Advice please
- Thread starter julian
- Start date
MarnixSFC
Hero member
Julian,
The pistons sounds a bit like the Electronica SFC piston. In a further standard setup, they lower the compression..
The clutch is the older type with steel hub and the pins. Better use the later type.
Regarding single camchain, the 73 SFCs didn?t run too many races, but at Imola one of those single cam chain snapped and Laverda quickly returned to the duplex setup.
Marnix
The pistons sounds a bit like the Electronica SFC piston. In a further standard setup, they lower the compression..
The clutch is the older type with steel hub and the pins. Better use the later type.
Regarding single camchain, the 73 SFCs didn?t run too many races, but at Imola one of those single cam chain snapped and Laverda quickly returned to the duplex setup.
Marnix
Laverda SF
Hero member
Along with all the expert advise from fellow members regarding the Breganze 750, if you're seriously thinking of gaining more revs and Hp from a SF, I suggest you read my replies to this thread Titled: Valve Seat Angles small valve 750: http://www.laverdaforum.com/forum/index.php?topic=84097.0
Follow the Jenken Valve Seat Design using lighter larger Valves and heavier Springs, the cam choice is yours.
The SF Avatar you see to your left has no problems spinning 8G's with STK open VBH 30A's, Pistons, and Cam.
Follow the Jenken Valve Seat Design using lighter larger Valves and heavier Springs, the cam choice is yours.
The SF Avatar you see to your left has no problems spinning 8G's with STK open VBH 30A's, Pistons, and Cam.
Hi Marnix,
The pistons "look" like they would give a much higher CR than the ones I took out of my other slightly later engine, the crown height is the same but the dome is much larger! However I don't know what CR the other pistons were so you could be right! not that it matters as they will go in the bin anyway, it was just rather interesting. Maybe I will measure the CR and take some pics.
Will get my self a new clutch then ;o) had my thoughts that I would be told this! Did they have problems or was it just an update?
SF,
8k on my engine would be a short fuse I am afraid, as the stroke will be 87mm and the piston speed and acceleration would be past what I would call a sensible limit for general use! my max will be 7500 ish.
Head work will be done on my flow bench and we have a valve seat cutting machine etc so can do all in house, Inlet valve sizes will be 42 or 44 but will test both before deciding for sure, I am a strong believer in "small plugs in big holes" so will see what happens during tests.
Like I said before, carbs will be either 39 or 40mm Dellortos.
Cams, not decided yet, will depend on how well I can get the head to flow.
Anyone got any experience with Megacycle cams?
Julian
The pistons "look" like they would give a much higher CR than the ones I took out of my other slightly later engine, the crown height is the same but the dome is much larger! However I don't know what CR the other pistons were so you could be right! not that it matters as they will go in the bin anyway, it was just rather interesting. Maybe I will measure the CR and take some pics.
Will get my self a new clutch then ;o) had my thoughts that I would be told this! Did they have problems or was it just an update?
SF,
8k on my engine would be a short fuse I am afraid, as the stroke will be 87mm and the piston speed and acceleration would be past what I would call a sensible limit for general use! my max will be 7500 ish.
Head work will be done on my flow bench and we have a valve seat cutting machine etc so can do all in house, Inlet valve sizes will be 42 or 44 but will test both before deciding for sure, I am a strong believer in "small plugs in big holes" so will see what happens during tests.
Like I said before, carbs will be either 39 or 40mm Dellortos.
Cams, not decided yet, will depend on how well I can get the head to flow.
Anyone got any experience with Megacycle cams?
Julian
Julian,
All cases will accept grooved balls for the LH main, later cases had an additional groove machined to accept a wider retaining half-ring on the outside of the roller bearing. Was standard practice from then on, the first, now unused, groove remained though.
A larger crank sprocket was never avaialable, same teeth count and pitch as the triple, only different sideways spacing. Because the 750 clutch sprocket is smaller but the shaft distance greater than on the triples, the same chain fits both.
Keith may still have some #530 18T front sprockets, saves you going much larger on the rear. (I prefer the small rear sprocket look, saves weight too!
