I bought a new TTR250 2006 model and have taken it out about 2 times in the last 5 years, because all the crap going on at work, the missus hassling me to take her shopping and holidays, kids causing drama, mum visiting.. blar blar. Anyway have decided to tell everyone to nick off this year, and have booked a 3 day dirt bike tour of South West around Kirup, Pemberton etc..in November with West Coast Trail bike safaris run by John Staines. There is about 9 or 10 other blokes going and most of them have KTMs and 450 Suzuki etc. Previously fitted an aftermarket power pipe to the TTR and had it tuned by 5 Star Yamaha, but still not happy with performance, low end lugging, flat spots etc . I think the jetting is not right for the pipe and probably gum in the carby from sitting around so long. Anyway am biting the bullet and have a Thumper Racing 325 big bore kit coming from US and a 37mm Keihin FCR carby coming from Show and Go in Adelaide (my home town) of all places. Anyway read a few forums about these mods and a fair bit of info out there for uncorking the TTR. But of any readers have any tips then great to hear.. I did see one chap on this forum in Thailand doing wheelies on his TTR - must be in a lot better tune than mine.
mmmm...bit of a story.. some traps for young players here.. maybe better to send the donk to Thumper and get it back ready to go ? Will look into freight and turnaround. Doing it here - Considerations - Barrel - really a competent machine shop should be able to bore and press fit the 325 sleeve, then bore it to piston.. Will ask around about that.. Cases - going on the Steve Brian story, Im thinking not split the cases, but mount the assembled crank case upside down with some stout fabricated mountings welded to bench. Then make up a turning table with vertical boring bar, directly under engine. Center the boring bar, then rotate it (circling around the conrod with cutting tip pointing outwards) Skim out the necessary amount for the 325 barrel to fit. Cuttings fall away and not inside. That is what my minds eye is seeing. Will ask around some mates in the machining game to see if this is feasible. Any comments from reader welcome.. If not, probably send it to Thumper.. (sometimes one has to realise that great ideas coupled with the dream of great skill and finess, and the anticipation of great satisfaction,,,, in reality end up being a big headache..)
The cases will needed to be opened up to 87mm. It is a simple task for a machinist to do. They only need to bore through about ½” of material. I’m sorry I don’t have any drawings of the case procedure.
I asked if he knew if it was possible to machine the cases without splitting them. He replied:
I know a few customers that have used a Dremel to open the cases up but this is not the correct way. The cases should be split and engine components removed before boring.
I still have a residual oil leak through the cracks in my barrel and am considering sending over a spare barrel to Thumper Racing for them to sleeve and bore. I have already had my cases bored so I could just swap out the barrel and piston when they arrived back. Robin Webb did it this way and, after 1,000 miles, his 325 is oil tight and no "cracking".
Unless you have a spare engine, your TTR could be out of action for quite a while! If you sourced a spare barrel cheaply with a damaged bore (coz that won't matter) to send over to Thumper Racing, then you could keep your TTR running until the finished kit arrived and then strip your engine, bore the cases and put it all back together again. Worth a thought!
Brian, with the strip down and case splitting job. Was there much problem or simple fitting work? Im getting a manual and not bad at general mechanical work, have done a few engines when I was younger, but not recently and not so good when it comes to getting things off tapers, pressing etc.. Bike off the road is not really a problem for me. Only constraint is I would like it up and running by 19th November for the ride down South. Maybe strip the barrel off this weekend and get it air freighted to Thumper Monday. Then carefully dismantle the cases. Send them off for machining. (will need to get exact dimensions and tolerance off Thumper). Then take time to carefully re-assemble cases over following weeks. Then everything is ready when barrel returns for final assembly of top end. This is current thinking... Jon
I am pretty sure that I documented any difficulties I found but, to be honest, I would really try hard to find a way of masking off the bearings so that I didn't have to remove and replace them.
The original barrel/crankcase interface has a very large O ring type seal which I guess is to stop oil from the crankcase being forced up between the barrel and liner. It may be worth considering machining a groove in the crankcase to take such a seal.
Welcome to the forum, good choice of bike and i look forward to seeing your progress on your engine work, if it were me though I would be leaving the work till after your trip, the ttr as it is standard is a great reliable bike and you can enjoy your trip with no worries of any problems with the bike or break downs but once you start this work things may change and you would need to cover some mIles once done for running in/ fine tuning/ checking for any problems.
The best of look with your bike and your trip anyway and I am sure brian will keep you on the right tracks anyway!
Cheers Adam I think sound advice that I know I should take. But the momentum is gathering. 37mm Keihin FCR carby and exchange cylinder and 325 kit are in the air as we speak. Several mates have put our/their collective heads together and come up with a plan to machine the cases without disassembling. Again against all advice im hearing from out there including Thumper Racing. Anyway this week is week 11 on the count down to the big trip. Plan is to disassemble top end of motor this Sunday. Wait for 325 cylinder to arrive next week. Then attempt the crank case machining job. The guy doing it has a small shop with NC mill and will allow me to check everything he is doing. Once programmed we will do a dummy cut in a piece of scrap aluminium and measure before doing the crank case. The plan is to install a slither of stiff plastic between flywheels and case with a hole for the conrod to poke through. Then seal up with silicon. When machining commences vacuum the cutting as they are produced to reduce risk if silicon seal fails at any point. Bold plan, but thats the plan. We will take photos as it happens to share. Im expecting the motor to be ready for assembly in 3 to 4 weeks. Then the plan is to take the bike to a shop in Perth that has a dyno. They specialise in jetting motorbikes that have been modified. I think best just get it done and get the tuning right from day one. This should take no more than 2 weeks if I book it in ahead. This leaves me 5 to 6 weeks to test the bike and sort out any bugs before the trip. Keep you posted how it all goes. Jon
Gonna watch this one with great interest! Lots of pics would be good
Talking last night to the mother of a guy who fitted an Athena 144 kit to his YZ125, it appears that the cases need to be ground back to clear the bigger piston.
Against advice, he followed the tactic suggested on a forum which was to block the crankcase opening with a cut out aluminium drinks can sealed in place with Plastiscine which is apparently oil based. This is supposed to mean that any bits falling into the crankcase will dissolve - allegedly! The crankcase opening was then widened with a Dremel
Are you re-sleeving the barrel or are Thumper going to do that?
It will also be good to know what HP the 325 (actually I think it is 315cc if you do the calcs) puts out but, ideally, you should run your standard donk up on it before any work is done so that you have a marker....
Brian Thumper are sending me an exchange 325 cylinder. The deposit is $200 which is credited back to my card when my cylinder arrives at their plant. My bike has already got an after market exhaust fitted and Im pretty sure jetting is not right. It is fairly flaky and several flat spots at different throttle openings. It wouldnt be worth dynoing it in its current state. Happy to share the dyno results once 325 upgrade is finsihed and tuned. Jon