swooshdave Posted March 13, 2008 Report Share Posted March 13, 2008 Since the mid 70s Bultacos were 27 degrees and 76mm ground trail, and the KT250 is 26.5 degrees and 75mm ground trail (though with a just slighly shorter wheelbase) I'm not sure why the KT doesn't handle pretty much just like a Bul. Sounds like you are making the same mistake the Japanese did. If you just copy a few dimensions, the rest of it should work the same. But bike handling is more complex that just a few measurements. Steering is just one part of it. So what if the head angle and trail is the same? You still have wheelbase, swingarm and weight distribution to think about. And probably a few more traits I don't even know about. And then you need an engine that complements the chassis. The Spanish had a huge headstart in development by the mid-70s. But it was just a matter of time... Quote Link to comment Share on other sites More sharing options...
Guest majestyman340 Posted March 13, 2008 Report Share Posted March 13, 2008 If you want pictures, here's one taken at a trial (before I built the new exhaust). The tank I built isn't as nice looking as the stocker, but it is lighter and rust-free: Four KTs at a regional trial seemed like an event worth recording. They owner of the bike right behind mine rides the two line and seems reasonably happy with his bike, though when I let him ride mine after I built the pipe and did the other engine mods he did prefer the power of my bike. I have two friends here in the area that have KT250s that are nice and original and have all the lighting kit (one of those is for sale as it looks like the person is going to stick with roadracing and not do any trials after all), and I've heard from a fellow in Norway who has one with all the lights. I didn't try retarding the timing until after I did the porting and cylinder head modifications, but it is quite a bit retarded from the stock position now. I've been looking through some old magazines today, and generally the KT250 seems to have gotten the nod as being best overall (not necessarily by much) Japanese trialer. Pretty cool seeing all those full page inside cover ads for Sherpa Ts too! Since the mid 70s Bultacos were 27 degrees and 76mm ground trail, and the KT250 is 26.5 degrees and 75mm ground trail (though with a just slighly shorter wheelbase) I'm not sure why the KT doesn't handle pretty much just like a Bul. I'm going to put together a chart of all the dimensions/weights from those 70s roadtests and add that to the KT page on my website in the near future. Today I got a few sample spokes pulled out of the wheels and then chopped the rest so I'm hoping to get the hubs sent off tomorrow to Buchanan's to have rims and spokes made. They say they don't have specs so I'd rather send them the hubs instead of a drawing so that they have no excuses if they make a mistake. I did some measuring on the forks and I'm going to have to pull those apart as I think one of them may be very slightly bent. I couldn't get the assembly to be dead square on the surface plate. It wouldn't hurt them to get all cleaned up with fresh fluid anyway. I'm not sure what tire diameter they calculated trail with (it should be 702mm), but using an unmounted new Michelin front (693mm) my measurements of the fork offsetss are giving me 77mm of ground trail at full droop, where 79mm is what the manual claims. With the non-parallel clamps (1.5 degrees) at full bump (if the rake stays unchanged) trail will increase by about 5mm. The axle offset in the sliders is 24mm so the clamps are too flat to make me want to try them with center axle forks (that would be about 104mm of ground trail - a TY250 is 90mm). I'll have to see if I've got anything in the 75mm offset range as I've got some center axle Betors I could try. I do have a set of Sherpa T Betors that I'll need to look at to see how they divided up the offset between the clamps and slider. I might be able to mix and match to get some different total offsets, though there is a 1mm difference in fork tube OD I'd have to deal with. Power characteristics are the main difference I can recall between my 1974 325 Bultaco and the KT250. I'll have to try and do some swaps with people at the next trial I go to so I can get some idea of how different the various bikes feel. cheers, Michael What have you set the steering head angle at Mike? Looks quite a bit steeper than stock, and as this is something I have arranged to have done on my Majesty, I wonder what improvements you have noticed? It might be worth talking to B&J Racing regards your project, as I seem to remember they did a 300cc conversion for the KT, which might be a very good way to upgrade your motor. