Don't want these Ads? Why not sign up as a Trials Central Supporter.

haybob

Main bearings 159

4 posts in this topic

How to check the crank big end for ware ? , It feels tight and no play , also the side movement of the Con rod is just over 1 mm , I will replace the small end . is there any other way to make sure all is ok before I rebore cylinder and rebuild the motor , thanks 

Share this post


Link to post
Share on other sites

Don't want these Ads? Why not sign up as a Trials Central Supporter.

Posted (edited)

When replacing the main bearings do I fit them so they are flush with in side of the crank casing , has there is no lip to stop the bearing from going in to far and letting the crank touch the engine casing ,, thanks for any advice 

Edited by haybob

Share this post


Link to post
Share on other sites

Posted (edited)

1 hour ago, haybob said:

How to check the crank big end for ware ? , It feels tight and no play , also the side movement of the Con rod is just over 1 mm , I will replace the small end . is there any other way to make sure all is ok before I rebore cylinder and rebuild the motor , thanks 

Wash the big end out and dry it with air then give it a squirt of WD40 or similar - if it's full of gluggy oil you won't feel the wear so clearly. Sit the crank on the bench and position the rod so that it's at or near the TDC position. Hold the rod between the thumb and forefingers of both hands, near the bottom of the rod so your hands are resting on the crank. Push the rod up and down and feel for any play in the bearing. Take your time doing this; if the rod isn't held perfectly perpendicular to the crankpin (looking from the front or rear) you won't feel any wear that's present. If you don't feel any vertical movement and the rod turns smoothly without any perceptible roughness and there's no sign of heat (like blueing) on the big end it's good to go. Don't forget to oil it before buttoning up the top end. Check the surface of the little end bore for wear and pitting while you're at it.

1 hour ago, haybob said:

When replacing the main bearings do I fit them so they are flush with in side of the crank casing , has there is no lip to stop the bearing from going in to far and letting the crank touch the engine casing ,, thanks for any advice 

The method I use is to fit the bearings to the crank first; they need to go right up against the shoulder. Warming the cases lets the bearings go in easily (there's a whole thread on this procedure here - everyone has their own preferred method) and a little oil on the case bores helps too. The seal retainers locate the bearings (and the crank) axially in the cases so that the crank is centred and nothing rubs. Replace the crank seals and o rings while you're at it.

Edited by oldjohn
2 people like this

Share this post


Link to post
Share on other sites
3 hours ago, oldjohn said:

Wash the big end out and dry it with air then give it a squirt of WD40 or similar - if it's full of gluggy oil you won't feel the wear so clearly. Sit the crank on the bench and position the rod so that it's at or near the TDC position. Hold the rod between the thumb and forefingers of both hands, near the bottom of the rod so your hands are resting on the crank. Push the rod up and down and feel for any play in the bearing. Take your time doing this; if the rod isn't held perfectly perpendicular to the crankpin (looking from the front or rear) you won't feel any wear that's present. If you don't feel any vertical movement and the rod turns smoothly without any perceptible roughness and there's no sign of heat (like blueing) on the big end it's good to go. Don't forget to oil it before buttoning up the top end. Check the surface of the little end bore for wear and pitting while you're at it.

The method I use is to fit the bearings to the crank first; they need to go right up against the shoulder. Warming the cases lets the bearings go in easily (there's a whole thread on this procedure here - everyone has their own preferred method) and a little oil on the case bores helps too. The seal retainers locate the bearings (and the crank) axially in the cases so that the crank is centred and nothing rubs. Replace the crank seals and o rings while you're at it.

Thanks for the advice 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now