750 head on 850 barrel

What is the problem when fitting a 750 head (after changing the outer head bolt spacing) on a 850 barrel , without re -hemispher the head ......? will increase the CR for sure , will it work ........? more turbulences ........? just thinking

By the time you open up the squish bore to 78.5mm the compression will be about the same.

The smaller ports will be a plus on a street engine. Jim

I was just thinking of not opening the squish bore ........? and fitting 850 flat top pistons which do not protrude as the 750 doe, when we had done it for the 750 Maney jugs it was only because it had a 850 bolt pattern , so it was easy just plug two outer head bolts holes and redone the correct spacing ......

On that note was there ever a 73 mm bore sleeved ? 850 type cylinder and head to suit.
Folk seem to like bigger capacity engines but that would make for a tough 750 in stock form. (compared to the early engine case and cylinder)

Time Warp said:

On that note was there ever a 73 mm bore sleeved ? 850 type cylinder and head to suit.
Folk seem to like bigger capacity engines but that would make for a tough 750 in stock form. (compared to the early engine case and cylinder)

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Steve Maney used to supply his alloy cylinders with 73 mm bore sleeves and 850 head bolt patterns on request. I used to get similar alloy cylinders from Drew Robertson many years ago, but I don't know if anyone is still making them. I believe AN can supply 73 mm bore iron cylinders with through bolts, like the 850, but don't know if they can do them with 850 head bolt pattern. Might be worth asking them.

Ken

Time Warp said:

On that note was there ever a 73 mm bore sleeved ? 850 type cylinder and head to suit.
Folk seem to like bigger capacity engines but that would make for a tough 750 in stock form. (compared to the early engine case and cylinder)

Click to expand...

I have dropped sleeves in an 850 engine to make them race legal. It works great. Jim

Here's a 750 head on 850 cylinders (my old monoshock racer). If you carefully elongate the four outer bolt holes near the head and check that there is some area left to clamp the head gasket - you're fine (it worked for me). I think this is also what Steve Maney used to do. Or you can plug the holes like Ken Canaga did and re-machine.



The head originally had 28mm ports and that gave me plenty of design room to give it raised ports which ended up as wide and high as I could get them without welding without going too far beyond Axtell's port specs.

Before it went on the 850, the same head was raced in my Featherbed 750 (stock valves with raised 32mm ports) and managed a 2nd place at Laguna Seca in 1984 (below).

Hi Jim (s), both of you ! just asking about the non -matching 750 head hemisphere/850 jug bore , just to know if it is a non sens ??

marinatlas said:

Hi Jim (s), both of you ! just asking about the non -matching 750 head hemisphere/850 jug bore , just to know if it is a non sens ??

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The hemisphere is the same between a 750 and 850.

Thanks !