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 13, 2008 Report Share Posted March 13, 2008 Since the mid 70s Bultacos were 27 degrees and 76mm ground trail, and the KT250 is 26.5 degrees and 75mm ground trail (though with a just slighly shorter wheelbase) I'm not sure why the KT doesn't handle pretty much just like a Bul. Today I got a few sample spokes pulled out of the wheels and then chopped the rest so I'm hoping to get the hubs sent off tomorrow to Buchanan's to have rims and spokes made. They say they don't have specs so I'd rather send them the hubs instead of a drawing so that they have no excuses if they make a mistake. I'm not surprised hearing that the steering geometry of the KT is similar to a mid 70s Bultaco. I would describe the overall feel of the KT as being like a slightly top-heavy mid-1970s 238cc Sherpa T and the steering behaviour in very tight turns is virtually identical. The Sherpa steers better in a straight line over obstacles though. Did you try the Kawasaki shop for spokes? They are good value and you know they are going to fit without any issues. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 13, 2008 Report Share Posted March 13, 2008 Michael Sorry about the Kawasaki spokes thing. I hadn't read your posting about wanting stainless spokes. Our sections often feature tight turns and largish obstacles. Long bikes, bikes that you can't use the clutch properly in turns and bikes with high gearing don't have a chance. If the bike can be ridden slowly enough to do full lock turns and still punch strongly out of the turn, it is OK. A 15 tooth front on a KT250 would have the bike struggling on the first decent size obstacle that had no runup. I'm not saying that trials is the same all over the world, but here, stationary balancing and using the clutch in turns are essential skills for doing the turns found in twinshock class. Some twinshock riders - not me - I'm too unfit - commonly hop the front on their twinshocks as if they were riding a modern bike. I'll post another photo from last weekend that illustrates the sort of tightness found in our sections. It's not that easy to describe but have a look at the squarish rock near where my front wheel is going to land. To get the next bit of the section right, you needed to turn to the rider's right inside that rock on landing. See that I still have the throttle open doing the second blip when the picture was taken and yet have to stop inside that rock for the turn. That's why I use low gearing and have the front brakes working nicely. David Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 13, 2008 Author Report Share Posted March 13, 2008 Sounds like you are making the same mistake the Japanese did. If you just copy a few dimensions, the rest of it should work the same. Dave, you always want to keep an eye on what the competition is doing, and borrow good ideas when you can. Just maybe not to the level that happened in F1 this last year. If the KT is within a hair of the Bultaco measurements then I might be able to improve things by making minor changes like foot peg position etc without messing with raking/new triple clamps. I do normally take a tape measure and caliper and notebook to races/events as you never know what interesting things you might learn. majestyman340, the frame is stock at this time. You might be able to see that the fork tubes are pulled up in the triple clamps about .5-.75". I just took the caps off to collapse the forks and then loosened the clamps and let things slide up until the fender was almost hitting the exhaust pipe. I think that at 13.5" the Fox Trials Shox are a little longer than stock, but I don't have a set of stockers to measure. I also trimmed the fork stop just a little and since all the bikes are at full lock that may make it seem a bit steeper. I've talked to Bob in the past and bought a few small parts from him. He had one of the big bore kits left at that time, but the price was a lot higher than I could comfortably consider paying. I have looked at some different Wiseco pistons and found one that would be perfect for a bore in that area, except that it has some ports in the side of the piston skirt that interfere with ports in the cylinder. I have done very little with two strokes so I'm not sure if that could be worked around. I think that ordering a batch of 20 pistons made without that port would probably leave me with several lifetimes of extra pistons as I don't see there being a huge demand for a KT big bore kit these days. An RM370A piston might work (with a spacer as I think the wrist pin is a bit lower) but those seem pretty uncommon and are another of the many pistons that Wiseco has discontinued. If I could find a couple of suitable piston assys I do have a spare cylinder I could mess