Con rod got too much play perhaps?

[XTFraz]

Awright

Got an Xt350 in the process of rebuilding. It was Very smoky when I got it, absolutely chucking it out of the crankcase breather and a little rattly on the top end, when i've stripped the top end the piston shows signs of heat and the bores scratched so methinks it needs a rebore and piston. BUT theres about 3mm sideways play on the conrod when measured at the top (little end). any one know if thats normal or not?

cheers

[themoudie]

Need to measure play at the bottom, either side of the rod. Sounds as though the thrust washers are worn at the very least. Side play for XT600 is 0.25mm -0.75mm or 0.0098thou" - 0.0295thou" between the side of the rod eye and the crankshaft. If it exceeds this, new rod! So it says in the manual

Hope your rods useable!

Regards, Bill.

[XTFraz]

Thanks for that,
had a look thought the manual tonight and side play if I read it right is between 0.35 & 0.85 mm so you weren't far wrong. Anyhow the crank is still in the engine (which is still in the bike) when I [push the rod over to one side making the gap at the top of the crank the widest and zero gap at the bottom the clearance was about 0.61mm (still with me?) that seems ok to me - not that I know much, whats your thoughts?

Cheers

[themoudie]

Aye XTFraz,

By the reading of your mail, you are not pushing the rod to the side squarely. To make an accurate measurement, the rod needs to be moved to the side squarely and the gap then measured.

Therefore, your side float gap with the rod on the sosh and from measuring the widest part of the gap, it would appear that you are within the tolerances in the manual. This is good, but you are measuring the gap using a different method from that assumed by the manual writer. Not always good, if you see what I mean!

Pedantic, I know, but it can cause grief. Literally.

I hope the rebuild goes well and the engine lasts for many more miles.

Regards, Bill.

[guest27]

If the rod is rocking on the big end does that not suggest knackered big end - or have I misread the post?

R

[themoudie]

Aye Rog,

Could do, but we haven't explored 'up', 'down' play, just been side playing. Have to admit that it could be a possibility.

In which case XTFraz, bring crankshaft up to Top Dead Centre (so that the bottom of the rod is near the crankcase mouth), hold the crank so that it is unable to rotate and see if you can lift or lower the rod anymore by gripping it halfway along its length, between forefinger and thumb and applying light pressure. If you can feel ANY play/slack/or hear ANY click/knock, I would suggest splitting the cases and getting the crank checked out by an experienced engineer. Better to spend the money now, rather than rebuild the top end and have the big end let fly and destroy the whole motor!

If this still doesn't explain things clearly, please say and I or somebody else will try again.

My regards, Bill.

[XTFraz]

Bill

I tried what you suggested and can feel nothing vertically, I,m going to check the side thrust again properly this time to check it and then Imight just lift the motor out and take it to the local bike shop for a second opinion, the only thing is they don,t seem much interested unless its a scooter or R1 Blade etc. but asking doesn't cost anything i suppose. Thanks for the advice so far, still struggling to find somebody to rebore it mind.

Fraz

[themoudie]

Aye Fraz,

May we ask your locale discretely?

We maybe able to advise on potential engineers, as opposed to 'plastic pogo stick floggers', "Service sir?, part exchange this October sir!". Smudge has some good tales

My regards, Bill.

[XTFraz]

Bill

North Cumbria -  been looking around for someone locally to rebore and found nothing, posted a few questions here and there with no response so found a company called Jetbore and also just found someone in Derbyshire called SEP (Service Exchange Parts) so might try them to get a price, but Derbyshires a bit far. Could possibly carrier the engine to someone.

Cheers

Fraz

[themoudie]

Aye Fraz,

My old stamping ground at one time, suspect things have changed but try these:

Jack Horseman Motorcycles Ltd.   
 39 London Road
 Carlisle
 Cumbria
 CA1 2JZ
 
Telephone: 01228-545333

(Used to race in Island and were main Velo agents many moons ago.)

Another racing lineage dealership, know about bikes and may offer help and advice, Crooks Suzuki:

http://www.crooks-suzuki.com/

Your local MAG list of Engineers and goodness knows what else, maybe a diamond amongst 'em:

http://www.cumbriamag.com/salesparerecovery.htm

This last one may seem a bit odd, but some of these 'boys' will have served apprenticships with the like of Rolls Royce, Vickers etc and know what they are about. Have a blether!

Carlisle And District Model Engineering Society
39 Holmacres Drive,
Carlisle,
Cumbria CA1 3AB

All the best and let us know how you get on.

My regards, Bill.