Thanks guys. I have ordered the compression version from Halfords as it’s universal and I can lend it out to the local group if needs be.  Cambridge motorsport do the specific sized taper versions at nearly £50 ( as well as the forged pistons !! )  

The taper bore style John is showing works very well, it is this design we use on the big marine engines. You can either buy one (not sure where one would look mind you) or if you happen to know someone with a lathe it would be a relatively easy job to make one. But otherwise, yeah the Halfords version will do the job perfectly fine, just a bit more faff. For a one off job, Halfords style all the way, however if you expect to do this a few times (and lets face it, engine rebuilds are a normal part of competing) then definitely go for John's option.

Hamish, Those wide coils of spring steel that you wind up tight around the piston to squeeze the rings in to insert them in the bores are OK, but I've been most impressed by a 'ring compressor'.    A stumpy cylinder with a conical bore that you position over the bore and push the piston down into it. Of course you need one that precisely matches the bore diameter! JOhn

It will run awfully while you do it, but you can fix the advance to 0° set the crank sensor offset angle by using the a basic timing gun and lining up the crank pulley timing mark with the timing chain cover.  I found this a useful sanity check when getting mine up and running.  Of course this is likely off by a couple of degrees unless you calculated exact top dead centre with a piston stop and calibrated the crank pulley and timing cover marks!   Can I ask you to share the AFR table you're running please?  I think you're running a small crank 1300 engine same as me.  My setup (still SU carbs and standard camshaft) is running fairly rich across the board, but the AFR table I have to compare the logs to seems quite lean, so I'd really like to compare against a better AFR table.

That'll do it! Good spot and nice to hear you're making real progress 

Mine too 

Sadly the next step would be forged pistons. in the region of  £1350.00 a set   I am doing a “budget” repair with a set of pistons, rings and composite head gaskets as well as sundry gaskets. the pistons may need machining to deck them. Which I’ll have to find a local machine shop. Been told I need 15thou clearance to top of liners plus that gasket thickness. need to ask for big end bolt torque need to buy a piston ring compressor fitting tool i see Halfords still do them  any good ?     I guess I need to compromise on revs !!? https://www.halfords.com/tools/hand-tools/all-hand-tools/laser-piston-ring-compressor-696591.html?istCompanyId=b8708c57-7a02-4cf6-b2c0-dc36b54a327e&istFeedId=367c5610-f937-4c81-8609-f84582324cd6&istItemId=xxpmxi&istBid=t&gclsrc=aw.ds&&_$ja=tsid:|cid:17363835999|agid:|tid:|crid:|nw:x|rnd:7701894720434988961|dvc:m|adp:|mt:|loc:1006648&gad_source=1&gbraid=0AAAAADrJx6wTRhyBhoCbJAGhShMaF_LaG&gclid=Cj0KCQjw8cHABhC-ARIsAJnY12wCsJPdTVUno333bYRzFl6kF5BToHfnj7fVB8giKjpVL1KzH8FVGGUaAmsQEALw_wcB    

Thanks Nick - I'll speak with Dave as he's holding some parts that I need to collect, so could be an excuse to go over and collect them.  If I learn anything useful I'll share here....  

Ah, bollocks - it was going so well  Does look rather like a repeat of the previous problem.  Reckon you are finding the limit of the standard pistons!  Is there anything better out that that won't smoke your wallet?

Hi Will, Don't have a very good answer to your question.  You could try ringing Paul Hughes at 2Spec Transmissions and asking what he suggests - he's a Triumph guy who build diffs.  Or Dave at Canleys - he's built many diffs too. There are various engineering supply companies that do sell shims but typically metric and typically in packets of "many", though not necessarily expensive.