with. But right now the KT runs well enough that with a bit of extra flywheel I think it will be fine for me. I'd rather put engine development time into my TTY400 project. David, stainless tends to work harden and I think the stock spokes may actually be better as they are just galvanized steel. But they don't seem happy to deal with water and we do occasionally get to ride in some. Stainless with aluminum nipples can last a long time. But I may have to make a point of removing the tires after rides with water crossings to dry everything out. Your comment about the "top-heavy Bultaco" is interesting. I don't recall Bultaco engines being particularly light weight, especially with the heavier flywheels, so I wonder if it is a slightly higher engine position on the KT that contributes to that top heaviness? I need to weigh my Sherpa T fork assy. The KT parts seem like they could be several pounds lighter and that might be another contributing factor. The frame and swing arm can probably come down about 10 lbf at the most with a replacement frame. Getting a bike significantly lighter means chasing ounces all over once you've (often expensively) picked the low-hanging fruit where you can make big savings. "stationary balancing" is probably the big difference on the gearing as AHRMA vintage is "no stop". cheers, Michael Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 14, 2008 Author Report Share Posted March 14, 2008 David, since your bike still has the silentbloc bushings (as does mine) I'd advise you to take a look at those. It may be just because the rubber is 30+ years old but the swing arm action on mine (no dampers, just the bare frame and swing arm) could easily be classed as "mostly seized up." You should pull the dampers and maybe drop the rear wheel out so you don't have that masking things) and see how readily your swing arm moves through the normal arc. If it is like mine, the answer is "not at all readily" and that seems like it can't be a good thing. I'll spend a little time tomorrow and clean things up and check it again, but the center bush on the silentblocs should be (at 50+lbf/ft of torque on the nut) completely stationary with all movement coming from the rubber squidging about. At half that torque on my torque wrench the difficulty of getting the swing arm to move around is not at all encouraging. I'll also look to see if there are some standard needle bearing races with the right OD that could be used with some custom bronze bushings and I'll post that info. I'd much rather control the rear wheel with springs on the dampers than with some rubber of an unknown spring rate (and possibly a very high rate if the rubber has lost its resiliancy). cheers, Michael Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 14, 2008 Report Share Posted March 14, 2008 Thanks Michael. I do check them when I service the shockies, expecting them to fail at some stage, but they are still fine. I don't like the effect they have on spring rate but I have bigger issues with a couple of other bikes so will probably leave them alone till they give up the ghost. I think I read a TC thread on replacing those bushes with somethine else a few years ago - no it wasn't, it was in the story on the ITSA website about the KT that Bob Ginder worked his wand over. Photo attached. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 14, 2008 Author Report Share Posted March 14, 2008 David, I couldn't find anything at the ITSA website on that. Link? That bike doesn't look much different other than the upper rear damper mounts. Long rear travel (over 4" wheel movement) doesn't do me any good for an AHRMA Modern Classic bike. I may try and press the silentbloc bushings out tomorrow and see what that leaves me with. Maybe a brass bushing conversion won't be too much bother if Kawaski got the pivot tubes bored on the same center. Right now those silentblocs are looking pretty ugly. But getting the hubs off in the post comes first. When I do that I may run out to my storage space and pick up the Sherpa T front fork assy to bring home to ponder. cheers, Michael Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 14, 2008 Report Share Posted March 14, 2008 David, I couldn't find anything at the ITSA website on that. Link? I think you would need to be an ITSA member to see that write up on that bike. It is one in the "Bike of the Month" series. I just read the story again and there is nothing about work on the swingarm pivot after all. It may have been in a string on the TC forum where I read it. Here is the link to the KT story anyway for people who are ITSA members: https://itsa.clubexpress.com/content.aspx?p...module_id=11544 David Quote Link to comment Share on other sites More sharing options...
