ty 250 mono aftermarket parts

[Ferretflasher]

After having checked both bikes running, I have to assume that #2 vibrates more than #1 MA bike. Spoke to Nigel but he can only supply 70mm piston with large crescent cut-away in bottom skirt by Wiseco. Now I know from my Fantic days that these pistons wear much quicker than normal pistons with the reduced skirt as they dont like the piston thrust to the front/back direction and so wear rapidly and soon become noisy. Nigel would not admit to such but did admit that they change pistons as necessary .... ie when they become noisy !!! So its now a case of using Twinshock piston or ANOther with the 2 windows in a full skirt that resists those thrust forces much better.
Anyway it now looks like a standard 70mm DT 250 piston is likely choice and shall get one measured up before I commit. Another carb obtained and 2 more in the pipeline so I can find a carb that works?? The current carb appears to fire loads of fuel in and I suspect leaks fuel past the needle jet and air past the throttle slide. The plug is always wet no matter what I do and lowering the needle makes it pink even worse. The over-run is chronic .... but once pulling ... it does pull very well .... its just very poor picking up on the bottom end.... and then takes ages to get back to idle .... banging and pinking as it goes.

Looking at entry list for this weekend (30 Oct) Hillsbro Classic Rd (in UK) has Dan Thorpe on Hamilton Yam Mono ..... and so I shall predict another crushing victory (that's the whole overall trial not just C class) for the Mono in Dans hands. Second in C class may be Mr Hankin (Beta) and 3rd Mr Ruscoe (GG)....?

Anyway time to get m #1 mono fettled, new IRC on rear, drain carb bowl, clean throttle tube ... thats about it !

[FM350]

Really does sound like you are having a bit of a nightmare, and I think you need to either think about spending some money and getting one of the bikes sorted properly, or get sell both and buy something more competitive with the money?

I wouldnt place too much importance on the results of any Hillsborough event, as the marks lost in actuality seem to differ markedly from those appearing in the "resuilts"...................lol

[Ferretflasher]

Nope !!! ....#1 bike Mick Andrews engine runs fine, its my serious bike I compete on. Its the #2 bike that don't run 100%, its one I am experimenting with to find out what I can and can't do to an already bloomin good bike. Once I have a good carb or 3 to play with (and I dodnt want to swap it with #1 bike) then I shall get it sorted

If you are implying that Hillsbro riders receive preferential treatment ........ surely not ............??? No OK so its always Darren W & Dave K at the rear but they do the donkey work so why not. Still a good impressive route especially Ughill sections.

Met a gentleman last week with about 9 TY red frame bikes and 2 pinky's, all working all ridden, laid up in his house and about 15 in bits in a massive chicken shed round the back, plus Fantics and Evos and a 4RT, impressive hoard !!!! So impressed I bought 1/2 a Pinky, set up my own breeding program.

[FM350]

I guess if its one of Micks motors its likely to be ok.........If it runs well then why not just copy whats been done to it, rather than trying other things which may or may not work?

Got the impression the marking was a bit dodgy at Hillbro last year, and so did Mike Rapley who commented on it in one of his TC pieces! Seems a real shame this sort of thing seems to go on, as it creates an awful lot of bad feeling, especially from those who might have had a very long journey to compete, and lose out due to cheating.

[Ferretflasher]

Thats the problem ... I cannot find those pistons ..... nobody does them AFAIK !! Anyway been talking to Dave Thorpe and he should know .... the piston to use IS indeed a DT MX piston with the crescent cut-out in the rear skirt. Looks like I need to eat a large slice of humble pie now because that what Thorpe'y, Birks and Mr Koch all say that's what to use !!!! So looks like I need to obtain a 70mm MX piston from Mr Birkett asap. The method to use is bore the cylinder so it just wont fit the piston and then hone it until it "just" fits in, that way the hone will wear a wee bit and give it the ideal clearance. Davids had his in the Hamilton bike for about 20 years and according to Dave, it needs to rattle a tiny bit .. that way it wont nip up while ever its rattling !!! So good enough for me !!
Now Mr Scarlett tells that his later TY monos where given a chrome bore by John S Senior in an effort to stop the rapid wear and once fitted with a good piston in a chrome bore, these would last ages. This was done to all the Shirt bikes eventually. OK those Shirt bikes were likely to be given some real stick but he does state that they were sorted once done. He also tells that he still has his ex-works JCM bike at home and might even consider rebuilding it do next years C class ACU rounds.Dont know if that will actually happen but would be good to see Tony and Dan on those old bikes again. Anyway dont yet know if Langcourts can do chrome or Nikasil coating onto a cast iron liner, shall enquire next week. It may well be that Shirty fitted an alloy liner and had that plated. Anyway its purely academic at the moment because thats a bit too exotic for my budget.

Anyway blooming good trial I thought and its interesting to watch Dan ride the Hamilton mono, very smooth with a nice fluid pace with no hesitation but thats why he wins everything in sight.

Must stop using Anyway at the start of a sentence ...........

