T250 high speed questions

[relic]

Hello all,
I've put 1000 miles on my 1972 so far and have been trying a few things to sort out the lack of performance. I posted a few weeks back and appreciate your replies. Here's where I'm at now ---
When I rescued this bike, one of the first things I did was a compression test. I wanted to have some indication that she'd run before I invested the time and money. At that time I had readings of 125psi and 110psi. The bike hadn't run in I don't know how long, needed crank seals and the cylinders were dry. I went ahead and did the work to make the bike road worthy, (and looking less like a dog's breakfast) and it starts and runs great. The only engine work I did was crank seals, new points, coils, HT leads/caps and sonic cleaned the carbs. Air filter is stock pleated paper. My top speed is around 60mph and much less against a wind or climbing a hill.

I've played with main jets, (110 is stock), I've gone richer all the way to 125's and leaner to 105's with no improvement. I've cleaned the petcock screen, (there was some rusty crud) and my inline filters are clear. With the 110's I get the best plug readings. They look about a close to perfect as I could ask.
I did another compression test now that I've got some riding in and the results are nearly the same, left 125 and right 115psi.

I'm guessing they should be closer to 140-150psi?

My plan is to pull the top end at some point, (maybe end of the season, maybe sooner) and do what's needed. Either stock or if I can find a reasonable deal on 350 parts, I'll do it up with those. (I have an ad on this site)

But in the meantime --- Funny thing too is if I'm running at 55-60mph in 5th and up shift to 6th, she'll hold 60-ish but if I try to accelerate it won't. If I twist the throttle to WOT it can't pull more rpm and the speed starts to drop off. So I down shift to 5th and strangely it continues to have no power and slows more. After a bit she'll begin to pick up and revs start to build and again I can reach 55 - 60, still in 5th.
Hard to explain but its almost as if when I WOT it in 6th, it loads up and needs sometime to clear itself (or whatever) before it will rev again.
The tank cap vent is clear, float heights are checked.

Any thoughts?

Ken

[Alan H]

Partially blocked filters inside the fuel tank?
Remember that these bikes don't like lower revs in high gears.
They are happy at 7000 rpm+ when going for it as that's where they develop their power. 29/30hp @ 7500 rpm IIRC.)
Best ridden by a 110lb 21 year old!

[ConnerVT]

Best ridden by a 110lb 21 year old!

That was my first thought. My T500 rides like it did 35 years ago (with my 95 lb girlfriend on the back).

Wouldn't think fuel starvation would be the cause. True, some problems arise when the bowl gets low. BUt different symptom than just not pulling hard (in fact, my bike seems to run great when I forget to turn on the manual petcock, just before it stutters and dies).

[relic]

Thanks guys.
New development on this morning's ride. She was working fine, running about 55mph on the highway, working pretty hard as I had a bit of a headwind. But nothing too severe. About 30 minutes into the ride the clutch began slipping, just for a split second. Making the bike jerk every once in a while. Slowed down, dropped a couple of gears and all was fine until I got back up to speed.
I stopped for about 20 minutes, checked gearbox oil, right on the full line. After waiting turned around and headed for home. For the first while all was good again but the slipping started and this time got worse. The revs would flare up for a second or two then she'd grab and go ok. I found that if I stayed around 45mph in 4th it worked well. Got me home.
As I slowed down to a crawl, (off the highway) I could hear a rattle sound. Stops when the bike is stopped, as soon as the clutch is engaged and the bike begins to move I can hear it. Just as loud on the left as on the clutch side.
Pulled the cover and could smell the clutch but after a close look there is nothing to report. Plates, are not burnt, friction plates still over minimum spec and spring length is good. All was tight. (with the noise I was hearing I was expecting to find hub or basket issues)

What I do have though is a bad feeling when I rotate the main shaft by hand. Its not rough but almost sounds like a bearing is piling up and the balls/needles are catching in the cage. I drained the oil (its got a thousand miles on it) and not too much to see. Possibly some material in it but hard to be sure.

So I guess I'll be into this motor before I planned. I do have a complete bottom end from a T350 although its condition is unknown until I split it. Too bad as our riding season is just under way. But I'm glad it happened now as I'm leaving next Thursday for a few days and had planned to take this bike. The annual Canadian Vintage Motorcycle Group rally is on next weekend and its about 400 miles each way for me. Good thing I've got other bikes

Just a thought --- I wonder if the strange trouble I described in the first post was a bearing beginning to bind up and then let go?
It did seem at times when it happened almost like a brake was dragging. Guess I'll know more once I'm inside. I'll update when that time comes.

thanks!

Ken

[relic]

Link to a short video of the noise.

https://youtu.be/G4PM41HXGnk" onclick="window.open(this.href);return false;

Ken

[Alan H]

Oh dear.

[relic]

Have today off work so I dug in this morning. I was hoping to find a "smoking gun" but what I'm seeing is more subtle. Hard to see in the photo but I believe the trouble is with fifth gear on the drive shaft, (fifth driven as per the manual). There is discoloration on the shaft where it got hot and although not galled yet, it has the feeling of hanging up at times when I spin it by hand and slide it back and forth.

I'm off now to open the 350 bottom end I have. Hopefully its in good condition.



