XT 400 Expansion

[Motu]

My XT 400 is getting a revamp - I thought I might let you follow the pitfalls that I might encounter along the way.The XT400E Artesia is just a small bore XT600E,the same as the SRX400 to the SRX600,exactly the same bike,just downsized for tax purposes in Japan.The 400 is ok for what I need,it can handle the easy 4x4 tracks I use it on,it's actualy great on gravel - being underpowered I can give it heaps and just ride it flat,like an XR200,I don't have to control wheelspin.On the open road it can sit on 100 to 120 all day,but keeping it there can be a pain on hills and in wind,and passing is a very well planned event.With the loss of the XLV750 the bike cries out to be a 600....

Enter White Trash - all hail Jimmy the gigantic,the bringer of gifts to the helpless and needy.When flicking off his SRX600 track bike,he tossed a spare engine my way,it took a bit of getting to me,but the motor arrived and my XS1 left in the same vehicle - us bikers is good people eh?

So,the Yamaha single family...the learning curve begins.XT,TT,SRX,600cc,400cc...all the same,all different.The TT is the off road racer,lighter,more power,no electric start and a nikasil bore,nice if I could get one.XT is the trail bike,with electric start on the XT600E from about 1988?.SRX is the cafe racer,no electric start (ok,so late models have one,I know) and a tacho.Now a funny thing - XT,TT and late SRX are 595cc with a 95mm bore,but the first SRX600 had a 96mm bore and was marked 608cc on the barrel.The 400s have a smaller bore (85 I think) and shorter stroke,everything else appears the same,I think even the carbs are the same,same casting anyway.Apparently the SRX600 has the XT400 gearbox,I haven't checked ratios,but I think the XT400 would have a closer ratio box,so gets used on the street bike.The SRX has a weaker top end,weaker rod,barrel,smaller valves and a different stud spacing on the head,but the barrels will bolt on.Also the swingarm mounts through the crankcase on the XT and has a bigger hole.

What I intend to do is put the SRX600 crank and top end on my 400cc cases,that way I can keep the electric start,fit a kickstart as well and just generaly keep a later model bottom end.The crankcase mouth will need to be bored to take the bigger barrel,no biggie,but I hope(fingers crossed) that we will have a bolt on job.

I have stripped the SRX and found my first problem - a 97mm Wiseco piston - smashed! The crank is in great shape.To go up to a 98mm piston means the compression goes up to 10.2:1,not what I want to put on the weaker SRX rod - but we hone and measure the bore - only a thou wear and no marks at all,so I can keep to 97mm...that's 621cc.I can't get a Wiseco,well I can,but it needs to be imported,so settle for a ProX job.This looks bigger than the cut down forged Wiseco piston,but is the same pattern as original,so should be fine.As to why the Wiseco piston failed? It has been running for some time like that by the wear pattern,and it's the non thrust side that is missing(found some of it) - my guess is that the balance shaft has been incorrectly timed and knocked the skirt,either snapping it off,or cracking it and failing later on,but of course I never thought to check the balance weight timing before I ripped it apart.

The rest of the job will have to wait until I can take the XT400 off the road,either when I get another bike,or wait till winter.Here's a picture of the Wiseco and ProX pistons next to the barrel.

[Bonez]

Looking fwd to more installments.

[Motu]

Looks like I had to wait for winter - I didn't expect to buy a house Xmas Eve and spend 6 mths doing it up and shifting.

So out came the 400 motor and I'm pulling it down,I've got the top end off and got some photos to show you the difference in bore size.Same castings,but the 92 XT has some differences to the old SRX,a different stud spacing on the head and longer head bolts - as I mentioned the later XTs were stronger in the top end.The inside of the 400 is spotlessly clean,which is a good sign,looks much better than the 60,000km it's done,confirming that these things will last forever.

The valves are smaller in the 400,but port sizes the same,carbs the same size,camshaft identical - no wonder it would hardly run with the airbox opened up,they just restricted the air intake at the filter.

I'm stuck getting the flywheel off,it doesn't want to move and I'm leaving it with pressure on while I give it stern looks and mutter threats about heat and hammers - if it doesn't do as I command tomorrow I will have a quiet word with it alone....just the 2 of us and some nasty tools.My main worry is if the cranks will be the same.

