Hello Guest User,

Please feel free to have a look around the forum but be aware that as an unregistered guest you can't see all of it and you can't post.

To access these 'Registered Users Only' areas simply register and login.

1170 conversion

Need help restoring, building, or finding then try here.

Moderators: chrisu, paul doran, Taffus, KeithZ1R

Message
Author
Pipes66
new poster
Posts: 4
Joined: 11th Sep 2017
Location: Rugby

1170 conversion

#1 PostAuthor: Pipes66 » Fri Apr 13, 2018 1:59 pm

Hi guys,
I'm bewildered with the amount of threads on here about the 1170 conversion.
I've got a P&M race bike with original to 1980 69.5mm yoshimura pistons and cams. I believe the bottom end is 1000 and the barrels are 900 bored to 1001cc.
Have I got it correct that I need an 82 j head,ported with 36mm carbs and the j cylinders with standard pistons from something or other?

slappa13
100Club
100Club
Posts: 240
Joined: 20th Jun 2009
Location: Lakenheath suffolk

Re: 1170 conversion

#2 PostAuthor: slappa13 » Fri Apr 13, 2018 4:59 pm

You can use a J head but not the barrels, you can also use J GPZ 1170 pistons in resleeved 1015 barrels with a spacer under the barrels
Attachments
EAE540D4-C567-49A6-A57F-C7EECA6C96B8.jpeg

User avatar
zed1015
Hardcore
Hardcore
Posts: 3798
Joined: 2nd Nov 2005
Location: Somewhere between Scunny and Goole.

Re: 1170 conversion

#3 PostAuthor: zed1015 » Fri Apr 13, 2018 6:28 pm

Do you mean you have a 998 J engine ( no provision for kickstart ) with Yoshi pistons or a bored out 900 block on a 1000 bottom ( with provision for a kickstart) ?
1170 is the overbore for the 1000J or GPZ 1100 when using GPZ1100 barrels and this is not a simple fit to the early engine.
If you have a kickstart engine you can go the 1030cc on the 900 barrels and 1075cc on the 1015 barrels.
You can push the 900 to 1045cc and the 1015 to 1105cc but this leaves the liners a little thin and under hard use the liners distort, burn oil and can crack at the spigot..
Anything bigger than the above sizes needs either the blocks re-sleeving or a big block fitted.
903 or 1015 barrels will resleeve nicely to 1200cc.
You can go to 1260 but these liners are slightly bigger and can break through the alloy block when boring it out to take them.
A J head can be fitted to the earlier engine with the addition of an idler conversion but beware that it has larger 40cc, 70mm hemi, combustion chambers and the compression will drop by approx 2 points (i.e 10 to 1 will become 8 to 1) unless you compensate with suitable pistons.
Pics of your engine would be good to determine what you have.
There are lots of possibilities to mix and match with the two types of engine but some machining is involved if wanting to fit later J/GPZ top end on the early case because of the two types of camchain.


Return to “Bike Help”

Who is online

Users browsing this forum: No registered users and 83 guests