A forum for owners of Yamaha TTR250 trail and enduro bikes!

mossproof · Super Guru

350cc Big Bore Kit for the TTR250 - updates and gossip!

Shank · Newbie

A mate and I have one each on order.

We are waiting somewhat patiently here in South East Queensland for an updated ETA on the current batch.

I know, "you can't rush perfection!"

mossproof · Super Guru

Still waiting for the machinist cry

Thank you for your patience! He does know what he is doing, but is extraordinarily slow. Trying to find anyone willing to do it was damned hard the first time so I have been unwilling to go through it all again. As soon as they are done I will get them dispatched to Steve for distribution.

Shank · Newbie

I appreciate the response, thank you.

ttr steve · Super Guru

Everyone is keen to get on with their kits, but we have to be patient with the machinist, hopefully soon smile

IOWChris · Member

Very interested in a 350 kit, are there any left over from the last batch, or another batch on the way?

ttr steve · Super Guru

Chris . There may be one available soon. A guy called Dom paid a deposit, but he is not answering my recent emails for the lastt month. Will let you know soon.

Steve

IOWChris · Member

That would be perfect! Was expecting a long wait for one

IOWChris · Member

Thought I’d post here rather than start a new thread or continue my one about pulling the crank into the bearing

I’ve got my bottom end fully assembled now, and have noticed an issue. My casings had the breather on the case while my new casings have the blanking plug so must have had the breather up on the cam cover

At this point with cases assembled it seems very risky to try to remove that plug so had a bit of a panic until I saw covers with the breather attachment for sale on totallyttrs. I’m assuming I can just buy one of those and attach my breather to the cam cover?

mossproof · Super Guru

Yes Chris, by far the easiest option!
You will probably need to extend the breather pipe a bit, unless you can get one that matches the cover.
Pulling the blanking plug out would have required finding a suitable piece of tube to press into the hole as well.

IOWChris · Member

Awesome thanks Simon, found some fuel hose that should fit in the workshop

I’ll place another totallyttrs order then, just got one delivered today! Very lucky to have fast and reliable supply of parts for these old bikes

I’ll order a 140 jet as well as I see on the big bore jetting thread and this one you recommend 140 48 jets for your setup, mine is the same minus snorkel so seems a good start point

Got the top end all prepped today so hopefully fit it tomorrow

IOWChris · Member

Engine all dry fitted, bit of dremel action and it’s all fitting nicely

For sealing the base gasket is the loctite 574 used for the cases the right stuff?

mossproof · Super Guru

I think loctite 574 will do the job. Only needs a very fine smear.
What did you have to Dremmel?

IOWChris · Member

I picked up a tube of QX gasket sealant in the end, it’s the right stuff for the job and cost £4! Hopefully the baby goes down easily tonight and I can get it all fitted

Took a dremel to one of the fins to get a bit of clearance for the stater motor as it fitted but was butted up on it pretty hard. Also had to gently enlarge one of the upper dowel holes for the head a tiny amount as the dowel wouldn’t go in, made sure the dowels were smooth and tried them all in there but none of them would go in even with some persuasion. Not sure how that happens as I assume the machinist uses the same tool for all holes and the others were fine! Could be my first attempt at fitting it was a little skewed and caused a little deformation, in any case it only took a gentle run with my cheapo battery dremel so can’t have been much material

The barrel doesn’t perfectly slide down on the case dowels either but with a very gentle tap seats nicely so seems all good to fit, I expect there’s some variation in the cases and some variation in the barrels. Checked without the dowels and it goes down nicely so the case machining is perfect

-- Edited by IOWChris on Monday 16th of February 2026 01:57:50 PM

TTRfan · Super Guru

Excellent progress Chris and thanks for updating us! smile

Brian