Ken

[Alan H]

Build the 350 and stick it in the frame. Leave the 250 stickers on.
It will be a bit quicker, but lots more torquey.

[relic]

Build the 350 and stick it in the frame. Leave the 250 stickers on.
It will be a bit quicker, but lots more torquey.

I'd love to Alan but the 350 was given to me with the cylinders, carbs and heads missing. And they've been off for a long time with the bike stored outside. It would need a lot of attention. Plus no tank, no seat and the rest of the chassis is in poor shape. That said, I have used several small bits from her so I'm glad it came my way. And now the 350 gearbox is in the 250. Well the complete shafts are...
They looked to have very few miles, no wear at all. Even the shift forks have no sign of use. So hoping that this will solve my problem. And that I haven't created any new problems with all the work I did today.
I've just now quit for today. Another hour will have me trying to start the bike but that will have to wait for tomorrow evening as its back to work in the morning.

You are right about the 350 though, if I could find a deal on a complete top end either usable or rebuildable I'd be interested. As I mentioned in an earlier post I'm off the CVMG national rally on Thursday that hosts Canada's largest vintage bike flea market so I'll keep my eyes open. As with most of these things they cater to the British and American brands more than the Japanese but you never know.

Ken

[Vintageman]

Sounds like you need a fresh top end. You can get a "feel" by using your hand. If you move the kick starter to near tdc but don't go around a few times fast it should feel springy each time indicating little blow bye. When you just go through tdc with a snap motion, it should have a nice pop pushing the piston down until exhaust opens. The top end noisy?

Compression sounds low.


Clutch slips If the plates are glossy or have rust spots it will slip. I think the (G)T250 had softer spring than T350. Clean up clutch plates good and use the T350 springs.

There was a t350 cyl set on ebay yesterdayish for $150. Almost bought... gone now. There is a T305 set but I think ~$900 with shipping. I think Paul Miller has a t350 set. Either t305 or T350 would give you torque at 4krpm same as 250 does at its peak!.

Y

[relic]

The saga continues...

After assembling the gearbox with the shafts from the 350 parts bottom end the bike ran fine. I rode 49 miles between Tuesday evening and my commute on Wednesday. It shifted better than before and ran as good as it ever did for me. And none of the symptoms I experienced prior, (clutch slipping etc). Based on this I made the decision to go with my original plan and ride the bike to the vintage bike rally last Thursday through Sunday.
My ride starts out with about 80 miles to reach the ferry that connects Manitoulin Island with the Bruce Peninsula here in Ontario. After the ferry ride I have another couple of hundred miles to reach my brother's place (near the rally site in Paris Ontario) and from there we attend the rally together each year.
About 120 miles after I got off the ferry my motor locked up. Thankfully in a small town that had shade, (temps were in the high 80'sf), stores to buy a drink and a public library with a washroom...at my age when you gotta pee, you gotta pee! A few miles either side of this town and I'd have been waiting on the side of the road surrounded by farms.
I called my brother who rescued me and the bike, we attended the rally and I'm now back home with the bike thanks to the lend of his truck.
Engine out and disassembled and the right crank bearing is noisy and rough when turning by hand. The right piston bottom ring broke near the locater pin and damaged the cylinder in the transfer port area.
It doesn't appear to be lack of oil. I filled the tank before leaving and its down about a third. (I had the tank off when I did the gearbox repair). I had bled the pump and confirmed no air in the lines when I started it. As well I added some oil to the gas for the first tank full. There is still oil dripping out from the lines into the cylinders and outer bearings when I took it apart.
The right cylinder was the one with the lower compression all along.
So lesson learned, when you don't know the history of a bike its probably best to suspect the worst and budget for a total tear down. Although this one started and ran pretty good from the first try.

So now I guess I'll watch for either 350 parts (preferred) or 250 parts as I really like the bike and am committed to having it running.
I got it for free and invested about $900 Cdn so far.

I know markets vary around the world but this bike, in good condition would be lucky to bring $2000-2500 Cdn. Small bikes just aren't worth much here.
I'll update the forum when progress resumes.

thanks for all the comments and advice, I appreciate it very much!

Ken

[Craig380]

That's bad luck, sorry to hear about that. On well-used pistons the ring pegs can get worn, or even pop out, and allow the ring end to snag in the port. At least you're OK - if the motor locked up while you're in a corner, it could chuck you off.

[relic]

Well it took a month but my T250 is back on the road. I replaced the outer crank bearings and once again the crank seals. And I found a good used cylinder on e-bay for a fair price. I had to wait for it to arrive before purchasing a piston and ring set, (to know what size I'd need). After a quick hone of both my original left cylinder and the e-bay right cylinder I measured them up and they were virtually the same. No taper and out of round was almost nil. Clearance was under .003", (spec is .0022-.0026 with .005 being the limit according to the service data publication) so I went with an NOS OEM standard size piston and a complete set of rings.
Since finishing the assembly last Saturday I've clocked 140 miles of break in time, (starting first with some heat cycles).
Its great to have the bike up and running again! And its running better than ever.



(that is my buddy with his 1946 Indian Chief. We make quite a sight riding together and when we stop its interesting to see which bike gets the most attention.

Relic