Super Jet Cylinder wall scuffs/scoring Help Please.

[amitchell]

I bored to 82mm this summer after my pulse fitting on case broke and lean seized at WOT (awesome) . I used pro-x pistons with 0.0045" clearance for the new bore. A few weeks later (4-5 tanks of fuel) got a new head and noticed lots of scuffing/ scoring, decided to have it honed. Here I am now after that hone with the same issue of scoring and scuffing maybe 3-4 tanks of fuel after hone!

I think I can get away with another hone, but I want to try and fix the problem.

Any Ideas on cause?

 

[amitchell]

Does this look like water intrusion?

 

[Proformance1]

Going to need more info. What are you measuring bores with? where? Where are you measuring pistons? with what? Pict of pistons. whats you ring end clearance? etc

 

[amitchell]

Machine shop used mic and bore gauge. I confirmed with two F eeler gauges 180 degrees apart placed at deepest section of skirts and dropped piston through bore. I am going to take the cylinder and pistons to be measured again.

Ring end clearance is 0.014in - 0.015in measured with F eeler, ring pushed into bore with piston crown. measure at both top and bottom of bore.

Pistons showed slight scratches that I lightly sanded at 45deg angles with 600gt according to yamaha manual. I didn't take pics of piston pre sanded.

 

[amitchell]

Here are pics of pistons now.

I had two 46mm buckshots (running rich) installed with tau cetis, switched to dual 38's with oem flame arrestor.

compression was even 170 when pulled. Ada head 37cc domes.

 

[amitchell]

I had the machine shop measure it up today.

Each bore measures 3.2295 - 3.2300in 0.0005in out of round.

Each piston measures 3.2240in

Should I deglaze/hone and replace rings or bore to 82.5mm?

 

[kevbo]

Machine shop used mic and bore gauge. I confirmed with two F eeler gauges 180 degrees apart placed at deepest section of skirts and dropped piston through bore. I am going to take the cylinder and pistons to be measured again.

Ring end clearance is 0.014in - 0.015in measured with F eeler, ring pushed into bore with piston crown. measure at both top and bottom of bore.

Pistons showed slight scratches that I lightly sanded at 45deg angles with 600gt according to yamaha manual. I didn't take pics of piston pre sanded.

The piston got a little tight but nothing out of the ordinary. At .0045 you should have opened the top screws for several tanks. Put it back together and run it.

 

[amitchell]

Thanks for the help!

No worries about that clearance jumping to 0.0055 as measured today? only 8-9hrs use since bore.

I told the machine shop to deglaze and I have new rings to put on.

 

[Nuklear6]

.0055 no problem. deglaze that cylinder put the new rings in (check end gap of course .015 is good). But I would check cooling system. Make sure the freeze plug isn't missing from the cast fitting on the cooling outlet of the pump. Seen that missing andcause lack of cooling volume and pressure. When it scuffs in the middle of the bore like that and piston tops show no signs of spike in egt it's most often cooling or oiling issues.

 

[amitchell]

I added dual cooling after I got it honed last time. Head/exhaust mani temps were about 115-120f measured with infrared. I think I will try a different oil. I was using west marine premium tcw3. I have some maxima 927 I just don't like it in colder weather because it separates. maybe klotz will be better in the cold.

 

[Fro Diesel]

I recently switched to amsoil randomly bc I forgot the usual mix. Found a good price near the lake and ran it. Seriously felt like I noticed an improvement in both skis (piped stockish 701s). I will be running amsoil when cold from now on.

My usual mix is Quicksilver 45:1 with 4oz of blue ethanol fix additive (can't remember brand) per gal of oil. Shake everytime before mixing in gas.

My ride buddy had bought some valvoline outdoor oil tcw-3 but when I opened it it smelled horrible burnt rubber smell. I don't even want to run that oil in my weedwhacker or lawnmower.

 

[CRJ]

ive been told to run near 25:1 for the first tank of a ski, keeping the rpm low, and also letting the ski warm up before grabbing a fist full of throttle. almost looks like your jumping on it right away from cold, and the piston is expanding faster then the cylinder, closing up your gap and giving you the issues. thats why there are few scratches, only happens when you first start the day

i can also vouch for amsoil. only oil i run now, amsoil HP. ive been running 50:1 but am going to drop to 40:1 to get more lubrication on my new setup.

 

[schicks]

^^^x2 , gotta let em warm up or scuffing will occur,