750sf3 Engine

sfcpiet said:
I never found out the real cause, Lee. 

Don't think the cam was too fierce or springs too hard, possibly a material issue.  The old Rotax bangers were top contenders for a while in the single road racing classes here, never heard of them having great reliability issues.  But, when they went, they went with a loud bang and a plume of smoke! :D

piet
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I had a lot of respect for those motors, had a customer with one (the one with the terrible WP suspension). Roller rocker arms!! Yes please!
 
I had never seen or heard of the wire on stud mod, but I can see it working and stopping a "seal" having been made by the studs finding its way to one side (for whatever reason) and blocking the cross chanell, I had in my mind when the thread opened a mental picture of spiral would wire all the way up the studs through the block and the head!

Now............ does anyone have a ready made picture of the factory race mod (yes really) of the cam chain wheels welded together at 120 degree intervals as precaution against loose, snapped or stretched pinch bolts?

CLEM
 
CLEMTOG said:
I had never seen or heard of the wire on stud mod, but I can see it working and stopping a "seal" having been made by the studs finding its way to one side (for whatever reason) and blocking the cross chanell, I had in my mind when the thread opened a mental picture of spiral would wire all the way up the studs through the block and the head!

Now............ does anyone have a ready made picture of the factory race mod (yes really) of the cam chain wheels welded together at 120 degree intervals as precaution against loose, snapped or stretched pinch bolts?

CLEM
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Can only imagine that to be a stop-gap measure during a race, Clem.  It would ruin otherwise fine parts and make removal a pita with possible damage to the head.  Don't think heads out of the competition shop grew on trees, not even back then!

The factory team would have had access to the best parts of all, and if they weren't available or good enough, they would have been made.

piet

 
I cant remember who told me about it, but it was done at the factory routinely, although that may have been only for a short period. After a race, remembering that they were 24 hour, non stop in those days, back at the factory the motor(s) would have almost certainly been dismantled in preparation for the next one, and the welds ground off and the chain wheels discarded, not really any need to be concerned about swarf as a complete strip would have been the order of the day, leather covers would have been used and the opportunity to wash everything, no need to replace the cam halves or the heads, only the chain wheels,

I think it must have been Ricardo Oro, who told me about thi, he once filed a stud thread off in situ for me that was causing the cam cover to bottom and he had a ready made piece of supple leather, with e square hole precisely cut to trap the swarf.

CLEM
 
A friend here who has prepared many race motors routinely put a tiny dab of mig weld on crucial nuts to prevent them loosening. He did it on the cam stud nuts of the SF motor he ran in a racing sidecar. As Clem says, it doesn?t take much to prevent the scrap of grindings getting where you don?t want them. I used his idea on the rear drum on my SF2 when the split pins started to have trouble holding it together, the alternative was replacing all the links and bushes, a job that went onto the back burner, and I can do whenever I have the time as I have a disc rear on the bike now.
 
Tippie said:
As you can see, it simply ensures peace of mind that the studs cannot be pulled in to block the oil from getting up/down the studs to the rocker pins.
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With the Wagner 880 kit, he recommends relieving the studs in this area. I?m pretty sure for this very reason. I could be wrong, but Red did it on mine, so he must be in the know.
 
Here's the gap in question, on a '73 works motor with 12mm studs.

Not the correct head unfortunately, "only" a later Eletronicca head. :D

piet
 

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This head was certainly modified to fit over the bigger studs.  I have reasons to believe this was done at the factory, or at least in colloboration with the factory.

Happy birthday BTW! :D

piet
 
sfcpiet said:
This head was certainly modified to fit over the bigger studs.  I have reasons to believe this was done at the factory, or at least in colloboration with the factory.

Happy birthday BTW! :D

piet
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Danke sehr.  (or dank you field mouse as my old dad used to say)

Paul
 
Hi Piet,
So the 73 works motor ran a single row cam chain chain, never knew that. Did the crank have a single row of teeth as well or did you use just one of the two?
 
Yes Rob, special crank as well.  So are the damper and tensioner wheels.  Primary drive was another deviation from stock, only a duplex chain without tensioner, only guide slippers.

The other pic shows the special conrods, the one in the foreground is the bastard that gave up... :'(

piet
 

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Hi Piet,

what was the nature of the failure? Fatigue of some sort?

Do you have an 'after' shot that you would care to share with us? It is fascinating to get a glimpse into a works motor.

Cheers,

bazzee
 
Hi Piet,
thanks for the photos. Having seen the motor in Sydney I knew it was special on the outside but didn't know how special it was on the inside. Interesting
 
motoddrob said:
Hi Piet,
So the 73 works motor ran a single row cam chain chain, never knew that. Did the crank have a single row of teeth as well or did you use just one of the two?
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And the very special low rocker head.
It's well detailed in the Isles-van der Schalk SFC book since a common friend in France had one and took plenty of pics of the inside before......it broke a rod.

Paul
 
Interesting that they went to all that trouble making the motor so special but didn?t provide for dialling in the cam timing. A shame they went just that bit too far with the rods, when std SFC rods seem to be so durable.
 
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