G80CS/1960: Pistons

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G80CS/1960: Pistons

Postby mdt-son » Mon Aug 03, 2020 11:14 am

Hi gents,

I am looking for a new piston to fit a 1964 G80CS. Desired compression ratio is 10:1.

In this thread

viewtopic.php?f=23&t=21135&p=177021&hilit=pistons+piston+Top+end+woes#p176996

Don Madden mentions PML as the only source for new pistons. However, their pistons reduce CR to 8.3:1 according to their web site which is a bit low to my liking.

I am prepared to venture new territory. In various forums there has been mentioning of converting HD pistons. What is the status on this topic, and which HD pistons / models would be suitable for adoption?
I have also been looking at pistons for the Velocette Venom and Thruxtion models. These engines had a bore of 86 mm and the compression distance "CD" may be about right. Has anyone examined them for suitability?

If there are others looking for these CS pistons, I would be happy to front a group purchase of say forged pistons.

-Knut

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Re: G80CS/1960: Pistons

Postby jack clegg » Tue Aug 04, 2020 10:46 am

PML are not going to produce any more pistons for G80CS. They are also unable to provide replacement parts, i.e. rings, circlips, gudgeon pins, as I found to my dismay. They still have stock & are a good piston, but no spares, so no good.
John Marshall

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Re: G80CS/1960: Pistons

Postby mdt-son » Tue Aug 04, 2020 3:37 pm

Thanks for the update John. This would make it even more important to find a supplier. I can't understand none of the big companies are offering pistons, going by the interest in the G80Cs especially in the US. Have all bikes become museum pieces by now??
Anyway, I am going to be active on this subject.

-Knut

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Re: G80CS/1960: Pistons

Postby g80csp11 » Tue Aug 04, 2020 5:39 pm

Getting pistons manufactured in limited numbers is expensive , and you will find that everyone is only prepared to pay 1960's prices
I had 4 pistons made of my 1927 AJS H4 350SV, and have so far only sold 50%
But I could not find any when I needed them . I used Venolia to manufacture the pistons and Hastings rings but the cost was Circ £175 each

AJS H4 piston advert.jpg


The best pistons are manufactured to original drawings and low expansion aluminium , Hepolite are now made in Italy (JCC), but I have to say are a very good copy of the originals
when they started the rings were rubbish and they had to use Hastings rings from the USA to work
Now teh quality of rings and pistons are excellent and i've used them on my P11 and G15CSR without problems
Wassell own the trade name , and will not manufacture small batches ie less than 1000 and our club only order in much smaller quantities
All I can think is that Nortons and triumphs must have a bigger following or need replacements more often !
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Re: G80CS/1960: Pistons

Postby mdt-son » Wed Aug 05, 2020 9:36 am

Thank you so much for the referral. That's not too bad. A new forged Wiseco piston for BSA DBD34 from Phil Pearson Engineering is £195 each + VAT.
I am prepared for the long haul.

Yes I know, as owners get older expenses are restricted, and these gents may think "why spend on a bike which isn't ridden anyway"?
However, selling bike on? No way! :-)

-Knut

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Re: G80CS/1960: Pistons

Postby g80csp11 » Wed Aug 05, 2020 11:30 am

The only thing I should say I did supply a drawing and a pattern for them to copy

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Re: G80CS/1960: Pistons

Postby DickV » Sat Aug 22, 2020 11:27 pm

I have boxes of parts to build G80 040 thou piston with no rings. So harley has shovel head motor only 015 bigger piston but perfect ring land width for both upper rings. I will have to machine the oil ring land wider on the piston to make it fit. There are used 010 pistons on E bay. good luck, Dick

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Re: G80CS/1960: Pistons

Postby mdt-son » Mon Aug 24, 2020 2:18 pm

Hi Dick,

I take it you meant G80CS. Having looked at images of HD Shovelhead pistons the achievable CR seems a bit low. The application of HD pistons will also have to enlarge valve pockets and create the squish band for 1960- on engines. Is there enough "meat" in the piston head for machining larger valve pockets?

Also, does the compression height ("C") match? From another thread I know the small end bore doesn't match - but that's a minor problem.

If you made this conversion yourself, what was the resulting CR and for which engine year was the adoption tailored?

Thanks,

Knut

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Re: G80CS/1960: Pistons

Postby DickV » Tue Aug 25, 2020 6:06 am

Hi Knut, I am not familiar with all the Model numbers of the G80's . Mine has serial number G80/135275. The thing I was trying to say was, the rings from the Shovelhead will quite easily fit my piston which is stock 8.7-1 . The only modification I have to do is widen the old ring land, then I can use all 3 Shovelhead rings. The Shovelhead piston has smaller rispin diameter. Also the pin height is closer to the ring land which will make it much lower compression. Also it looks heavier but I didn't weigh it yet. I am hoping to restore this parts bike which I purchased. I am new to this kind of bike. I have a couple of Norton Commandos. Dick

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