[Artifice]

considering the effort they didnt go to to make the carbs different, i doubt they made the casings any different either. sure the 600 crank probably needs another 10mm or so of space and the counterweight will probably be thicker. on second thoughts i rekon they designed the 600 and then just restricted it down for the 400. maybe the 400s counterweight is the same only got some of its guts missing. flatmate did a similar job on his klr600-650. needed to put in a spacer at the bottom of the head to make room for the longer travel. as you have a 600 head i guess its long enough allready. just measure it first ay.

good luck with the build. sounds like a cool project.

[Motu]

The SRX is an 86,the later models had wider stud spacings and you can see an extra bolt hole in the chain tunnel....so the heads won't interchange,but the whole top end will.The balance shaft will be a different weight,that's no worry - but the SRX is kick start,the XT has electric...and a different flywheel with start gear etc,they look the same in the parts book....and I hope in real life too.

[Wellyman]

Good luck Motu. The pistons well the look intresting to say the least. Goo luck with your rebuild and keep us posted. I think my CRF is probaly due for a bit of an overhaul.

[Sensei]

Coul you not put the whole SRX600 into ya XT ?? Did a 640 kit into my
1990 TT600 breath taking power .

[Motu]

I want the original cases and electric start,putting the SRX crank in XT cases is easier than adapting the SRX to electric start.The bigger bore kits have higher compression,not what I want...although I think the 101mm piston is standard comp.

[Motu]

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

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!

[Motu]

I have a new plan,deep in the shit,the fertility of my brain plumbs new depths.I'm gunna make an XT500!

An XT600 is 95mm x 87mm,an SRX 600 is 96mm x 87mm,an XT400E is 87mm x 67.2mm....I have a 97mm piston.I'm going to use my 67.2mm crank,and just put the 97mm top end on,making a short stroke 97 x 67.2 motor - Mr Skid and I worked it out to 495cc,pretty close huh?

Now,the complications.....the cases will still need machining for the bigger sleeve,so I still have to strip the XT400,can't just slap the top end on.It will lower the compression with the shorter stroke...is this a bad thing? enough to notice?....I will do some measurements.I could put the big sleeve into my 400 barrel,and use the 400 head,same size ports,but smaller valves,but this will raise the compression....by how much? more calc required.A jetting nightmare with carburettors with unavailable jets.

I like the idea,no big cubes is a let down,but a short stroke big bore is an interesting idea....grist for the mill in my brain....

[Sensei]

:Punk: At least it's only 1 piston Motu

[sels1]

When you first started this thread I owned a XT400, so I watched with interest.....but then I couldnt wait for the next installment so went n bought the F650 :laugh: Good luck with the project!

[Mr Skid]

I have a new plan,deep in the shit,the fertility of my brain plumbs new depths.I'm gunna make an XT500!

An XT600 is 95mm x 87mm,an SRX 600 is 96mm x 87mm,an XT400E is 87mm x 67.2mm....I have a 97mm piston.I'm going to use my 67.2mm crank,and just put the 97mm top end on,making a short stroke 97 x 67.2 motor - Mr Skid and I worked it out to 495cc,pretty close huh?

Now,the complications.....the cases will still need machining for the bigger sleeve,so I still have to strip the XT400,can't just slap the top end on.It will lower the compression with the shorter stroke...is this a bad thing? enough to notice?....I will do some measurements.I could put the big sleeve into my 400 barrel,and use the 400 head,same size ports,but smaller valves,but this will raise the compression....by how much? more calc required.A jetting nightmare with carburettors with unavailable jets.

I like the idea,no big cubes is a let down,but a short stroke big bore is an interesting idea....grist for the mill in my brain....
I've worked out the formula for maximum piston speed that i was telling you about - should be able to model the piston's travel on a sine wave, and differentiate to work out the redline based on the stroke. That doesn't take into account whether you'd get valve float or something other nasty at high revs.

The XT tacho only goes to 9k rpm though - you might need to fit an Apexi monsta tacho to the Renthals..

As for jetting I reckon it's going to be enough of a mutant to justify dumping the YDIS carbs.. Didn't one of the SRX sites suggest that the carbs from a gpx250 would bolt up happily to the manifolds?

[sAsLEX]

the formula for maximum piston speed that i was telling you about - should be able to model the piston's travel on a sine wave,

blah blah I do Science.....................



I reckon it should be a cosine wave!!!!!!!!!!





But in all soberr(splelt this wauy when sober!!(_ ) it is cool to see peopleple fiddling!

