Custom pistons

[Woodman]

I am just at the point of rebuilding my old Benelli, and I need a 78mm piston made. original bore is 74mm, but I bored it out years ago when I was an engine reconditioner, and am way out of touch on who does what where now.

What I need to know is there anyone in NZ that does this now?, Denco used to but couldn't find any info online tonight. Arias, JE and Wiseco have custom build programmes, but I would rather deal with someone a bit closer etc.

My other question is, does anyone have a resource of piston sizes/specs etc that is easily accessible.

Cheers

[Dan Mapp]

I would of said Denco as well.

[Dan Mapp]

Denco Engineering 1987 Ltd
419 Tuam Street, Linwood, Christchurch City, Canterbury Telephone
(03) 3812111

[Kickaha]

There is a guy in Beaumont street, Christchurch who used to import blanks and machine them, Ross ( I think)will no longer supply blanks to him but he does custom orders through them, it was about $400-$450 for a one off, for a four cylinder it was slightly cheaper per piston

My other question is, does anyone have a resource of piston sizes/specs etc that is easily accessible.

I've yet to find one and lately I've had a good look, but you can search the Wiseco site and some of the others

A quick search gives these plus Honda CRF250
JE do a few 78mm pistons for big bore GSX1100 and GPZ1100 but then you need the right pin size, compression height etc etc

[Woodman]

Cheers, will look harder next time. will give Denco a call next week.

[Motu]

Back years ago when you were probably still in the game,there was a guy in Auckland casting blanks in various sizes.I got him to make a set for a Mercedes 250 - machined up and fitted with MkII Zephyr rings they were still half the price of genuine.Just a small industrial unit with a furnace the size of a washing machine - I bet there are guys still doing such things around the country.

[Woodman]

I had a look at a few of the sites, but most of the ones of the right bore size have domes etc and the benelli is flat. Also most have only 16mm pins and I need a 19mm. I could rebush, but nah the bottom end is together and bushing a rod in place is a pita re alignment etc. Will get one made, but will see if I can stretch her out to 80mm bore. \
80 x 57 bore x stroke is not very square aye.

[Kickaha]

Will get one made, but will see if I can stretch her out to 80mm bore. \
80 x 57 bore x stroke is not very square aye.

Ducati 600SS is 80mm bore might be worth a look, most engines are now going quite oversquare so I wouldn't let that bother you

[Wheeliemonsta]

Kawasaki ZX1200-C (ZZR 1200) use's a 78 mm bore standard... There a very good quality piston it would depend on the pin size (17mm if i'm not mistaken) & crown height from pin centreline etc etc... Worth a look if suitable

Cheers

[Motu]

I had a look at a few of the sites, but most of the ones of the right bore size have domes etc and the benelli is flat. Also most have only 16mm pins and I need a 19mm.

It's a matter of looking around,which of course you are doing right now.The guy who made me the Mercedes pistons showed me some of his work,and one was a big bore 2 stroke piston,over the 80mm mark at least.Flat top and thin and light with cut aways as per 2 stroke - it can't be a lost art surely?

[Woodman]

Just been out to the shed and measured things up . I bored it to 77mm and the pin size is 18mm. Funny how time messes with your mind eh? Actually these sizes are pretty close to xr250 wiseco 280cc big bore size as long as the c.h is similar. Mind you the price difference between a wiseco one and a custom one is not much.

The other thing I left unfinished before leaving the trade was I did some porting and bigger valve work on the head and didn't make up any valves to suit so there is a bit of work there too. I really miss having access to a machine shop.

[Grumph]

Can't help with a 77mm piston but the 650 twin uses the same rods as the single - which I assume you've got.
The 650 pistons are 84mm and Road & race in NSW have them in stock.
All the overseas custom piston shops - and their Kiwi agents - now have a minimum order of 4 pistons
Try Proturn Engineering in ChCh - Arias agent - he has a number of part finished blanks on the shelf.

The main problem you'll find with the single is the very short valves and springs.
To get some more lift in there it is possible to deepen the spring pockets - providing you haven't already gone mad in the inlet ports....

[Woodman]

Can't help with a 77mm piston but the 650 twin uses the same rods as the single - which I assume you've got.
The 650 pistons are 84mm and Road & race in NSW have them in stock.
All the overseas custom piston shops - and their Kiwi agents - now have a minimum order of 4 pistons
Try Proturn Engineering in ChCh - Arias agent - he has a number of part finished blanks on the shelf.

The main problem you'll find with the single is the very short valves and springs.
To get some more lift in there it is possible to deepen the spring pockets - providing you haven't already gone mad in the inlet ports....

cheers for the info, but 77mm is actually about the max it can go without making the sleeve too thin where it protrudes out of the barrell.

My Benelli is the 250ss with the horizontal engine. Same basic bike as a Motobi,( it even has a Motobi dipstick), so not sure of interchageability with the 650, but the valves and springs etc are not unusually short and look pretty normal really. If I really wanted to spend the dosh i could get all new parts from the Zanzani people who are still making race versions of these bikes.

[LBD]

I beleive Burt M's recipe was one chev, two Ford....and I think there was some plymouth in there as well....After casting, quench in tea quality rain water.

[Grumph]

The two I've built had valve spring installed heights of 29 and 31mm respectively - I think the 31 was a late SS.
Given the standard cam lift of about .25in and the fact that the standard springs coil bind at about .27in, anyone looking
at tweaking one of these has to look at better springs. I finished up deepening the spring pockets and making deeper retainers too
in order to arrive at a fitted height of around 34mm - which let me use higher lift cams.
The 650 inlet rocker will I think drop in and has a much better ratio.
The standard rockers are pretty much 1:1 - except if you mix them up when the ratio goes negative.....