ET: Engine (Twin) Piston Choice

[Black Flash]

I would always go for 8:1 pistons to boost economy and get some extra umph.
Iirc during the period the bikes were built they had to run on low octane pool petrol. If they had better fuel I am sure they would have been built with a higher cr in the first place.
If you are unhappy you can always fit decompression plates during the winter. It also gives you the chance to escape for a few hours for a couple of days,iyswim.

 

[vibrac]

Here is an argumentative statement.
In today's speed restricted UK it is a valid question to ask what's wrong with 7:1 pistons or even lower I think it would certainly lead to far lower sales of electric starts and twins kept longer

 

[deejay499]

I rode the Ulver’s outfit with 6 something compression and it was delightful. So easy to start, easy running in town but still went OK.

 

[Bill Thomas]

Your are both Right, But I can't bring myself to agree !, So It's 9 to 1 and Mk2 cams for me. Cheers Bill.

 

[van drenth]

Your are both Right, But I can't bring myself to agree !, So It's 9 to 1 and Mk2 cams for me. Cheers Bill.

I got them in mine Blackshadow but very hard to start specialy when you are short legged like me.
Regards, Jan van Drenth

 

[Bill Thomas]

Funny the Bike with 36mm Dellortos, Starts OK, Because it has proper Chokes, But I don't have the Mk2 Amal
chokes sorted yet, For fast idle. Cheers Bill.

 

[stu spalding]

I have cracked three 7.2/1 comp pistons and I am convinced that obtaining the lower comp ratio by machining material from the crown on an 8/1 weakens it. I now run 8/1 pistons with compression plates to get the ratio down to 7.2/1. Cheers, Stu.

 

[clevtrev]

I rode the Ulver’s outfit with 6 something compression and it was delightful. So easy to start, easy running in town but still went OK.

Alfa sud pistons.

 

[Monkeypants]

I have an 8 to one Rapide that works well. It's an extremely easy starter.
In a pinch it has run it on regular fuel without any problems. I normally run Chevron Supreme ethanol free , however when out touring sometimes regular fuel is the only type available.
55,000 miles , low e pistons , originally set up with 3.5 thou clearance .
Honda Chrome rings and no ridge, bore wear negligible.
Glen

 

[Bill Thomas]

Alfa sud pistons.

Is there an easy way of fitting them yet Trev', Cheers Bill.