Ty175 To 200

[ausy300pro]

Can anyone tell me if there is anyone doing the 200 conversion kit for the 175, also is it a worthwhile thing to do to a 175, I have had conflicting reports some say it's good others that it makes bike peaky and less tractable, I know it can depend on how well set up it is.

Help/pointers much appreciated.

[andy.t]

You can get the kits from HERE and if think you should be able to get one from HERE you will have to give this guy a call as they dont look like they are listed but he has done them in the past. A mate of mine has one fitted but I think you would have to be real keen to want one for that little extra.

Edited June 5, 2009 by Andy.T

[ausy300pro]

Thanks for reply Andy, I have already been in contact with craig from the majesty site, I have just bought my Majesty and it has a bit of piston slap anyway so rather than pay roughly

[ausy300pro]

Can anyone tell me of their experience with a 200 conversion, I need to know asap, have just bought a majesty and am sending barrel off tomorrow for exchange 200 barrel and piston, I am told (by someone with experience with ty,s) that the 200 kit can cause problems because of thin liner that sometimes cracks, I do want the extra cubes (and my 175 piston and barrel are worn) but dont want the thing to blow up or be unreliable.

Thanks for any help/opinions

[feetupfun]

I've been riding my 205cc TY175 since 2004. It is not the same conversion as John Cane or Craig Mawlem. It uses a piston made for big-boring the DT200/WR200 motor. It happens to have the right pin diameter and piston height to crown dimension that matches the TY175, so no barrel spacer or gudgeon pin bushes are needed.

I use a standard carby, standard front exhaust with WES rear muffler and standard airbox arrangement and standard port and ignition timing. The barrell was resleeved bigger using a second hand Suzuki GS1000 sleeve. The cylinder head retaining stud holes were welded up and redrilled 8mm and plain 8mm nuts used hold it together. This was to provide for the increased ID of the head gasket hole. The head was machined to suit the bigger bore diameter and to provide slightly higher compression ratio than standard. The crankcases were machined out to suit the OD of the bigger sleeve. The flywheel is standard.

The positives

It runs fine and has more torque at all RPM than standard but only as much as you might expect with the extra 30cc.

It is more responsive to throttle input (same flywheel and more power)

The negatives

It vibrates noticably (due to the increased mass of the bigger piston)

It stalls easier

It is easier to break the standard flimsy kickstart lever when starting it

The motor mount bolts have to be removed and motor inclined to provide clearance to get the barrell on or off the (longer) studs.

[andy.t]

Just a thought, the standard bore is 66mm which would give you 171cc and there are some 68mm pistons out there which would give you 181cc so your getting close to that 200cc.

[ausy300pro]

Thanks for replies,

First to feet up fun, that really is a lot of work to get it up to 205cc, I take it with using a Gs1000 liner you then have to machine in (somehow and I don't know how) all the ports, ok I suppose if you have the tools to do the job plus the knowledge and skill, I think the 200 kits I have been offered fit into a standard crankcase mouth so assume it's just a real big boring job and piston (which makes it expensive for what you get) this would then leave a very thin liner and compromise reliability.

I am thinking like you Andy T that I can just go up to maximum rebore size which will give roughly another 10cc and then fettle bike from there probably electronic ignition and some minor port work (Have you seen the mismatch between the carb manifold and the reed block ?) just clean up ports and tidy things like the reed block, I have some boysen reeds on the way, don't know if this will do owt, I would like to raise the compression a little as well so may get head skimmed as long as it does not ruin the squish band.

Any more TY tips for a new 175 mini majesty owner much appreciated.

[feetupfun]

If the sleeve fits the standard crankcase mouth, it will be less than 200cc. Mine has a 72.5mm bore, very thin sleeve and the studs are just touching the OD of the sleeve.

You don't machine the ports. You cut them by hand undersize before the sleeve is fitted, then enlarge them back to the right size with a porting tool to match the ports in the aluminium casting. That is the same with any new sleeve, big bore or standard.

Yes raise the compression, fit a good electronic ignition, and lighten the flywheel a bit. If you go up in compression much though, don't lighten the flywheel as my standard flywheel is now a bit on the light side with the higher compression.

You can machine the head for more compression without affecting the squish height by machining the squish area back as well as machining the sealing surface. Most people just run a very thin head gasket to get the compression up a bit.

Yes I would agree that if you want to retain full reliability, then retain the standard sleeve. My sleeve is scary thin, and I don't expect to get the life from it that I would expect with a standard motor.

[tony27]

When you talk about skimming the head to raise compression how much are you talking & does the timing need to be altered to suit?

[feetupfun]

When you talk about skimming the head to raise compression how much are you talking & does the timing need to be altered to suit?

If you are asking about mine, the squish area in the head on mine was machined to make the OD of the combustion chamber the same diameter as the bore. That change combined with the bigger piston displacement changes the compression ratio, so the sealing surface was machined to bring the compression back close to but slightly higher than standard. No I don't remember how much was machined off the sealing surface and it would probably not be much use knowing anyway unless someone was to do one exactly the same big-bore job.

No the timing works great at the standard setting but low RPM throttle response is more sensitive to the timing setting than before. I think an ignition with an advance curve would provide further benefits.

[ausy300pro]

Thanks for replies, I have been offered a 200 kit that fits into the standard crankcase mouth, I did a quick bit of calcualtion and I thought the same, it wont get up to a full 200 with the standard crankcase mouth, I know when shirty did the 200 he machined the crankcase mouth, that was not done for the fun of it, I will go with my plan of a +2mm overbore, all I need now is a supplier of a good quality piston, I thought I had found one but only to be told that the piston I was going to buy (for a DT175MX) was not the same as a TY175 piston, so the route I am going to go is the big bore, boysen reeds, skim head (I have also read that the DT175MX uses a thinner head gasket for more compression), and electronic ignition, I would then look to putting a 24mm flat slide OKO carb on in the near future, I am hoping this will be a good combination to keep or improve the bottom end at least as much as the mid and top end

[andy.t]

when you fit the Boyesen reeds change the pilot to a 27.5 for a start, could even go higher but will have to experiment, the miss match on the inlet can be improved with an rd350 inlet rubber which will also give you a point to connect a boost bottle, dump the old air box and make a new one with improved air flow.

[ausy300pro]

OK thanks for that Andy, is that a 350 LC or an air cooled inlet rubber (or either)

[andy.t]

OK thanks for that Andy, is that a 350 LC or an air cooled inlet rubber (or either)

the one i fitted was from a 350 lc but you will have to shave off a couple of bits of rubber that would have protruded into the reed valve, not a problem, just shave off with a Stanley blade.

[subanator]

Note the the LC350 inlet has the carb set central in the rubber, this puts the carb very close the exhaust, and would put heat into the carb. This could cause problems with tuning.

The original TY one you will note is offset to the left.

Changing the airbox is an eligibility issue as is not standard and would be considered a major component. I just used a better quality air filter and not over oil the filter for better breathing.