Bantam piston.

[rhyatt]

Do you have an engine reconditioner near you that you can take the barrel, rings and piston to.
They'll be able to measure what you have and what you need.
Yes , rings can be filed to achieve the correct end gap , but 2 stroke rings are pegged making a bit more difficult

[scousebantam]

Measured the bore yesterday with a vernier gauge and the bore is 2.432" piston is 2.427". Which measures up to the 0.005" gap that you advised me to take earlier of piston to bore.
I looked at the instruction manual I have and it gives measurements in mm, so I will do it again today to see if it measures up to standard bore of
61.5mm. 

[scousebantam]

Just measured the bore and it reads,  61.76mm the standard bore is 61.5mm. The difference .26mm equates to 0.010".
The piston I have that fits the bore reads,  0.020 with the letter R stamped on the crown, the piston has a domed crown,
unlike the original piston which was flat across the crown.
Totally baffled.

[rhyatt]

Ok- I think I see the issue

you have a +10 cylinder barrel and a + 20 piston(is this the piston that you mention was scored etc??)

if you have ordered +20 piston rings and then are now trying to squeeze them in to a +10 bore, then this is the reason that you have .005 end gaps on the rings.

I think I see 2 options - maybe 3

1) exchange the rings for some +10 and try to find a +10 piston to fit them onto( but you don't actually know the "truth" or roundness of your cylinder barrel - so this route could be wasted time and money.

2) either speak to Cox and Turner to see if you can post your +10 cylinder barrel to them for them to measure and  if necessary rebore and at the same time supply a correct brand new piston to fit the newly rebored barrel - this basically starts everything anew.

3) if you have an engine reconditioner near to you and they are conpetent on 2 strokes , approach them for them to measure and if necessary rebore close to you to deliver/collect

My own D7 has a hotchpotch of barrels and pistons and I eventually went down the route of (2) - but I live reasonably close to them

https://www.yell.com/ucs/UcsSearchAction.do?scrambleSeed=211022062&keywords=engine+reconditioners&location=yeovil

you'll have to put your own town or post code into the search box(cox and turner are down the list)

my rebore/piston was about £150

[scousebantam]

Brilliant, I didn't see that, I was told that they were matching Barrel/Piston so didn't think outside the box, well done for that rhyatt.
I do have a very good automotive engineers less than a mile away, or did have years ago (they done all my re-bores many years ago),
don't know if they are still there, I will know Monday.
As I said before it depends on the reliability of the source you buy from. 

[scousebantam]

ryhatt, that's what I wanted to ask you, in one of your previous posts you said the gap between piston and bore should be 0.004" or 0.005",
which mine is already, if I get the barrel re-bored to +20 (from +10) that 4 or 5 thou gap will be a lot more?

[rhyatt]

The piston to bore clearance is a constant gap to allow for the aluminium piston to expand in a cast iron cylinder.
Irrespective of standard or plus 10 or plus 20 plus 40.
Your local chap may appreciate looking at the bsa specs to enable him to bore correctly.⁹
Go and see him, take your barrel and piston and rings, see what he can suggest as a way forwards.

[scousebantam]

I think my best option at this time is to get another barrel if I can, if anyone has a standard barrel that they want to get rid of I can assure them it will be going to a good home.
By the time I get my cylinder re-bored and the head cut to take the high compression piston it will cost me a fortune, I need to cut my costs, at least I have a plus 0.020" high compression piston with new rings (which cost me £37.00) if anyone is interested?
So, I am in the market for a standard D7 barrel, if there is one spare out there, I know I will have to buy more piston rings, but that is my cheapest option.
Thanks all for all your help, it has been appreciated. AND I have learnt a lot.   

[scousebantam]

rhyatt, we were talking about automotive engineers and I said that there used to be, well I went to see them today they are still there and they now take up both sides of the road and they said they couldn't do any automotive stuff because they don't have the tooling to do such small work, they now do heavy industrial work. How times change.
Anyway, I went back to basics, I put a pair of inside callipers in the bore and fixed them, when I went across the tips of the callipers with the verniers they measured 61.76mm.
I am therefore fairly confident to say that they are +10 over standard, and I compared the head with FAQ's on the other site and I am happy that I have D7 barrel and head.
Thanks for your advice.   

[rhyatt]

Ok
So if you're confident that a plus 10 piston will get it running, then go for finding 1 somewhere, you have Kidderminster 01562 66679
Or chasbike but I don't have his number sorry.

If you find that a plus 10 piston is completely unavailable , then you'll be looking at a plus 20 rebore and a new piston .
Of course, if that route happens , you already have plus 20 rings, so just need a plus 20 naked piston

[scousebantam]

Conclusion;
ryhatt I took your advice, took my barrel to a racing motorbike engineers, less than 3 miles from home, he measured the top, middle and bottom of the cylinder and informed me that there was different readings at all 3 points and advised me to bore out to +40.
I have ordered a piston and rings from Cox & Turner, when it arrives I have to take it to the engineers so that he can hone the cylinder to match the pistons. 
Think I am now on the right road, thanks to everyone who helped along the way, much appreciated.

[rhyatt]

Glad progressing

[scousebantam]

Just one thing before I pack this thread in please, my engineer has got my barrel and piston and I am picking them up tomorrow but one final question as a matter of interest.
Is it normal that when a cylinder is re-bored the new piston is slightly domed, I ask because Cox & Turner from whom I purchased the new piston and rings said it was a standard flat top piston at 0.040", but it is not, it has a very slight domed crown, or at least not as flat as my original piston. If you know what I mean.   

[rhyatt]

Difficult to suggest, but I think Rex Gaunt has alloy 0.5 thick and a 1.5 thick head gaskets if clearance is a problem

[scousebantam]

That is handy to know, spoke to my new friend (I think that is one sided though) the motor engineer, and he said try the old solder trick
to see how close the piston is to the head.
Just picked up my cylinder, honed for the piston and no sharp edges, he also loosened my flywheel nut, he has the right tools, all for
50 quid. I thought it was a good price but, no real experience to judge.
He can put a squish band in the head if I need it.
Onwards and upwards.