)
Haven't had good results from 44mm inlets, at least not in a stock type head. Need to be recessed far into the head to attain a seat at all and for clearance to the liner, comp drops dramatically as well as flow going down the drain. I'd stay with pretty much stock valve sizes, optimise the ports at the seats and immediately before, and look for more valve lift. Try to keep the valve head as far as possible in the combustion chamber. Don't expect too much from the head, pretty crappy to begin with... but small improvements go a long way!
As Marnix stated, hi-domed pistons might well be SFC items intended to fit liners without spigots and the corresponding head. Will then work properly.
Clutch set-up is the earlier type, steel clutch hub, too fuckin' heavy.! Swap for the later alloy type, not many clutch plates around to fit the earlier type anyway.
Seems you've found yourself a pair of old dogs as a basis!
Know of one SFC that's been run with a single-row cam chain for the past 15 years without issues. Perhaps the factory just had bad luck at Imola '73.
piet
All cases will accept grooved balls for the LH main, later cases had an additional groove machined to accept a wider retaining half-ring on the outside of the roller bearing. Was standard practice from then on, the first, now unused, groove remained though.
A larger crank sprocket was never avaialable, same teeth count and pitch as the triple, only different sideways spacing. Because the 750 clutch sprocket is smaller but the shaft distance greater than on the triples, the same chain fits both.
Keith may still have some #530 18T front sprockets, saves you going much larger on the rear. (I prefer the small rear sprocket look, saves weight too!
)Haven't had good results from 44mm inlets, at least not in a stock type head. Need to be recessed far into the head to attain a seat at all and for clearance to the liner, comp drops dramatically as well as flow going down the drain. I'd stay with pretty much stock valve sizes, optimise the ports at the seats and immediately before, and look for more valve lift. Try to keep the valve head as far as possible in the combustion chamber. Don't expect too much from the head, pretty crappy to begin with... but small improvements go a long way!
As Marnix stated, hi-domed pistons might well be SFC items intended to fit liners without spigots and the corresponding head. Will then work properly.
Clutch set-up is the earlier type, steel clutch hub, too fuckin' heavy.! Swap for the later alloy type, not many clutch plates around to fit the earlier type anyway.
Seems you've found yourself a pair of old dogs as a basis!
Know of one SFC that's been run with a single-row cam chain for the past 15 years without issues. Perhaps the factory just had bad luck at Imola '73.
piet
Andy,
Always considered the duplex timing chain a bit of an overkill in this particular engine.
But then, they seem to last forever, at least far longer than the majority of cams and rockers!
19T gearbox sprockets still in good supply, 18T was used for the US to raise revs a bit in order to keep the battery charged during tootling around at 55mph.
piet
Always considered the duplex timing chain a bit of an overkill in this particular engine.
But then, they seem to last forever, at least far longer than the majority of cams and rockers!
19T gearbox sprockets still in good supply, 18T was used for the US to raise revs a bit in order to keep the battery charged during tootling around at 55mph.
piet
phil37
Hero member
- Location
- Lincolnshire
Julian - Not sure if this is relevant - but if the 4000 series motor only has one bracing "fin" from the crankcase to rear of barrell - do choose your later one as you will be going into realms where crankase strength may become more of an issue. i do have only one fin on my 2000 series proddy racer motor that has run 11.8:1 for some time - but it is only a 750cc motor. If your 4000 series motor already has the 2 fins - please disregard this posting - Regards - Phil
Dellortoman
Hero member
- Location
- Tasmania, Australia
andychain said:
Problem is that it's a fixed shaft centre distance selected for the standard chain configuration so there's no slack, and therefore very little deflection at the tensioner shoe. If you change the number of teeth on the front sprocket, you'll have to change the number of chain links and end up with a lot of deflection at the tensioner.
Far better to alter gearing at the rear wheel chain drive.
Cheers,
Cam
andychain
Hero member
You might be surprised, with 1 tooth difference you can usually get away with the same length of chain.
I have always reduced my rear on Bandits by 3 teeth and get the standard length.
Another reason to use non O ring where crank links are still available (1 pitch). With O ring you can only shorten and lengthen by 2 pitches.
