stiglarsenDK
Whats the story with the 748RS heads... do they go on a 888 Engine or not ?
I know that they have some nice 36mm Inlet valves, but shorter stems? But do they share rockers, and the rest of it ?
Grazie mille
STIG
marvin
I think they are like regular 748 heads as far as rockers and fitment. I put 748 heads on my engine years ago(standard 748 heads). Had to open the combustion chamber up (unshroud the valves, make same diameter as pistons/cylinder bore). Had 12.3/1 compression with stock 748 valves, 1mm squish
Ducal
Stig check out the guy over here with the Race Mongrel 748 851 in projects
huit
The only difference is the rocker covers are different to accommodate the shower injectors.
I have a set, put them beside my 97sp heads can't tell the difference.
seven4nineR
Hey Stig,
Neil Spalding of Sigma Performance has written quite an informative write up about the 748RS vs 748R here:
http://www.sigmaperformance.com/748r-748rs.html
There's some great info on the heads in relation to the very prescriptive Supersport rules at the time. There is a statement in the rules:
"01.58 DISCIPLINE SPECIFICATIONS - SUPERSPORT
EVERYTHING THAT IS NOT AUTHORISED AND PRESCRIBED IN THIS RULE IS STRICTLY FORBIDDEN"
And from what I can see the rockers are not mentioned so they must be OEM 748R.
stiglarsenDK
Thanks guys.. ill have a pro getting them ready for action..
griff851
Memory stretch, but something was not as wide as a standard 748. I do know that they seem to chew rockers with the r cams. We put it down to really high valve acceleration during a "why is it so" session. Also cam nuts were loose on everyone that came in according to bob, I only ever worked on one. bob did have a collection of heads we use to drag out when contemplating all that port combustion chamber shape stuff. Actually pretty cool with 851, 916, 916sps, 748 standard/drop cam/RS, 998 and monster S4R. Just looking and seeing what our little Italian mates were thinking.
stiglarsenDK
griff851 wroteMemory stretch, but something was not as wide as a standard 748. I do know that they seem to chew rockers with the r cams. We put it down to really high valve acceleration during a "why is it so" session. Also cam nuts were loose on everyone that came in according to bob, I only ever worked on one. bob did have a collection of heads we use to drag out when contemplating all that port combustion chamber shape stuff. Actually pretty cool with 851, 916, 916sps, 748 standard/drop cam/RS, 998 and monster S4R. Just looking and seeing what our little Italian mates were thinking.
I have read that the 748RS ran some special belts (wider) .. not sure why .. ?
marvin
Back before I purchased my V2 604 cams (SPS equiv.) I looked into running other cams, ( 748 RS I believe) for either the intake or exhaust(don't remember whether it was an intake in place of the exhaust or visaversa) and found out that one had to narrow one of the cam lobes because it fouled the rocker arm. Supposedly in that application very close or the same as a SPS cam
(Brad will know!)
griff851
Your right Brad will know. Pretty sure it was in the casting. Bit of bastard, I can picture the head and looking at ports and rocker pin mounting. I think Marvin is on the right track.
hauge
I have an 748R
I think the only difference from an RS is the cam shafts (more duration, same lift).
I had mine 748R as a track bike for a long time (its retired now) and it made more than 12000 km on trackdays. Had to replace three rockers when I bought it. There after none rocker had to be replaced...
It have wider belts.
I have a spare set of complete 748R heads if someone is interested...
griff851
Ah ha, could handle it any longer so rang bob. Valve centres are different. The 748r and Rs have shorter distance between inlet and exh valve centres.
jakepeewee
I think only the distance of the valve centers of the inlet valves of the 748R is a tiny bit smaller. So the center of the 748R inlet camlobes also differs. Exhaust valve centers are no different than on other desmo Quattro heads.
griff851
Yep that's it. 😄
jakepeewee
I recently measured the different valve centres.
Desmoquattro 'standard' inlet valve centres: 41,1 mm ( as measured from my 851SP3 heads)
748R inlet valve centres: 39,35 mm
Distance between inlet valves is reduced by 1,75 mm for the 748R.
stiglarsenDK
Does this mean that i can't use SPS , G cams etc for these heads ? Rockers are the same or ?
grazie mille
hauge
hmm.
I used 748R cams in a 96 engine. Never thought they would be different.
jakepeewee
I think the difference between the valve centres is so small that using G-inlets should not be a problem.
I was planning to do the same (G-inlet cams in 748R heads), but then decided to use 748R cams. Not because of this potential problem but because of the different characteristic of the cams.