[Mr Skid]

blah blah I do Science.....................



I reckon it should be a cosine wave!!!!!!!!!!





But in all soberr(splelt this wauy when sober!!(_ ) it is cool to see peopleple fiddling!I'd have far more faith in your mathematics ability than mine (though not right now, from your spelling).
I enjoy maths, I'm just not terribly good at it

[Motu]

I've worked out that using the 600 top end will give me a 7:1 compression ratio...not really the hot set up for the 21st century,but I could run any flamable fluid no worries.The 400 top end will give me an 11:1 ratio,a bit borderline,but I think it could take it.But I can relieve the head a bit and bring it down to say 10:1,the only down side is the small valves,but I think we can still flow enough for 7000rpm.

My engine reconditioner is not too keen on the sleeve swap,he reckons it would be cheaper to weld the combustion chamber to get the compression up and get the bigger valves than swap sleeves.Apparently it's a shit of a job machining the barrel to the bigger size,putting the step in the top is the hardest part he says.But I want the stronger castings and better stud spacings of the later top end,so we are doing it my way....next we gotta hope the barrel casting is the same and we have enough meat for the rebore....

[MacD]

How's it all going? I used to own an earlier kick-start only SRX600 (608cc version) and now have an electric-start monoshock SRX400. Reading up on the differences between the XT and SRX versions of the engines I was surprised that Yamaha bothered to make as many changes as they did. Maybe one day I'll look at putting an XT600E engine in the SRX? Apart from the rear engine mount difference, the driveshaft sprocket supposedly has a different offset on the XT engine.

[Motu]

Still statis quo - I had planned this over winter and I'd have 2 bikes for summer,but now the DT230 is my road bike....and I'm kinda enjoying that,but it was supposed to be my off road bike.Oh well,I just go with the flow and enjoy what I've got,every bike is a good ride I reckon.

I'm not pushing my engine man,we have a symbiotic relationship - I give him work,and he keeps my work on track.If I lean on him he might get a bit riled.We have a Jag thing going at the moment - I had a 4.2 lying around my place for a year,he's had it for a couple of years,and now it's all done....and the cars here.A MkII,and as well as taking the 3.4 out and fitting the 4.2,we are converting it to left hand drive for export to LA,with an electric rack and pinion.A freaking nightmare I don't need with a month to Xmas.There are still little things to do to the 4.2 now we have both out....when this is finished I'm going to demand my bits be done.

[Motu]

I got the barrel back a week or so before Xmas,and it's turned out lookin good.We were a bit worried if the casting didn't have the same wall thickness to take the bigger sleeve,but I was sure they were the same casting.So now I have to strip the bottom end so the crankcase mouth can be machined out for the bigger sleeve.I have relieved the head a bit to unmask the valves,I'll do a trial assembly and measure compression volume with a burret and work my way down to say 10:1.Still a long way to go.

[Motu]

One step forward,another back....I just feel I'm going nowhere.

I stripped the 400 cases and was pleased to see everything in top order there,the bearings are perfect and not a mark on any of the gears,makes a change for these motors.But it's all 600 internals with a 400 top end,so not suprising,even at 60,000km.

So the cases have been machined and I was getting ready for a trial assembly when I find out the gudgeon pins are a differnt diameter!! Ahhh! How the hell did I miss that? Both pistons have been sitting side by side on my desk for months,but I didn't notice that the 400 is 20mm,the 97mm piston 22mm,the pin is also shorter.There are no standard bushes that size,so I'll have to get some made,plus spacers on the ends,maybe make the bushes flanged to take them out to the circlip groove.I don't think my engine man will be too happy with fussy work like that,I'll get a mate to make them....this guy was around a few weeks ago and said why didn't I stroke the old flywheels...just weld up the crankpin hole and redrill further out,he does it to Harleys enough.Well too bloody late,we are on a different plan!

I've also just weighed the pistons....

87mm piston - 337g

97mm ProX - 431g

97mm WISECO - 331g

So the piston I am fitting will be 100g heavier than stock,but I don't think it will make that much difference,seeing as the WISECO is 100g lighter than a stock 600cc piston and used as a replacement.The rod eye is smaller in dia,but with the shorter stroke piston speeds will be lower and piston reversal loads less.I've been weighing a few things and a Panasonic D cell battery is 100g,hmmmm,pity I couldn't get a WISECO piston as it's almost the exact weight of the 87mm 400 piston.