kt-milly Posted March 14, 2008 Report Share Posted March 14, 2008 Dear fellow train spotters!! At last, KT friends who wont get bored or get that glazed look when I talk about these bikes. I have the trick Kt mentioned in the earlier threads, and here's it's spec: I bought a 1000 mile, 1 owner from new KT about 4 years ago, and decided to try classic trials... just because I thought they looked great. I quite liked the bike, although heavy and sluggish, I thought I could improve it..... so... I bought a gollner stripped it, and built 1 good bike from all the nice bits. then had the geometry altered to a modern set up, including altering the rear shocks to a more laid down style, and fitting Falcon alloy shocks. Moved the pegs down and back. fitted Yam mono forks and yokes with the top yoke bar clamps cut off and moved forward. Yam YZ twin leading shoe brake set up, just as powerful as a disc, (cant understand why we never did that back in the day?). Now it handles superbly, although I might try a longer swing arm soon. Engine wise, I bought the last big bore kit from B&J Racing, which was incomplete but we got around it, so its 305cc, then had a reed valve installed to smooth things out at the bottom end.... a massive improvement! so was the keihn carb.... the internals on the exhaust side altered to match the new power characteristics. Used the gollner heavy flywheel and cover extension. calmed it down a little. Its still in development, and I will carry on with it, but as I was billy no mates on this bike, I bought a fantic 240...... now sporting many many mods, including a 307 engine conversion.... now I'm torn between the two as they both are great bikes to ride! Must say many thanks to the people that have helped with the midnight oil, especially Julian Wigg, Jon Bliss, Nigel Birkett, national treasures to any nut who wants to modify/improve any trial bike! Quote Link to comment Share on other sites More sharing options...
swooshdave Posted March 14, 2008 Report Share Posted March 14, 2008 Much bother if Kawaski got the pivot tubes bored on the same center. Right now those silentblocs are looking pretty ugly. If the pivots aren't perfect will you be able to put the bronze bushings in and ream them so they are centered? Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 14, 2008 Author Report Share Posted March 14, 2008 (edited) David, I joined up over at ITSA so I could see that. Thanks. KT-milly thanks for the info. How much lighter did the bike end up from stock after you went with the Gollner frame? I think last night I saw 26lbf on the scale for the frame with footpegs/brake lever/coil/spark box (no swing arm) with the swing arm being about 6.5lbf. I don't have my notes here in front of me but those should be pretty close numbers. Did the big bore cramp the transfer area at the case to the point where you had to add metal to the case to allow you to open them up? And might you have a nice high res photo that you could post of your bike from the side that shows all of it? Dave, one of the projects I've had sitting around is a table that will attach to the cross slide of my lathe so that I can attach things to it to align bore them. Until that is done I might be able to make a holder that would let me put the swing arm in a tool holder. That's something I'll look at today after I get the hubs shipped off. I think I've got a couple of tool blocks that accept a a 30mm tool shank. Maybe it will be the incentive to finally finish the boring table? I don't know if you're a tool guy but here's a photo of my lathe when it was delivered: cheers, Michael Edited March 14, 2008 by MichaelMoore Quote Link to comment Share on other sites More sharing options...
swooshdave Posted March 14, 2008 Report Share Posted March 14, 2008 (edited) Does anyone have a weight for a bare KT frame (with or without swingarm)? I'd like to compare that to a M92. I can't believe you stuffed that lathe into a SF garage. Did it cost anything to join ITSA? Edited March 14, 2008 by swooshdave Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 14, 2008 Author Report Share Posted March 14, 2008 34.5 lbf for the KT250 frame, coil and ignition box, swingarm and spindle, short rear brake stay arm, footpegs and brake pedal. I'll be interested to hear the Bultaco numbers. It was $25 for ITSA. That truck had a crane on the back of it. It also delivered my mill and picked up my manual mill to move it to the house of a friend who bought that and my bench lathe: We did get the mill stuck in the garage door until we took it off the skates and pinched it through. cheers, Michael Quote Link to comment Share on other sites More sharing options...
Guest majestyman340 Posted March 15, 2008 Report Share Posted March 15, 2008 34.5 lbf for the KT250 frame, coil and ignition box, swingarm and spindle, short rear brake stay arm, footpegs and brake pedal. I'll be interested to hear the Bultaco numbers.It was $25 for ITSA. That truck had a crane on the back of it. It also delivered my mill and picked up my manual mill to move it to the house of a friend who bought that and my bench lathe: We did get the mill stuck in the garage door until we took it off the skates and pinched it through. cheers, Michael Sorry Mike I was thinking you were wanting to build a top spec KT250.................here in the UK there are several experts able to make worthwhile changes on old twinshocks, and having been quoted only Quote Link to comment Share on other sites More sharing options...
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