[FM350]

A DT MX is a 250cc trail bike, and I know the pistons from these do not have the half moon cutaway, which I guess would be the case on an MX motor? The main reason I think the TY motors often rattle is down to almost all of the thrust face of the cylinder being taken up by ports, which means the cast iron liner isnt that robust, and will certainly lead to distortion when the motors heats up. If you are using an MX type piston with most of the thrust face cut away, this will add to the problems, and make rattling more likely.

I would think the solution to this problem is to look into fitting the cylinder from a TY250 twinshock, which has much more sensible porting, and can be made to work extremely well in 340cc form. Wonder what you think of the Chris Koch TY......I think this is probably the very best of the TY monos, and wonder how it compares to your ex MA bike?

[Ferretflasher]

Agreed, everything is telling me that the crescent cut-away will lead to the piston rattle (Fantic's did so) and I know the thrust forces cannot be supported by a skinny non existent skirt but the consensus of opinion is that this is what was found to be best. I may well decide to use a normal DT piston with those 2 window in the skirt but open up the windows to the same size as the inlet port while still retaining the solid skirt. Even standard Mono pistons wear most on that inlet side. I have taken out a piston from a standard bike that had some 0.8mm wear and it was all centred on the rear (inlet part) of the piston. I shall take another look at my #2 bike and look to open up those 2 windows as much as possible AND give it a slight crescent while I am at it but I think the skirt must not be totally removed. Shall pick Nigels brains again this week before I commit.
One thing I notice about Chris's bike is that it dont rev very high, its all bottom end the way he rides it. That massive exhaust header pipe and tiny silencer means it can pull 3rd quite easy rather that scream it in second. Its an effective bike but it must take a while to get used to it. Would hav e blagged a ride today but he was packed up when I finished back at van. It does pop and bang though when cold BUT it dont rattle !!!

[FM350]

Cutting away the thrust face wont make a scrap of difference to the performance of a trials bike, but it will reduce piston life by around 75% and mean rattling is going to occur pretty quickly. The same goes for opening up the windows............another complete waste of time, and especially so on the TY motors, which seem to have port volumes which are much too big, that results in slow gas speeds at lower rpm, and sluggish performance.

On motors like the TY Mono which seems to use a cylinder with slightly modified MX type porting, where the thrust face is almost all taken up by ports, piston wear is going to be far greater than a cylinder specifically designed for trials, and pistons will need to be replaced quite regularly to prevent rattling. I would think a good quality forged piston, designed specifically for these bikes would help a great deal, but not sure anyone would want to pay for parts such as these?

Chris's bike uses a full skirt DT piston if its still the same as when Jon built the motor, and while it handles very well indeed the performance of the motor is not comparable to a well built piston port Fantic, and even further away from a good reed valve bike such as Phils or Dave Pyes. Looks like Chris has won the Normandales this year though, which is good as he has been trying a long time..........

[Ferretflasher]

Hillsbrough results in and it looks like expected ..... Dan all clean on 0 (1987 Yam Mono) with Darren second (2011 GG) on 2 !!
Dont quite know what happened to round 9 results (Sutton Rose Bowl) looks like ACU has dropped them, cost me a podium finish

[Ferretflasher]

Right here are the findings I have relating to suitable pistons to fit 70mm bores (if you need to bore out bigger than +0.50mm), this is in addition to the 70mm crescent-cutout skirt forged items (Wiseco YZ250) items that Birkett sells.
DT250 pistons will fit and do the job but tend to be heavier cast pistons of about 1968 > 1971 vintage ( the very first ones are single ring types and should be avoided) dont use those items # 214-11631-01-00 as these have the Keystone ring while 438-11631-01-96 tend to have a Dykes type ring (L-shaped) but DT pistons 2N6-11631-00-96 and 1M1-11631-00-96 & 1M1-11631-01-96 are all suitable to use. DT250 pistons have 2 round "windows" in rear piston skirt. DT piston is 4mm shorter as the DT stroke is only 64mm not 68mm as the TY mono.

IT250 pistons are the later and more suitable piston to use and basically follow thus 1W5-11631-01-00 = 1977/1978, 2X7-11631-00-96 & 2X7-11631-01-00 = 1979/1980 and 2X7-11631-00-96 also fit the bill. IT250 pistons have 2 bigger "ovoid" windows for want of a better word for a shape that is oval and rectangular and un-equal in shape in the piston skirt ..... trapezoidal sounds like the word Im after but one side is bigger than other ???? Dunno !! IT piston is 4mm shorter as the IT stroke is only 64mm not 68mm as the TY mono.

My experience is to avoid pattern pistons and go for genuine Yamaha, the metal composition is better and they last longer. Finally the barrel base might have to be reduced by 1.75mm if using a DT or IT piston and omit the copper head gasket (1.75mm) thus giving you back some squish of 3.5mm!

Piston rings to suit each piston begin with the same format # but are basically ***-11631-** !!!

Question, could a cut down oversize ring fit a smaller bore provided the ring gap was increased or would the extra outward pressure cause rapid cylinder wear??