Trials Australia Forums

Diff bore & stroke (77x65 vs 72x60)
Wider stud spacing
Wider transfers
Diff gear ratio for 2nd I think
Bigger flywheel
Larger cylinder casting (from Phantom I think)
Larger head to suit

(I had a 350 Super Pioneer)

Bingo to JC1, but how did they make the stroke longer? Does it have bigger crank wheels?

When they developed the Phantom MX engine for '74 they made the crank wheels larger dia (& larger width too if I recall correctly) to cope reliably with the extra power. They then used that crank on their other models too, including the Mk2 MAR 250 if I recall correctly (but not 100% sure). Anyway the larger dia crank enabled them to use a slightly longer stroke for the 350 (actually 302cc), but it still used the same wimpy rod & big-end bearing they'd been using for years, tho with the wider crank wheels they could use a longer big-end pin with more 'grip' from the crank (from the wider crank wheels) to help cope more reliably with the extra power/torque. They also used the bigger Phantom cylinder casting with the split fins on the 350 MAR & Super Pioneer models. Likewise the head.

Casper wrote:G'day Greg and David,
Hope you don't mind me jumping in on the discussion. I need to replace the air box/carby inlet hose on my TY 175 which is old , stiff and worn out (bit like me !) Any suggestions on a replacement. Can't seem to buy brand new Yamaha ones, so can any one suggest a hose from another model/brand car etc anything ??????????
Regards Neil Wilson
Denman Twin Shock Club member

Hi Casper I remember talking with you about TY250 hoses and how they can be made from toyota landcruiser coolant hoses, but the TY250 hose has a single bend that is easy to match on many coolant hoses. I had a close look at a TY175 hose last night and compared it with some car coolant hoses I found, and I could not see a hose that has a tight enough S bend to suit the TY175. I also looked at all the parts suppliers I knew of for TY parts and could not find anyone selling the original hoses or replicas of them. I suspect that there may be a car hose that would suit, but you would probably have to have a look amongst the stock of a well stocked supplier, to find what you want.
There always alternatives though, and if there was a hose that had a 180 degree bend of the right radius, it could be cut, turned and joined (with a short joiner) to produce an S bend.
Another option would be to find or make up a piece of steel or aluminium tubing that would fit to the TY air box, that allowed a straight piece of hose to be used between it and the carby.
Another option would be to look on eBay for someone selling one. I have seen those hoses for sale second hand on US eBay and UK eBay

David Lahey wrote:

Casper wrote:G'day Greg and David,
Hope you don't mind me jumping in on the discussion. I need to replace the air box/carby inlet hose on my TY 175 which is old , stiff and worn out (bit like me !) Any suggestions on a replacement. Can't seem to buy brand new Yamaha ones, so can any one suggest a hose from another model/brand car etc anything ??????????
Regards Neil Wilson
Denman Twin Shock Club member

Hi Casper I remember talking with you about TY250 hoses and how they can be made from toyota landcruiser coolant hoses, but the TY250 hose has a single bend that is easy to match on many coolant hoses. I had a close look at a TY175 hose last night and compared it with some car coolant hoses I found, and I could not see a hose that has a tight enough S bend to suit the TY175. I also looked at all the parts suppliers I knew of for TY parts and could not find anyone selling the original hoses or replicas of them. I suspect that there may be a car hose that would suit, but you would probably have to have a look amongst the stock of a well stocked supplier, to find what you want.
There always alternatives though, and if there was a hose that had a 180 degree bend of the right radius, it could be cut, turned and joined (with a short joiner) to produce an S bend.
Another option would be to find or make up a piece of steel or aluminium tubing that would fit to the TY air box, that allowed a straight piece of hose to be used between it and the carby.
Another option would be to look on eBay for someone selling one. I have seen those hoses for sale second hand on US eBay and UK eBay

Here's one and they reckon it is still soft
http://www.ebay.com.au/itm/3250-Yamaha- ... 53ff6753dc

David,
Thanks for the time put in and the generous information on the TY "Snorkel".
Regards Neil Wilson

Casper wrote:G'day Greg and David,
Hope you don't mind me jumping in on the discussion. I need to replace the air box/carby inlet hose on my TY 175 which is old , stiff and worn out (bit like me !) Any suggestions on a replacement. Can't seem to buy brand new Yamaha ones, so can any one suggest a hose from another model/brand car etc anything ??????????
Regards Neil Wilson
Denman Twin Shock Club member

Hi Neil,

Not a problem at all, anyone feel free to jump in anywhere, if you don't ask how can anyone help? About your airbox/carby inlet hose, has it just gone hard? If so, I have had a bit of success gently heating with a heatgun to soften them before fitting in situ, perhaps a hairdryer will be hot enough? Also with hoses that have holes, you can repair with black Sikaflex, inside and outside at the same time seems to work the best and check it periodically of course. The problem with TY175 airbox hoses is the first bend is a very tight radius which may make it hard to find a radiator hose to match?

As bikes get older, parts supply will dry up especially for popular models, but the good news is someone will reproduce parts eventually. As a side note most parts are now reproduced for Grey Ferguson tractors, even crankshafts.

Just sharing a progression photo of M A R:

Hi everyone,
Well Greg you like to tease us don't you. A partial photo!!!! At our last ride against each other we both rode KT's on some tough sections, but very enjoyable at Thunderbird Park. Of course I was concerned at times about damaging the nice paintwork on my KT.

David, I liked your acticle in the latest VMX magazine and Greg and my Juggernaut challenge at Easter time. My Italjet Scott 4 stroke is currently in hybernation for the winter....no I broke the kickstarter shaft and until I get time after doing the Ossa's, it will have to wait.

I have had some time to do a little on the Ossa "twins". That being an Mar 250 and Mar 350. Now isn't that a challenge, especially when 90 percent of the parts came to me completely pulled apart. These do really fit the bill of "Basket Cases".

As you have said David, somewhere in Australia, there has been a wizard casting some magic back into these motors and has done some superb machining.

Here are some progress photos for everyone and I have just sat the 350 motor cases in the frame to check there are no problems.

I spent a bit of time with the front wheels, but I am having trouble with the spacers on the axle. I can't get the wheel in the centre between the forks. These are the problems I face when bikes come in peices...... I also notice that both fork sets I am using are different. The lug on the bottom of the fork leg sticks out more on one set compared to the other. The lug locates on the brake backing plate.

Greg, I believe you rode my other on the weekend, so how about some action shots!!!!!!!

I thought that maybe while we are on the subject, it could be interesting to see how many people have out there looking at this post, and maybe they could show us a picture of their . Or maybe some old photos of Ossa MAR's being ridden back in their day.

They look fantastic Chippy. Can you do some close-up photos of the brake lug problem? Did you sort out the chain tensioner/brake rod issues?

OK see who can guess what year this photo was taken and who the rider was