A bit of a delay with the project, well two delays to be accurate. One is my usual problem with getting side tracked with other projects, one of which was currently taking up a bit of time. The other delay is breaking my knee in two places, 6 weeks of no weight allowed on my right leg of which I'm about half way through. Since this is the third operation on this knee over the years I'm actually obeying the doctors, getting kind of worried about the state it's getting into.
I've puled the engine apart and it's about what I expected. Water has got into the bottom end and it's not a pretty sight. Typical of small two strokes it has a hardened con rod and crank pin with loose rollers, these are all very rust pitted. The main bearings (bronze) and crank are worn.
I've made up a tool post grinder for my lathe and re-grinding the crank for the mains has gone well, I've bought some lead bronze to turn up the new bearings. I've had problems with lead bronze with main bearings in the past as it can expand quite a bit as it gets hot, with my Ariel the main bearing expanded in the alli. casing stretching the alli. I had to bore the casing out and make a new bearing with a steel sleeve which has been fine for around 6000 miles. Probably why BSA / Ariel made the bearings sleeved in the first place??
Fortunately the M/Debon engine has steel sleeves which have stayed in the crankcases so happy days! The bearings are also pinned through the thrust face so I'm happy to use lead bronze for them.
I have ground the crank pin down more than a couple of mil. and pressed on a bearing sleeve. I now will make a mild steel sleeve to press into the pitted con rod to take up the slight eccentric worn in the 'ole, this I will bore out to take a needle roller bearing. I have a bit of a concern with the bearing as the rollers are quite a bit narrower in width than the original, the overall width of the bearing is the same. However................ How hard am I going to ride this thing and how many miles am I going to do on it? I have a plan B should there be problems, but want to try the roller bearing first as it's cheap and simple.
The bore and piston are in very good condition but the rings were seized in solid. After much soaking and gentle prodding I've got them out. If this was a 4 stroke I would make new ones straight away, but for now I'll run with the old ones. I have a Bantam which I've played with a little carb and porting wise, the piston slap has to be heard to be believed! Compared to other Bantams the compression is down but the bloody thing flies (well by 125 Bantam standards which ain't a lot!). The new small end is a simple turning job, the gudgeon pin is good.
This engine is so simple that pulling it apart in the future is a nothing job, first I want to see how the big end holds up. Whipping the barrel off to make new rings in the future if needed isn't a problem.
Thanks for the suggestion to tig weld the barrel, I've had a tig for years but never tried cast iron with it, don't know why?? Anyway I had a play with a scrap Bantam barrel ( the missing fins on the M/D will be coming from this) and am kicking myself for not using tig for iron in the past!
I haven't looked at the gearbox as yet, it selects all three gears but there's a lot of end float at the clutch as the gears are selected.
As soon as the leg's back in business I'll get stuck into it again, getting really bored not getting into my garage / workshop, but my wife's guarding the door armed with a cast iron frying pan with a mean look on her face!
Colin
