the original Malossi for less compression and greater squish, in the hopes I might have been pushing compression too much.

I didn't mix any extra oil in the tank for the initial heat cycles and short ride, but have added some to make around 35:1 now and still  had similar bogging, possibly a backfire when taking out to work this morning.

When I took the cylinder off again this afternoon it was very well lubricated, the plug was not wet though.

My build thread is here but current status is in my signature.

49ccscoot.proboards.com/thread/30759/genuine-buddy-ligero-daily-sleeper

Bore looks very smooth with some reasonably nasty scoring. Some of the scoring was from before I replaced the rings, but there are  definitely more there now. I had cross hatched lightly with 240 grit before putting it back together.

Prior to taking it apart I was swishing the fuel tank and a 5 min warm up before each trip.

Temps were all below 200F on each of the test rides never above 250 on any of my commutes. Possibly went above when shutting it off.

It currently starts up and idles really nicely, very responsive throttle, no hesitation or hanging idle.

Crankshaft is new and has zero play any direction.

Here are some photos of the bore and chamfers I've made. These were pretty aggressive I thought, the rings shouldn't be wearing as fast as they are on this dual ring cast iron bore, so this was my attempt at smoothing out the rings transition between the ports, plus I wasn't afraid of raising either the transfer or exhaust port heights for extra juju.

 

 

 

 

The only thing I can think of is a leak at the exhaust causing a lean condition? I have double exhaust gaskets for fit.

I'm going to re-cross hatch, and attempt to round any chamfering further. Add extra sealant around the exhaust, and hope for the best...

One thing I have noticed or realized is that there are marks on the lower crankcase halves where the skirt from probably the Naraku cylinder I had on prior pressed into the aluminium, but I have cut down this edges of the Malossi cylinder skirt to prevent this.

Also all port edges are smooth to touch except for the vertical edges, which I believe don't matter.

Anyone have any ideas?

[broyager]

Problem was a newish but faulty spark plug.....

Well at least all my port edges are now super smooth.... probably have hurt performance a bit in the end.

And I probably wasn't going to get too far with 50:1 on new rings and hand hone in anycase..

[aeroxbud]

Running 50:1 with new rings on a sports cylinder is fine. I've just done over 800 miles on my new 70cc with 50:1 oil mix so far.
That's all I ever ran on my slider with the Polini sport. Polini even recommend that.

[broyager]

Ok thanks. Yeah some of that scoring is from FOD I think.

Still rattling away with brand new rings though, the same as prior to replacing the crank..

Looking at buying the larger spec piston

This thread got me all inspired to keep going with the Malossi Sport

49ccscoot.proboards.com/thread/26897/2000-yamaha-vino?page=5

gutti indicates raising the Malossi Sport exhaust by a couple of mm's, and Zino has said he does the same on his builds with this.

I want to try and match the Stage 6 port pro, so add some material here to hinder loss between main transfers and exhaust port, if it is widened.

[jaguar57]

Power 1 is only half synthetic according to its safety data sheet (free of promotional lies) so you should use it at 35/1.

[Lucass2T]

Oct 12, 2023 22:42:31 GMT -5 jaguar57 said:

Power 1 is only half synthetic according to its safety data sheet (free of promotional lies) so you should use it at 35/1.

35/1 is knowledge from 50yrs back.
These days with modern oils you don't need to go that fat on the oil.
It's true that most of the oil brands throw around all sorts marketing phrases which makes it look like it's a synthetic oil.
The only true synthetic oils are the ones that specifically write '100% synthetic' on the bottle.
Al the rest are just mineral base oils with just 1 drop or more (they keep ratios secret) of synthetic blended through.