748 head pic

marvin

Chris, At long last I'm getting around to posting a pic of my 748 head.
If you look you can see a circle drawn from the 95mm head gasket. The stock "circle" for a 748 bore is much smaller so material has to be removed around the valves out to the edge of the new "circle" or the heads won't breathe very well. I also re-contoured the combustion chamber a bit. I don't have a flow bench or know all that much about it so I looked at pics of other heads from known engine builders. With 95mm bore, stock 851 stroke and the flat top Pistal pistons I calculated 12.3-1 cr. (squish set to 1mm) I used 916 cylinders bored by Millennium. the 851 cylinders can not be bored that far. If you look at them the "sleeve" part that fits down into the crankcase bore has a step machined on it, would be too thin. It is my understanding that some 748 cylinders can be bored to 95mm but only the cylinders that don't have a step machined in them. The strada cams (intakes advanced) work very well with the high compression, pulls nicely from about 3K to 9.5K. I got by with a chip that a friend gave me, just pulled the welch plug out of my fuel pressure regulater and bumped the pressure up to give it more fuel. This combo makes for a really nice "revvy" engine. P.S., do a good valve job too!!

Imola

Hi Marvin
Are the pics of your 748 head work ? (found them doing a google search)
I'm about to remove the shrouding on my 748 heads which will fit on a ST2/916 bottom and 916 pistons and barrels.
Just after some tips on the job at hand.

Steve

marvin

Yes, The pic on the left is my head.

Mr.R

Hi Steve,

Have a look at this link they're 916 heads but very similar to Marvin's job, these heads have been skimmed by 1mm.
I'm using this pic' as a guide to modify the combustion chambers on my 888 Corse heads fitted with 37/31 valves. Unshrouding the valves out to the 96mm bore.

http://cjsracing.co.uk/916%20stage%201.JPG

http://cjsracing.co.uk/916%20stg1,skim%20006.JPG

Steve R

Imola

Hi Steve,

I scored a bargain on a 748 crank rods pistons cylinders and complete heads.
all the rest is up for sale and apart from 748 heads.
From what i have read on here doing a search 748 valves are 1mm longer and the combustion chamber
smaller (similar to skimming 916 heads by 1mm ?)

Steve

Mr.R

Imola wroteHi Steve, I scored a bargain on a 748 crank rods pistons cylinders and complete heads. all the rest is up for sale and apart from 748 heads. From what i have read on here doing a search 748 valves are 1mm longer and the combustion chamber smaller (similar to skimming 916 heads by 1mm ?) Steve

Hi Steve,
Yes once you've unshrouded the valves in a 748 head, you're left with something very similar to a skimmed 888/916 head.
748 rods are the same as 916 items.

Steve R

Imola

Mr.R wroteHi Steve, Yes once you've unshrouded the valves in a 748 head, you're left with something very similar to a skimmed 888/916 head. 748 rods are the same as 916 items. Steve R

Hi Steve

Thanks mate
Time to get the dremmel out 😄

Steve K

Mr.R

Imola wroteHi Steve Thanks mate Time to get the dremmel out 😄 Steve K

Personally I'd go with 888/916 heads* and skim them after the work on the chambers, (I can get a pair of heads accurately skimmed for £30) but you crack on chap.

*Oversize valves are still available for these heads**, but they're getting harder to come by "Off the shelf", big valves for 748's are just a bit harder to find.

**I could only find 37/32's for my Corse heads "Off the shelf", so the exhaust valves need to be turned down to 31mm.
A few years back (around 7 or so) you could find almost any size you could wish for without having then made to order.

Steve R

Imola

Mr.R wrotePersonally I'd go with 888/916 heads* and skim them after the work on the chambers, (I can get a pair of heads accurately skimmed for £30) but you crack on chap. *Oversize valves are still available for these heads**, but they're getting harder to come by "Off the shelf", big valves for 748's are just a bit harder to find. **I could only find 37/32's for my Corse heads "Off the shelf", so the exhaust valves need to be turned down to 31mm. A few years back (around 7 or so) you could find almost any size you could wish for without having then made to order. Steve R

I would of gone with 916/888 heads but at £140 the 748 job lot was to hard to not snap up Mate.
It will get a motor running and get the bike on the road.
Have you found a spare 916 cylinder/barrel ? I have had no luck in finding anything 916.
I bought a 916 sp early crank with rods off Rich at louigi moto.

Steve

PTwo

marvin wroteYes, The pic on the left is my head.

Marvin, what kind of tool do you suggest I use to do some work like this? Is the small Dremel adequate? What about which tips to use?

Thanks,
Peter

marvin

Peter,

I used a pneumatic die grinder with 1/4" shank carbide burrs and sanding discs.

One lf those toy Dremel's would probably work but would be very slow IMHO

For the fine detail I used a Foredom Flexible Shaft Machine with small sanding discs. I don't own a dremel

brad black

i use one that looks like this in a bosch industrial electric die grinder, spins at 26,000 or so rpm. can be amazingly delicate.

http://www.suttontools.com/products/aluminium-cut-carbide-burs-tree-shape-radius-end-6mm-shank-b319/

chris steadman told me to take out the ridges between inlet and exhaust, but not open around the inlets as such. what i do for the 853 kits is here:

http://www.bikeboy.org/748with853kit.html

748 ports seem to work very well at the 850cc level, not sure about 900 something though.