Check-list for a bottom end re-build

**Pevrilito** · #1 26th March 2007

Hi everyone,

Hope you're all merry and bright!

OK...I've got an XT350 --- 1989 and the pesky countershaft has gone and lost all its splines, so it just sits and spins inside the drive cog. With 66,000 miles on her, I'm thinking its time to shift my mechanicing skills up a notch (or five! ;-) and do an over-haul/rebuild of the bottom end. (Top-end is ok - there's a new piston and cylinder in there already).

The question is - What should I replace? The current list is:

Countershaft
Timing chain

and I'll also cast an eye over the

Oil pump
Clutch (was on the list before the countershaft went zzwzz)

...and I feel i should replace the bearings and oil seals for the transmission shafts, the balancer shaft and crankshaft but I don't have the tools that my Clymer manual tells me I need [a crankcase seperating tool and a crankshaft installing tool] How vital are these tools? Is it possible to make them or improvise? [I could take it down to a mechanic for these steps, I guess]

So, is there anything I should look out for? (eg. do XT350s have the same 5th gear issue as other bigger XTs)
What is missing from the list?
Any little pins/grommets/bushes etc that I don't actually remove in the general process that i should renew along the way?

Help and advice greatly appreciated...

Cheers,

Pev

***Touring Ted*** · #2 27th March 2007

May I ask what your experiene with engine rebuilds is ???

The margin for error is huge here with such a big job. One misplaced o-ring or badly seated lockring and your bike is scrap.

Splitting the crankcase is a pain in the arse enough WITH the correct tools so bodging it is not good no.

If your going to do this job, first thing to do is strip down the bike and get the engine out..

Its a small and relatively simple engine but if you have never removed things like a clutch, gear shift mechanism and gearbox before, then your best off finding to someone to supervise.

Things come apart easy.. getting them back together is where experience is required.

**aukeboss** · #3 27th March 2007

I started this type of sports with dropping an outboard in the water, letting it rot for half a year and then, without any exprience, repairing it.
So: no guts no glory.
Assuming the engine of the 350 is similar to the 600, it is not as difficult as it looks.
Before removing the engine from the frame, make sure to loosen the big nuts on crankshaft, balancer shaft (have one), clutch and flywheel.
Crankcase splitter: never heard of such a device, always split my cases with some well aimed blows with the rubber mallet.
Removing crankshaft: could be done also by just inserting two bolts in the pretapped holes in left hand case (at least, that's the 600). To install: warm up the case in warm water, and put the crankshaft in the freezer for one night. It'll flip in easily. To remove / install the bearings, go to machineshop with a press.
While you're in there, replacement of all bearings, O-rings and seals is a good idea. Other items, as needed. Give special attention to conrod / bigend.

Now, most importantly: always keep using your brain; keep using your Clymer, and check, check and recheck. An before forcig something, first think!
And work clean.
And for Yamaha's: if it does not fit, it is installed in the wrong way, do not force it but stop and think!

The above, combined with some luck should see you through fine.

Auke

**Pevrilito** · #4 29th March 2007

Thanks for getting back...advice duly noted.

Yup - I know it's gonna be a step-up in mechanic-ing, but it's gotta get done and I fancy having a stab at doing it - especially with the alternative being multiple quids to a mechanic and learning nothing!!

I'm sure I'll be posting again!...

Cheers
Pev

**Pevrilito** · #5 7th November 2007

Hey Aukeboss - It's been late in posting, but cheers for the support - much appreciated!

-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
LESSONS LEARNED
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-

- thoroughly reading all the chapters in the manual first and making a list of all the things, parts and their numbers needed was a good way of focusing...PDF diagrams are invaluable for when you phone the dealer

- I put a fraction of the money I would have spent on a mechanic into reasonably good tools...you can't do it with allen keys from the thrift/pound shop!

- I'm MIGHTY glad I took digital pictures of every stage of the dismantling...you think you'll remember how things were, but I looked back at some of them a good few times later

- A high degree of cleanliness and organisation is needed...everything was cleaned in petrol...all the cogs/washers/locknuts etc were threaded onto zip-lock ties in the order I took them off...everything was put in little plastic bags and and labelled with a bit of masking tape and indelible pen.

- a strong magnet on a stick is great for holding nuts and bolts...and for getting them out of a jam jar of petrol when cleaning them.

- Even so, I didn't need any "unusual" tools for spliting crankcases etc...
...but the biggest tooling issue was undoing the big nut that holds on the clutch because the whole lot just spins. The manual says use a 'Grabbit' ....(a what?!?).... but I worked out that a carefully placed smallish G-clamp would compress the old clutch plates enough to slacken that pesky central nut.

- a impact screwdriver is scary to use but can work miracles...

- and similarly....a sturdy old brace (an old fashioned type of wood-drill) will apply a LOT of STEADY pressure (by getting your girlfriend to sit on the end of it!!) to undo screws etc

- and similarly.... WD40 is an eixir of the gods!

- you really need to make sure that you've got all your dogs and gaps and gears aligned correctly when it comes to meshing the two gear shafts together!!! Grrrr!!

- once you've put your your reassembled bottom end back on the bike ready to put the piston... you need to make sure that no bloody rain gets inside it!!! Grrrr!

- those stainles steel allen-key hex-bolt kits from ebay are a great replacement for the old and shredded crank-/side-/ and carb case bolts

*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-

All told, it was a long lesson, but the engine (and beyond!) was stripped to individual nut, bolts and bearings....reassembled...and then driven on a 4 week tour round Scotland, Ireland, Wales and England...WooHoo!

**Walkabout** · #6 7th November 2007

Hi,
I have not done a bottom end but a top end was a big learning curve for me as well - your check list is very useful (based on hard experience) and I can identify with all of the items that applied to my top end work!!
For a beginner, you cannot take enough digi pics as the bike is dismantled.

About the experience aspect; when I was finished, I felt that I knew every nut and bolt and moving bit going around in there and that sort of gave me increased empathy with the bike when riding it - dumb I know, but..........

Cheers,

**aukeboss** · #7 7th November 2007

and congratulations! Welcome to the black fingernail society ...

A bit late but for your next time that is hopeflly many miles away ... to loosen the nut on the clutch ... put bike in gear ... fix rear wheel with some kind of sturdy strap around rimlock bolt or spoke nipple ... and away with the socket! ... to assemble, reverse the order.

Auke