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Well I ordered some 1098 cams just to settle my curiosity! If it works, it works, either way I'm interested in some 999S cams. At the weekend I was explaining to a mate about another project that got sabotaged by covid. I bought an ST4S engine from a comrade in the UK. It's FINALLY here in Norway. The plan is to pull it to pieces and machine the swinging arm bosses to match my 748 frame, rebuild it with the usual work on the squish, cam timing and porting along with some reworked injector bodies (S4RS with pico injectors, either 4 or 12 holes) and build a hybrid wiring loom to use the 59M brain. He said "You would be just as well taking that racing with all the bits you have for it". Some people really know how to spoil your day! It's going to be a busy winter.
I couldnt descipher this part from norwegian to english with my swedish language set :) : He said "You would be just as well taking that racing with all the bits you have for it" Kan jag få det i rå norsk så fixar jag det säkert !
You could have had a couple of 1098 heads I swapped for part of a mapping job, with a noble goal I'd give them away.
Heads are up for grabs with proper motivation.
 

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Discussion Starter · #22 ·
Takk så mye for tilbudet men jeg tror jeg har nok prosjekter for den vinter. Min kamerat sagt at jeg burde bruke den 748 med ST4S motor på banen siden jeg har masse reservdeler. Den sykkel skulle ha c130 hester hvis jeg gjøre en god jobb. Uten en skikkelig kamaksel jeg tror det blir vanskelig å få over 130 fra 999en.

Hope that works, I'm from Skottland originally! The 1098 heads would probably be better on a big bore motor.
 

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If this is so I have a lathe and may be able to fix that
I have a lathe, too, but I'm pretty sure I'd "fix" em permanently! I admire those who can take on something like that! Good on you!
 

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99' 996
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Thats along the lines of what I was thinking. If the cams wont fit the head, will the head fit the motor? Wouldnt the 1098 have larger valves? More port volume? Seems like a double win to me.
 

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The issue for the heads will be stud spacing. Only the 999R has the same stud spacing as the XX98 and 848... if I remember correctly.
 

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Discussion Starter · #27 ·
The stud spacing is bigger on the 1098 but from what I can see that is not an insurmountable problem. The tricky bit would be keeping the belt alignment square. The valves as a couple of mm bigger on the 1098 but from the pictures Alexc kindly put up it looks like the lobe spacing on the camshafts are the same. It had occured to me to see if 1098 valves are the same length as the 999. A cheap job lot of cams are now winging their merry way to Norway for me to experiment with. They will test my skills on the lathe anyway.
 

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I bought a set of 999S cams a year ago on Ebay for ~$550. It was just a waiting game. Seems like a lot of work to go this other route, but if you've got a cold winter, space, and time, could be a fun challenge :cool:
 

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Discussion Starter · #29 · (Edited)
My job lot of cams arrived today. Bought them cheap for experimenting. Struck lucky in a way. There was an S vertical inlet cam and 1098 vertical inlet. After a bit of measuring it appears that it will be relatively simple to make the 1098 cam fit. Put simply, thinning the collar at the drive end bearing by 1mm should allow the 1098 cam to fit the 999. See photo at A.
Wood Gas Cylinder Auto part Art
 

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Discussion Starter · #30 · (Edited)
The cam lobes are 1mm further apart but centred the same on the cam. That means that the 1098 cam lobes are all 0.5mm outboard from the middle of the cam. Judging by the witness marks on the 999 cam this will not be a problem. If it is I'll take a closer look at the cam followers. I just hope the exhaust is the same. The difficult bit is going to be the machining. I ran a rat tailed file over the edge of the collar and was able to mark it so I may be able to cut it using the lathe tools I have. If necessary I will rig up a dremel to grind it. Later I'll compare the lobes.
 

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Discussion Starter · #31 ·
Well that torpedo's that plan! This photo shows the S vs the 7M3 inlet lobes.
Bicycle handlebar Bicycle part Suspension Table Automotive tire


Looks like I need S cams then. If the table on the Bike Boy site is correct then the rocker ratio is different between the 999 and the 1098 as this is the only way to get more lift. Oh well, nice try, no coconut!
 

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Discussion Starter · #34 ·
can you make an valve lift diagram? than you can see if the 1098 cams go with the 999 rockers.
I suspect the opening rocker shafts are at a different position in the head requiring different rockers.. If there is less valve angle but the rocker aksels are in the same place in the 1098 heads then this would require longer rockers too. If anybody has two heads to compare I would be interested to know the differences.
 
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