|
|
|
Rebuilding a 2 stroke?
- Thread starter unL33T
- Start date
It's about $150 USD from AF1 racing. Haven't checked my Canadian sources yet (thanks for the reminder!). I didn't get a pic and bitzz told me he smoothed it out before reinstall so it's probably hard to see what the damage was but I'll take a pic when I swap it for the new one. I think he also said it was showing wear, anyway.
Missed that step. Will redo.
Not yet. Like 250.
Didn't ride much last week because it rained so much.
As Matt points out 90 is way too low.
When I rebuilt my son’s RS the first time I got a B oversize (0.01mm) piston had Vance at Precision Cycle hone it to fit. Pistons for plated cylinders come in very small increments so when the plating wears you can go to the next size up with a hone.
I have a note in my manual here that when it was rebuilt the static compression was around 146 PSI. The second time I rebuilt it I had the cylinder re-plated by Millennium and used a Wossner kit. I also had Precision Cycle cut the squish and dome properly. After that the static comp was around 170 psi according to the note I have here.
According to the manual the piston to cylinder clearance should be between 0.02mm->0.035mm clearance so I would check that.
Is it an OEM base gasket? If not is it too thick?
I have also noticed that on the aftermarket Athena barrels the machining is not great. When I did my RZ421 the first squish measurement was 1.9mm. I can’t comment on the Mitaka barrel as I’ve never used them and it does look like a nice piece of kit, but what was the squish after you rebuilt it?
Are you still using the OEM head or aftermarket?
When I rebuilt my son’s RS the first time I got a B oversize (0.01mm) piston had Vance at Precision Cycle hone it to fit. Pistons for plated cylinders come in very small increments so when the plating wears you can go to the next size up with a hone.
I have a note in my manual here that when it was rebuilt the static compression was around 146 PSI. The second time I rebuilt it I had the cylinder re-plated by Millennium and used a Wossner kit. I also had Precision Cycle cut the squish and dome properly. After that the static comp was around 170 psi according to the note I have here.
According to the manual the piston to cylinder clearance should be between 0.02mm->0.035mm clearance so I would check that.
Is it an OEM base gasket? If not is it too thick?
I have also noticed that on the aftermarket Athena barrels the machining is not great. When I did my RZ421 the first squish measurement was 1.9mm. I can’t comment on the Mitaka barrel as I’ve never used them and it does look like a nice piece of kit, but what was the squish after you rebuilt it?
Are you still using the OEM head or aftermarket?
The Mitaka pistons come in a range of sizes with very minor increments of 0.01mm and have to be selected properly to suit the bore as the plating and cylinder diameter varies.
https://www.pjme.co.uk/acatalog/Aprilia_RS125_Engine_Top_End_.html
Was this done? I've seen this on MX bikes where even though the barrel and piston are brand new, the clearance is way out of spec as the piston is too small.
IMHO, and you will get a lot of opinions about this, I prefer to buy the smallest size piston and send it with the old barrel to a good plating shop. That way they can build up the plating and hone it exactly to fit.
Your original barrel didnt look too bad, you want to see some of the MX cylinders I've had refinished. I would definitly keep it as a spare and you can get it plated if anything happens to this one
https://www.pjme.co.uk/acatalog/Aprilia_RS125_Engine_Top_End_.html
Was this done? I've seen this on MX bikes where even though the barrel and piston are brand new, the clearance is way out of spec as the piston is too small.
IMHO, and you will get a lot of opinions about this, I prefer to buy the smallest size piston and send it with the old barrel to a good plating shop. That way they can build up the plating and hone it exactly to fit.
Your original barrel didnt look too bad, you want to see some of the MX cylinders I've had refinished. I would definitly keep it as a spare and you can get it plated if anything happens to this one
CV Tech in Quebec
If you're going that route I suggest you send them the trashed cylinder to fix and replate... that way you have a spare cylinder. I think about $500 with a new piston and top end gasket kit.
Is the bike running hot? If you were getting "blow by" the motor would run hot.
That's about the same price as the kit from AF1.
It doesn't seem to be running hot. Normal 3 bars on the temperature display. Did go up to 4 a couple times this week when stuck in traffic but that's not unusual. I'll see if I can find another compression tester. Anyone have one I can borrow?
Hmmmmmmmmmm
1) 12.5 x atmospheric pressure (about 14PSI) is 175 PSI... so to get 175 PSI on a compression test you would need 100% efficiency.
Yaa want tell me how to get 100% efficiency? at the couple of hundred RPM the starter gives us? Two stroke, four stroke or a system designed by you... it ain't gonna happen.
2) That 12.5 compression ratio (I actually lowered it to about 11.7 or so) is the swept volume of the cylinder divided by the volume of the head. Now; look at the picture of the cylinder that unL33t posted. Half of the swept volume HAS AN OPEN EXHAUST PORT... you know where the compressed gases escape from.... yeah yeah THAT OPEN PORT.
Think about that for a moment.
Sticking a pressure gauge in the sparkplug hole of a two stroke DOES NOT tell us what the compression of the motor while running. There are just too many variables
1) 12.5 x atmospheric pressure (about 14PSI) is 175 PSI... so to get 175 PSI on a compression test you would need 100% efficiency.
Yaa want tell me how to get 100% efficiency? at the couple of hundred RPM the starter gives us? Two stroke, four stroke or a system designed by you... it ain't gonna happen.
2) That 12.5 compression ratio (I actually lowered it to about 11.7 or so) is the swept volume of the cylinder divided by the volume of the head. Now; look at the picture of the cylinder that unL33t posted. Half of the swept volume HAS AN OPEN EXHAUST PORT... you know where the compressed gases escape from.... yeah yeah THAT OPEN PORT.
Think about that for a moment.
Sticking a pressure gauge in the sparkplug hole of a two stroke DOES NOT tell us what the compression of the motor while running. There are just too many variables
|
|
|
|
|