Thanks for that. I did find that manufacturers list an XT225 sprocket as having the same offset as a TY250 sprocket and happened to have one from an XT. The sprocket that came on the TY has about 5 mm too much offset. I did some measuring and my numbers are slightly different from yours but also found that different manufacturers (on Amazon) list minor differences in sprocket thickness. That seems odd.
Were the original sprockets aluminium? This one is magnetic and all references I see to the brand on line are all old so it could be a 25 year old aftermarket sprocket. Is the OEM offset listed somewhere?
Everything looks straight as far as I can tell with a tape measure, eyeball and the bike together. One odd thing is that the paint is rubbed off the swingarm where it touches but I would expect to see it more torn up from the chain. If I mis align the snail axle adjusters by one step, I get about 2 mm clearance.
I have a new to me TY250A twin shock and the rear sprocket lightly rubs on the swing arm. Do they normally have very little clearance? The bike appears unmolested and with low hours. The axle hardware/ spacers match what is shown on the part list. The rear sprocket is steel, looks original and is marked PORTCO YA-311-53. The sprocket runs reasonable true and is not bent. My attempt to check sprocket alignment with a home improvement type laser suggests that the rear sprocket is about 1.5 mm farther out than the front sprocket. Is there something else to consider before installing a 1.5 mm spacer or taking 1.5 mm off of the mounting surface of the sprocket? Purely by eye, the sprocket looks 1/4" out from the front sprocket.
I was talking about relative size of foot to calf. My latest pair are size 44 so any measurements I take would probably mean little to someone named bigboi. IIRC, Forma and Gaerne fit exactly the same except that Forma are an inch or two taller, at least in my size. The only other brand I tried was Alpinestars but they were quite narrow so got returned.
I have had the opposite experience from Lemur with Gaerne and Forma. For me Gaernes are quite soft and require little break in. In not a very long time, they start to feel as soft as bedroom slippers. The soles are also softer which may give you better traction on the pegs. I find the Forma to be stiffer and require more break-in. The stiffer feel, even after break-in, makes them feel more protective. The harder soles also last longer. I'm on my second pair of Forma Boulder and have a pair of their adventure boots. All feel the same. These are the waterproof ones and I don't know if that makes a difference. I have had a number of pairs of Gaerne but don't remember what model.
This claims 155 lbs dry. IIRC, the beta 4t is about 7 1/2 pounds heavier than the 2t models. The Honda is then another 7 1/2 pounds heavier than the Beta 4t.
I stand corrected. The number is 60 hours and came from an ISDT preparation manual put out by Lampkins. I was just following that recommendation but the clearance never seems to change. There was no failure.
I have a 16 Beta 300 4t and have been checking valves every 50 hours but they never seem to change so plan to stop. It is a lot of work to get to the valves. Everything comes off the motor except the swing arm bolt and the engine then rotates down around the bolt to get valve access. It is also quite a bit more work to get to the carb compared to the 2t. It is the quietest bike and easy to kick.
Not the same bike but I once had an early 90s Fantic 80 for one of my kids. It had full size wheels and was a full size bike or almost full size. It probably weighed as much as a current trials bike or a bit more. Power was adequate for a 155 lb person to pop over moderate size logs. It worked pretty well on the flat but any kind of a hill was an issue. Even a very moderate size hill required max rpm in first gear just to get up. Modern 80s probably have more power but when you test ride be sure to try some kind of hill.
Once again, the clutch started to drag and hot stick. I then replaced the steel plates with new Yamaha plates, it worked well for a short while but started doing it again. These plates do have the dimples. I just sanded the steel plates with 180 grit and it seems OK for now. Could it be that you need to replace the friction and steel plates at the same time? This seems strange. I also get cold stick but don't care about that.
The rear brake is the one thing I dislike about Evos. The Beta 4t has the brake on the other side yet has the same weakness. In addition, I found Rev3 rear brakes to work fine. I sometimes wonder if the lack of feel on Evo rear brakes is actually the brake lever (flex?). Or maybe it is the combination of the lever and my small feet (size 9). The picture is more vulnerable but a workable solution. I think the Jitsie lever helps a little also. Early Rev3s had a 2 piston caliper in the back. I did this after replacing all brake components including the disc and trying all available pads.
Key is to try and get an oil with a low burning temperature (flash point).
Have a look at the oils in your shop and pick one that is on the lower end of the burning temperature as Trials motors generally don't get hot enough to correctly burn the most fantastic fully synthetic oils designed for race bikes.
Where do you find the flash point? Is there a comparison chart somewhere?
The angle of rotation (back/ up) is usually different for modern trials pegs vs vintage trials pegs and all MX bikes. If you find modern pegs to bolt on they may not be horizontal on top. In addition, you need to consider kick start clearance. I widened the stock pegs. The funny angle is for kick start clearance.
Earlier Beta 4ts had a slightly quicker throttle, at least in the initial stage. I think the change happened around 2019. I have a 2016 and when I went to the later throttle is made operation with small throttle openings easier to control. I'm not sure if you can still get the old model from Beta. However, when looking for a replacement tube for my 2016 throttle, I found that the one used on KTM 50 4t was exactly the same. This may be it but the description is odd.
Attached is a scan from an old Hotrods catalog. It shows all rod/ pin dimensions for a number of YZ250 engines. I would be curious to hear if one matches your engine. The catalog also shows pins available by size but it is from 2007.
I see that Hotrods is now part of the Allballs group and still sells individual pins.
I ended up going to the Tubliss system and the issue appears to be gone. I expected mounting to be quite difficult but it was not bad. I see their claim about it being lighter. I did not weigh anything but I would say... maybe and it probably depends on the thickness of the 4:00 x 18 tube you are running. The 18" tube and two rim locks go away. You add a skinny bicycle type tube, plastic cover and lightweight rim lock/ pressure valve. Provided plastic tape replaces the rim band.
"bounced me backwards just a bit pulling on the throttle."
That is exactly what I would describe as the throttle getting away from you. In that situation, a smaller front sprocket makes the bike run out of RPMs quicker so it can sort of choke off or minimize the "getting away from you". It is cheap and easy to try.
A couple of years ago, I bought an 01 Rev3 270 with almost zero wear on the original tires. Power was very sharp right off the bottom with the initial crack of the throttle. It was much much sharper than my 2014 Evo 300 2t Factory off the bottom. (The 300 Factory sort of took off mid range.) I added a full millimeter of base gasket for a total of 1.5 mm. Then I installed the heaviest flywheel weight I could find. It was something from a Techno marked Ducati. Power delivery is much smoother and it is easier to kick. I would think anyone who likes vintage bikes like a TY250 would like flywheel weights on modern bikes.
I also find that going down a tooth on the front sprocket helps. The clutch out speed is slower so it makes clutch use easier in slow tight turns. (I'm no clutch master.) But, based on your injury description, you may have been going pretty fast. A smaller front sprocket also reduces the tendency to build speed with a series of obstacles to clear like log-log-log. If the throttle does get away from you, the bike will also run out of RPMs quicker with a smaller front sprocket so you can't get in as much trouble. I have tried 2 teeth lower but find it reduces the ability to get up and over things in first gear. A smaller front sprocket does reduce top speed if that is important.
TY250A Rear Sprocket Clearance
in Yamaha
Posted
I did not realize that XT225 = Ty250 offset until I found it on line. I only had the XT225 sprocket.