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Is it worth buying the rex caunt 64mm Piston kit for 45Quid?
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Bantam Sam
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January 24, 2013 - 5:24 pm
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Hi

Wanting to know if the big bore piston kit is any good i was going to use this for trials is there any other mods i have to do after i have fitted this and does it benefit the power in any way?

Cheers Sam

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chunky chips
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January 24, 2013 - 6:37 pm
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Your best bet is to use a D14 cylinder with the Rex piston kit because of the improved porting(will give you a instant increase in horse power) and the high silicone content in the piston will help prevent seizure. Make sure the cylinder head you use will clear the dome of the piston. All Bantam cylinder heads from D10 onwards had a squish cast into them for that very reason. The heads with the plug hole on the angle are the easiest to find and convert if you feel you want a de-compressor.

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Bantam Sam
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January 24, 2013 - 8:47 pm
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Hi Chunky

Think the one i have on the D7 is angled but the guy said there was no specific place to put it so he wasnt willing to take the risk and i may try and get a D10-14 barrel or swap it for my D7 barrel + head  and i am going to enquire how much it is to get the barrel bored out to 64mm

Cheers Sam

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Bantam Sam
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January 24, 2013 - 8:49 pm
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Hi Chunky

Would this do? [Permission to view this media is denied]
hash=item51a5ab3bcf

Cheers Sam

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HowD1
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January 24, 2013 - 9:10 pm
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Hi Sam - I have a similar one fitted to my B175 using a Suzuki piston. Punchy, easy starter - but kick back is a surprise - and seizing woes are drastically reduced. The little end had to be modded, and the skirt needs machining too. But overall well worth the cost and effort.

Rick

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lazybandittattoo
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January 24, 2013 - 9:23 pm
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My D14 has one of Rex Caunt's 64mm pistons in it. If you fit one you will need to machine the cylinder head accordingly. I know a fella who can do this for you. 

 

I think it was worth it. 

 

We can take the head off mine next time you visit the workshop and I'll show you. 

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Bantam Sam
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January 24, 2013 - 9:51 pm
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Thanks for that tony

Are you on about that guy in Huddersfield if so can you give me his number im going to try and price it up do you have a late d10 or D14 barrel?

Cheers Sam

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Bantam Sam
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January 25, 2013 - 4:26 pm
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Hi Rick
My grandad wants to know if the big end will cope with the bigger piston?
Cheers Sam

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lazybandittattoo
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January 25, 2013 - 10:35 pm
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The big end copes ok. It isn't that much bigger. 

 

Will PM you. 

 

I use a D14 Barrel and head. Not got round to swapping for larger bore exhaust yet though. 

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HowD1
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January 25, 2013 - 10:40 pm
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Bantam Sam said
Hi Rick
My grandad wants to know if the big end will cope with the bigger piston?
Cheers Sam

 

Seems to be fine.

Rick

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cyclobutch
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January 29, 2013 - 4:07 pm
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I bought a big bore piston from Rex Caunt just recently. They offer a two ring or single ring for racing. I went for a two ring and from what I can see it’s from a TS185, already modded for the required gudgeon pin size. I’m still accumulating bearings and seals as I figured I’d do the bottom end whilst I’m fooling around so can’t comment further on its suitability at the moment. I don’t imagine it will overly stress the bottom end, though I note they detuned between the D14 to the B175, reducing compression to extend B/End life. I shall be however be interested to compare the old and new pistons for weight when I pull it down as I imagine that will have some bearing on vibration levels at least.

 

Not sure what compression this new piston is supposed to produce, and though I note mention in this thread of head modifications I heard none of that from the supplier. I’m fitting mine onto a D14 motor running in a B175 chassis, though I have a centre plug head on this one and I’m unsure whether these are reduced compression compared to the rear plug head?

Bikes various, including D10/D14 hybrid - now hard tailed to become a Board Track Bantam - 'The Pie Crust Racer'.

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Bantam Sam
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January 29, 2013 - 8:52 pm
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Hi Cyclobutch

I have heard that the centre plug head is meant to be better with power or something like that because i am going to get a decompressor fitted and they mount the spark plug through the top and use the old spark plug hole for the decompressor

Sam

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lazybandittattoo
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January 30, 2013 - 3:12 pm
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cyclobutch said

Not sure what compression this new piston is supposed to produce, and though I note mention in this thread of head modifications I heard none of that from the supplier. I’m fitting mine onto a D14 motor running in a B175 chassis, though I have a centre plug head on this one and I’m unsure whether these are reduced compression compared to the rear plug head?

 


Interesting. Rex provided very thorough information when I purchased mine. The Head needs to be milled away somehow so as the edge of the piston crown doesn't impact on the edges of the combustion chamber. If Compression is kept down to less than 10:1 then there should be no dramas. 

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richardhyatt
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December 2, 2018 - 7:39 pm
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Sorry to chip in with this.

I have a standard d14 engine with its angled plug head , all standard.

I was going to fit a standard rec caunt 61.5 piston into my engine , my bore is standard 61.5.

Do I have to machine anything please or just drop it in and bolt it back together please.

Thanks for help.

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Peterg
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December 2, 2018 - 10:46 pm
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It should be a copy of the original two ring piston with a mild dome, so no mods needed.

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wildun
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December 2, 2018 - 11:06 pm
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agreed. I use Rex Caunt pistons in my 175 engine with no problems. There are no modifications required to piston, barrel or cylinder head. These mods that you have been reading about on this post are only necessary once you fit pistons beyond the sizes of normal BSA rebore/oversize piston specification. Rex's pistons are of excellent quality. There can't be too many Bantams still running standard bore, most will have suffered some incident over the last 48 years+ to require a rebore. On the box from Rex are the skirt clearances, check this before fitting and you will be ok.

1951 Bantam D1 125, 1970 Bantam B175, 1995 Yamaha Diversion 900 and 2016 Honda Integra 750 scooter. Horses for courses, all very different to each other, but a bike for every occasion.

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richardhyatt
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December 3, 2018 - 7:48 pm
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Many thanks to you both

I'll get busy.

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AdrianS
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December 4, 2018 - 9:19 am
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I fitted a 64mm piston to my bike as it had been bored out already to the max size and I had some piston slap. I wouldn't be happy boring out a barrel that was on a standard size or first oversize as the barrels are becoming more difficult to get hold of. Get a worn out barrel and then bore it out.

My bike runs fine with the oversize piston ( D14) - just make sure you use the 1mm head gasket or 2 0.5mm head gaskets.

With regard to modifying the head to avoid piston interference, I have also seen some modified pistons where a small rim has been machined into the edge of the piston face to prevent interference. This saves damaging the head and is also easier to machine. Sorry cant give exact measurements.

I used Dave Hodgkinson in Derby for the rebore - very precise and does it while you wait at a very good price! Decent bloke.

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nickjaxe
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December 4, 2018 - 8:04 pm
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You can get a liner made for the worn out cylinder to take it back to std.

Firm in Wolverhampton make them.

Seems a good way out.

[Permission to view this media is denied]

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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Mannanan
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December 4, 2018 - 11:45 pm
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Nick raises a good point there. PJM are reputable engineers and get excellent feedback from all the Yamaha RD LC blokes. I have used them myself (not for Bantam work) and was very happy with them. It’s a good option if you have reached maximum oversize.

Ed.

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