[cheese]

that is some big diference, but i think you'll be fine with an extra 100g in the piston.

are you getting sick of that bike yet? sounds like a bit of a mission! need to put some pictures up.

[Motu]

I got the piston back tonight,piston bushed to 20mm,with a couple of alloy spacers out to the circlip groove,a nice job.Cost me a WoF check (he failed,heh,heh) and a couple of BSA sausage mufflers he spotted under a bench.We've known each other for over 35 years,and that's how deals were done in those days - good to see we haven't lost the skills....

I popped the crank in the cases and did a quick dummy up to see how it looked - it doesn't look short stroke at all,I see inside all sorts of motors and this 97mm x 67mm looks quite normal.I was worried about deck height/piston protrusion,and it sits 0.6mm above the barrel,and the used head gasket is 0.9mm,so pretty tight squish clearance,and with the small combustion chamber more squish area than normal.I might do a plastcene check .

So,progess getting made,now I'll have to start ordering parts,gaskets,timing chains etc.

[cheese]

get some pictures of this beast in progress for us!

[Motu]

Dummied up today and playing with a burrett I get 10.36:1...sounds perfect to me.

[Motu]

Did a double check on the compression ratio,I've had 2 at 10.37:1 and one 10.36:1,so 10.37:1 it is.My squish is 0.75mm,about 30 thou which is perfect.There is a lot of squish on this motor with a 400 head on the 600 bore,so need as little as possible to control detonation,without getting into clearance problems...fingers crossed.With a little more cleaning up on the head compression may come down to around 10.25:1,about where I want it.

Now I just have to accumulate gaskets,seals and cam chain - all seperate items on a Yamaha,I hope to have some luck on the internet.

[Motu]

Oh boy,my head is spinning! A few developments today...

I ordered a gasket set the first week of march from Coyote Motorsports,they plucked my money on the 8th,and I have had no contact with them despite several emails,apart from ''Have you got it yet?'' So I have given up and started to put it together using gaskets from Red Baron...and as I expected it's been a bloody hassle.Today I get an email from Coyote saying DHL have been repeatedly trying to deliver it,if I don't pick it up it will be returned to the US with no refund.So I ring DHL to track it - they find it has been addressed to Wellington! Um,no Mt Roskill there! So I should see the gaskets tomorrow.They had an issue with the ZIP code...but we don't have them,I gave them my area code - the new ZIP code system should prevent such hic ups in the future.

A couple of months ago a guy came in looking for a fuse,and said ''What are you doing with the XT motor?' Ah,someone who can tell and XT motor lying in parts,must know them inside out.It appears he has the same problems as me - in reverse! He has an '86 Tenerie with the dreaded 5th gear problem,so picked up a '94 bottom end and used it's gearbox.But he can't use any of the other parts,as it's electric start...and he has the crank! So we do a deal,I get all his '94 parts and I give him my Tenerie tank,he brings in the cases today,and I give him my SRX crank in exchange for a damaged late model head.The con rod is not in good nick (the reason for the swaps is everything is useless to each of us) But I think I can find the right people to restore the rod and give me an 84mm crank.Next interesting thing is the '94 cases have the updated external oil feed to the gearbox,and a higher capacity oil pump...now that'd be nice.

So now what do I do? Fart around trying to make it a 600cc,or be impatient and slap the 500cc together.I think I'll put it together as the 500cc,as I'm kinda interested to see how it goes,then I'll have time to work on the 600cc crank and cyl head,then pop everything into the '94 cases at as later date...this thing has been apart since last year,I want to ride it again!

[NordieBoy]

Do it.
Ride it.

Now.

[XTC]

So is it gonna be ready for clint's ride or not? Even if you have to put the DT plate on it.

[Motu]

So,the cases are together,piston and barrel on and assembling the primary side.Do I fit the SRX kickstart while I'm putting it together? I guess it makes sense to do it now.I fitted the higher capacity 3AJ oil pump from the '94 too,that'll give more oil on the output side.97x67 doesn't look too bad in the flesh,pretty normal really.

It took 11 days to get the gasket set out of DHL - it was addressed correctly from Coyote....this was a DHL stuff up from the start.

[cheese]

4 weeks and I still don't have my pipe from America............

[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 (http://www.kiwibiker.co.nz/forums/showthread.php?t=68072) 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! :weep: :crybaby:

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