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XT 350 Top End
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Long story short, my 1993 TTR 250 had sprung an oil leak, it was oozing for ages, then suddenly something must have given way because I got home from a ride and oil was pouring from around the base gasket.

I proceeded to order a head and base gasket set. While changing the gaskets, I noticed the piston was ruined, well maybe not, but why not do it while in there? I then ordered the Wossner 263 piston kit from Brian here. I rebuilt the whole top end eventually and changed every gasket in that engine in the end. I could strip that engine with my eyes closed now. So, I had the bike rebored. Boy, did that piston make a difference. I can't tell if it is because I actually have some compression now, but it certainly gave the bike that pep I was looking for. I have done 2000KM's on that piston now. Seems to be going well. The bike no longer sounds like a lawn mower, so there's something.

Here's something I considered, while looking for parts that would fit my bike, whilst being cheaper, I noticed lots of XT350 engine parts looked very similar, I even have some gaskets and some other stuff off a 350 in my bike now. I was wondering if anyone has ever tried to fit the top end off an XT onto a TTR? The parts fisches make the engines look very similar, and I was wondering if it would make a cheaper option than the 325 American kit?

Adam



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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)



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I just checked the specs and it seems like both motors have the same stroke. I suppose the rest will be up to cam chain alignment.

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the 350 top.end fitted straight on early tt250s untill a change of the stud pattern .which as far as Iknow continued on with the ttr 250 .



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I thought maybe the studs may not align fully. I also considered the difference in cylinder-head design. Could lead to problems, or maybe the need to fabricate an engine mount.


http://pdn1.vnexttech.com/yam/mcy/1988/xt350u_uc/cylinder/assembly_files/11/1_1.png

http://pdn1.vnexttech.com/yam/mcy/2000/ttr250m_mc/cylinder_head/assembly_files/10/1_1.png

They are very similar. I think if the gudgeon pin fit the piston, which I suppose it would, and the piston could pass through the crankcase unrestricted, I don't see why it couldn't be made to fit.

You would also need to consider the twin header pipe design of the 350. If I could ever pick up an old 350 for cheap, even not running, I would like to give it a go.



-- Edited by Fladdem on Tuesday 4th of March 2014 09:29:42 PM

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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)



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ttboof wrote:

the 350 top.end fitted straight on early tt250s untill a change of the stud pattern .which as far as Iknow continued on with the ttr 250 .


 Mmmmmmm Having an early RAID that sounds interesting, I assume that the valves on the 350 heads are bigger?

It'll need to wait till I've sorted some bigger valve heads for my monster unless one happens to crop up in the mean time.



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Anyone ever confirm the viability of a top end swap?

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Moo


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I very much doubt it would fit, otherwise the other guys would have gone to the trouble of casting a new 350 barrel



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Malcolm, Northamptonshire. West Anglia TRF 1996 TTR 250 Raid



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Not ttr 

But my TT 250 cracked between the spark plug and exhaust valves . a srx 250 road bike head went straight on slightly higher compression a bit better down low grunt 



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I considered this early on to achieve the e start 350. TTR250 crankcases have a different bolt pattern and the mating surface for the bottom gasket is not the right shape. Other differences: gudgeon pins are different, conrod is different length... I even thought about filling the barrel/head bolt holes and building up the base gasket surface with ally weld then machining to suit the old 350 barrel, then you have to sort out cam chain length and timing, try and fit 2 carbs where there's barely room for 1, make up exhaust mods etc... Sorry folks, there's no easy way
Ride safe, and dream,
Simon.

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Sounds like a fun project..

 

I wouldn't run two carbs, I'd machine an adapter and run a single larger bore carb.  Timing.. an adjustable Cam sprocket set could easily be used/made to since timing for chain length..

How about the 350 head on the stock jug with a 325 kit?  Would give you bigger ports, valves and better suited camshafts!  Probably would be allot easier to machine the head for offset bolts than the case...?

 

Fun to internet engineer..hahaha

 

Chris



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