The Liner Wars (and Pistons)

Not so much a war - but I had to make a decision about the liners for the re-build.

NB Warrior kindly donated their old liners and pistons to see if they were better than mine. Now it was time to see which ones where the best.

There is no real alternative but to use good old fashioned measuring. And the measuring device – an internal micrometer of course.

Along came the evening when I had the house to myself. The liners duly found themselves on the kitchen table (hence the house to myself) all in a nice neat row.


Now I know, there’s only 5. The left hand three being mine the right hand two being ex’ Warrior (one never made it http://nbwarrior.blogspot.com/2008/03/even-goldfish-can-count-to-three.html)

The first measurement was the very top and very bottom of a liner. This confirms the original (non worn) diameter. Measurements are taken at 90 deg’ at each point to check to see how oval the bore is.

The reference measurements on my original liners was 4.125" (4.1/8th"). All three were spot-on.
Next was measuring the ‘worn area’. I was pleasantly surprised to find each liner gave the same readings of wear:
Longitudinally: 4.128 (3 thou wear). Transverse: 4.130 (5 thou wear) at the top of the stroke and slowly tapering out down to the original diameter as you went down the stroke. A max of 5 thou wear and 2 thou oval. Not a bad result.


Next up was the two (of three) liners from Warrior. The first difference was the original diameter. 4.135" top and bottom. They were both 10 thou oversize. The remaining measurements confirmed that the overall wear was of a similar pattern to mine but 1 thou less on each measurement.

The original factory spec was 4.1/8th" bore and 6" stroke. It would appear the Warriors liners, although slightly less worn than mine, have had a 10 thou re-bore in a previous part of their life.

Which ones to use – well, mine of course. I’ll have a chat with the machine shop, but I think a 5 thou hone from the original diameter to remove the oval bore and "the jobs a good un".

An examination of the pistons found them all to be of a similar condition. Mine have got the oil rings well and truly jammed in and are yet to be eased out. Both sets of pistons have slightly scuffed skirts, but nothing much to worry about. The ring groves are still tight and true. Overall, either set could be recycled with no problems.


All its going to take now is a trip over to Warrior to re-unite them with their 'bits'. Any excuse to see another National will do!

A useful exercise - and thanks to Jim & Sarah for the offer of their old liners and pistons.