Jr80 help?

[gottagetacheaperhobby]

One of the locals in laura has given me a challenge, to sort out his sons 06 jr80. Its VERY rough, im not getting paid for labour, and he doesnt have much cash so its a love job pretty much
Its missing a exhaust stud (snapped off and then the have gasket gooed around it ) hasnt had new piston or rings since it was new, also has never had the filter oiled lol. I have had it running after a carby clean, but very poorly and no power what so ever, suprise suprise.
Does anyone know where I may find a cheap bore for it, or if older bores will fit.. I will get brand new piston and rings etc but if I can get a cheap second hand bore that fixes the exhaust stud issue, and I reckon the original bore will be shot any way...

 

[my67xr]

The cylinder is the same as a DS80 and early (pre 82) RM80, part number : 1121046400

A re-bore is only $50, so just get a new piston 2nd O/S incase the bore is scarred deep.
A snapped stud is easy enough to get out, bring it down next weekend.
Have you tried running it without the exhaust on? might be oiled/carboned up



Mick Hone - JR80 2006

 

[gottagetacheaperhobby]

It doesnt have its original exhaust, the young boy has jammed a yz250 silencer on it lmao. I will get some pics up so you can see how rough it is, when i picked it up I almost decided to leave it the hell alone!

 

[my67xr]

Drop the expansion chamber off at the head and run it, see if it rev's freely then
Don't ride it like that obviously.

 

[velociraptor]

I'll keep an eye out for a pipe if you don't find one I keep finding em after I don't need em or you can use like an 80s rm 80 muffler as mine has on it now works a bit better imo

 

[gottagetacheaperhobby]

As you can see she is pretty rough!
Would massively appreciate it if you come across a proper silencer velociraptor
My plans are to strip it down, pull the engine out and bring the bore with me to craigs saturday. Then get it bored if needed, new piston and rings, clean out the pipe, replace the exhaust stud and go from there.

 

[my67xr]

Stu, i was thinking, i have a spare DS80 engine here.
I could take my DS cylinder down to Dave's and get him to measure/bore it and order a new piston/ring's etc
Then it'd be ready to pick up late in the week, and you could take it all home with you sunday ?


That muffler on it could be modded easy enough.
Chop it down to half the length, them make up a new perforated tube the right size for the 80cc and weld it in.
Probably should repack it too


Oh and Show and Go would have a front brake lever for it too, about $12

 

[my67xr]

The JR look's a lot better than my DS when i got it.

I just pulled the head an barrel off, it look's like it could be standard bore (49.5mm), maybe 1st os ?
Wiseco has Piston's listed up to 51mm, so 4th os

This piston crown look's like it's been run without oil, more crater's than the moon!
All the thread's look fine, both on the intake and exhaust side's.

 

[gottagetacheaperhobby]

What do you want for your bore craig? That sounds like a pretty good plan. The muffler thats on it is about 10mm bigger in diameter than the pipe, spews smoke out of the join lol..

 

[gottagetacheaperhobby]

Cant believe I got it to run at all! Im not sure if this bore is saveable craig, its pretty out of shape. The scuffing has made it almost hexagonal in spots!!

 

[my67xr]

At least the bottom end still look's pretty clean.
That piston is shot, lol
Is the reed petal ok, sitting flat against the reed block ?
I cleaned up the DS80 barrel a bit to have a better look last night, both thread's for the exhaust have been fixed before.
One has a Helicoil, the other has a thread insert

 

[gottagetacheaperhobby]

The reeds still sit flush, and seem to have plenty of spring left in them. The crank bearing is still intact, but there is some sideways movement in the rod, no up and down play though. I reckon it wants the crank replacing but I know he wont be keen on it. I will get some pics of the scuffing in the bore, see if you still want it craig, I dont want to lump you with a un useable bore.

 

[my67xr]

Ok, see if you can measure across the widest point of the bore, see what it is
Maximum conrod deflection side to side is 3mm

Did you still want me to go ahead with the rebore, new piston, gudgeon, bearing and clip's
We'll work out the JR barrel later

 

[gottagetacheaperhobby]

Will measure it soonand let you know what it is. If you dont mind, go ahead with the re bore etc on your barrel so its done.

 

[gottagetacheaperhobby]

48.89mm was the biggest measurement I came up with craig.

 

[my67xr]

This is how the DS80 barrel look's after a quick bead blast through the port's and a quick scuff with grey scotchbrite.
There's a couple of fine scratch's and some alloy embedded onto the bore where the piston had started to drag.
And you can see the previous owner's repair's on the exhaust thread's, a Helicoil and a thread insert, the repair's aren't the prettiest but they'll work.





View attachment 12210








This is the gasket set, it's missing the exhaust gasket but i have a good used one you can have

 

[gottagetacheaperhobby]

I can only see the first 2 pics for some reason craig? All good anyway gets this poor bike running again the owner is going to pay me back for the parts so im not losing out, just have to wait for the cash lol

 

[my67xr]

 

[mikkh]

Craig, what kind of hone did you use for it?

 

[my67xr]

I didnt do it.
It's done on a Sunnen cylinder honing bench with something like this