Jump to content

series 2 piston bore


Recommended Posts

We have had an old series 2 sat on the farm and Im fixing it as a fun side project. I was told there is an issue with the piston and so im looking to get replacements (been looking round). However, self centering 3 point bore gauges and micrometers are expensive for something im going to use one time.

Im thinking of using a 150mm caliper as a guide. You can also get calipers that also read upto the micron level.  Has anyone ever done this? and what would be the best approach on a budget? 


Best regards, 

Link to comment
Share on other sites

A calliper won't tell you how worn the bores are. I suggest that you look for a bore comparator which you then measure with a calliper or micrometer.

A huge word of warning; you can do a great deal of damage if you have lipped bores and go down the cheap route of new pistons and rings without reboring. The new rings could hit the lip and you might be in for a big repair bill.... 

  • Like 1
Link to comment
Share on other sites

As stated above you can't directly measure bore wear with a digital calipers as it won't reach beyond the unworn part of the bore that the top rings don't reach.

As a crude but useful starting point, find a bit of thick fencing wire or similar, cut a straight bit to about 3mm more than the bore . Round the ends into a smooth roughly spherical shape and then bend it in the middle so that it JUST fits into the bore. You can then measure this with the calipers and if the wire is stiff enough and you had the right feel of it in the bore you will have a useful idea of the size at that point. do the same at several points on each bore and you should have an idea of the situation.

If there is a big step at the top of the bore at the limit of where the top ring reaches, that will break new rings even if the diameter is acceptable so it would need removing anyway. Maximum wear is usually a little below that step and across the axis of the engine. Any deep grooves from broken rings or debris are bad but depending on severity and intended use you might try to hone them. Ideally a rebore, new pistons, rings and all bearings and gaskets is the way to go.

A good quality digital caliper (not a £5 one!) is a basic tool that you need for any work of this kind.

Have fun and work slowly and carefully.


Edited by David Herbert
  • Like 1
Link to comment
Share on other sites

It’s a tricky call…

a big gap between making it “go” and making it right. Maybe best to go one way or the other. Stepped top rings used to used to fix things up for a while. F.W. Thornton for pistons & rings?

Best steam practice was to increase the bore above the area swept by the rings so wear did not cause a step. The S1 was the same.

you could possibly get an idea with a good calliper, bare piston and feeler gauges.

how invested do you want to be? 

Agree with previous posts.

happy fixing up


Link to comment
Share on other sites

S2A  were the days of 'selective assembly' and graded pistons (check crowns for size & grade).  If worn you could use oil control rings ,  3 slip hones are overtaken by  "Flex-Hone"  many engine plants inc. Perkins have used them for 40 years +   Snap on (among others) sell them.  With 2.1/4 pet. I use a Makita variable drill 0 ro 500 max. rpm.    Any ridge , you can use a buster called a RIDGE REAMER ,   I just use a die-grinder to remove stock & finish with round India slips.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...