XT 400 Expansion

[Brian d marge]

The president of Aria helmets ( on cloud nine that one ) has a triumph triple , and an SRX400 with a 600 topend, no I didnt do the conversion it was before my time , but I did pick the bike up ,,after the rod snapped ,,,due to fatigue

IMHO the 400 rod is not strong enough ,,,, ( I wasnt in a position to verify 100 percent , as all I saw was rod sticking out of cylinder ..confirming it wasnt my work that caused the breakdown WHEWWW

I would check the loading to be sure before attempting to go big bore ,,just to be safe


Stephen

Swappsies ..is how I run my MX bikes ,,,the racers chuck out some good stuff!!!

[Motu]

Yes the rod does worry me,and after seeing the '94 rod even more so.The SRX rod was only a bit bigger than the 400 rod,but the later model rod is a lot beefier all over.So I'll bring the comp down some more,now I have a crank I can build up another bottom end.

[Motu]

Braaaap...pop,bang...braaap!

I ran the motor today,still lots to do,but I'm impatient and just had to fire it up.It took a fair bit of work to get it fired up,pops and bangs,short runs,but just wouldn't catch and settle down...maybe because the carbs have been dry for a year.It seems to run pretty well,I won't really know until I get the muffler and airbox on,but for an open pipe and carbs it seemed fine.

Then it got an oil leak...I thought it was from the crankcase join and became suicidaly depressed.Then I did a couple of WoF's,failed them on some petty little faults,had arguments with the customers - and after spoiling someone elses day I felt a lot better,and had another look.It was blowing out from under the starter and thought it might be a split breather pipe,so fixed that,but it still sprayed oil.Then I found it - coming out of a 6mm case screw hole,looks like I missed one.Behind the outer starter cover plate I found the hole with no screw - it was inline with one of the cover screw holes and I asumed that the bolt would go through into the inner case....not so it appears.So I fixed that tonight.

Too many interuptions in my assembly - I really hate that,I prefer to put a motor together all at once.I had all the components on a new tool trolley,next to it a new 15 litre parts washer - I could just walk out of my office and do a bit here and a bit there...which is not good.You need to get it right,and put your cases together without being disturbed,so I had to do that tricky stuff after work with the doors closed and no interuptions.I had to do the same putting the engine in the frame,behind closed doors.With the bike just outside my office,I couldn't find the time to work on it,one day just fitting the inlet stubbs.You'd think the boss could organise things better don't you?

I dunno about the jetting,but had a break through anyway.The 400 has a 108 primary and 96 seconary....the 600 a 130 primary and a 104 seconary,so I was going to have the jets drilled to a midway point.Then I thought I might check the SRX jets - and stuck gold,maybe.The SRX has a 120 primary and 100 seconary,near as dammit half way between.I'll make a desicion about low speed jets and needles when I ride it,but they seem almost ok,with a little spit back - that should go with the airbox and muffler.The needles have already been lifted,I did that when I fitted the Superttrap....but I'll run the standard exhaust this time.

I'll get some race fuel tomorrow and finish the bike during the week - it'll take that long to fit the airbox,prick of a thing.Gunno go riding on saturday!

[MacD]

How's the 400/600 conversion going Motu? This thread about an SRX400 reminded me to check what was happening here.

[juxsta]

Oh dear,what I was hoping wouldn't happen,did happen - the cranks are different!

I was put off a little as I have the factory XT manual,it shows engine strip and rebuild with photos and exploded drawings,and with the SRX crank in my hands they looked the same - but now I realise they must of been using a non electric start model for the photos,and only putting in electric start stuff when appropriate.Later in the manual under Alt and electric start I see the correct crank,but I didn't look there eh? Wish I had of known,or knew somebody who knew,I could of spent these 6 mths rebuilding the SRX and just done a swap,now I have TWO motors apart! Trouble is with Yamaha you can't buy a gasket set,you have to get each gasket,seal,Oring seperatly,what a pain!

I have the 550 manual but some parts are definitely different to the 400. E.g Carburetors
If you had a PDF version i would sure appreciate a link. My Model is 5Y7