Every show somebody will ask for O ring crank links.
For the racers out there using 520 Japanese I have some cranks for 520 that fit the RK 520 (thicker plates).
Andy
I have always reduced my rear on Bandits by 3 teeth and get the standard length.
Another reason to use non O ring where crank links are still available (1 pitch). With O ring you can only shorten and lengthen by 2 pitches.
Every show somebody will ask for O ring crank links.
For the racers out there using 520 Japanese I have some cranks for 520 that fit the RK 520 (thicker plates).
Andy
Hi Guys,
Again, thanks for all of your efforts!
The engines I have, both have the double strengthening ribs, 8274 is from my complete bike and seems to be standard and all stock with nothing strange.
4156 was a complete engine I picked up especially for the 1000 project bike. I did check for the second rib but thanks for mentioning it! The rest is a kit of bits made up as I go along, OR "Make-ing" up as I go along.
This engine is the one with the early clutch and strange pistons.
The reasoning for the larger engine sprocket was to give the clutch an easier time! (increase it's revs compared to the engine and torque at the clutch goes down of course) I can get it back at the rear wheel with the rear sprocket. Going for the flat track look so it "HAS TO HAVE" a biggy
If no room for a larger front (I didn't check Paul ;o) the I can always make a new clutch sprocket. We will see. Maybe I don't need to worry?
Piet,
I thought the same with 44mm valves, it looks like the head will probably not benefit from these. As I say, "Big holes, small plugs" except in bed
Cam suppliers? Availability?
Again, thanks for all of your efforts!
The engines I have, both have the double strengthening ribs, 8274 is from my complete bike and seems to be standard and all stock with nothing strange.
4156 was a complete engine I picked up especially for the 1000 project bike. I did check for the second rib but thanks for mentioning it! The rest is a kit of bits made up as I go along, OR "Make-ing" up as I go along.
This engine is the one with the early clutch and strange pistons.
The reasoning for the larger engine sprocket was to give the clutch an easier time! (increase it's revs compared to the engine and torque at the clutch goes down of course) I can get it back at the rear wheel with the rear sprocket. Going for the flat track look so it "HAS TO HAVE" a biggy
If no room for a larger front (I didn't check Paul ;o) the I can always make a new clutch sprocket. We will see. Maybe I don't need to worry? Piet,
I thought the same with 44mm valves, it looks like the head will probably not benefit from these. As I say, "Big holes, small plugs" except in bed
Cam suppliers? Availability?
phil37
Hero member
- Location
- Lincolnshire
Hi Julian - have used 44mm inlets on my 870cc - I realised that they would suffer from shrouding as they had to be moved back in head to get enough seat area. I then plunged in with a 50mm end mill (with radius on cutting teeth) slightly offset towards the middle of head. I then spent a lot of time blending and rounding the edges into skull to drastically reduce/remove any shrouding effect -shame i never took any photos of it at the time. - Regards - Phil
phil37
Hero member
- Location
- Lincolnshire
Be careful where you stick it Julian 
Julian,
You can forget a larger crank sprocket... had a close look today, not much space left till the chain fouls the oil pump. Maybe 2 or 3 teeth more possible, probably not really worth the hassle. Not so easy to decrease the clutch sprocket either without a complete re-design.
piet
You can forget a larger crank sprocket... had a close look today, not much space left till the chain fouls the oil pump. Maybe 2 or 3 teeth more possible, probably not really worth the hassle. Not so easy to decrease the clutch sprocket either without a complete re-design.
piet
Hi Piet,
Yes, looked last night and dead right! not much room to play with on either.
Also checked my funny pistons and Marnix was absolutely spot on!
So will just have to make sure the clutch is as strong as possible. Have been chatting with Keith and maybe he has some Kevlar plates for me.
Told you I had better be polite on here
Just doing an interesting starter motor conversion, hope it works and will show you after the weekend.
Julian.
Yes, looked last night and dead right! not much room to play with on either.
Also checked my funny pistons and Marnix was absolutely spot on!
So will just have to make sure the clutch is as strong as possible. Have been chatting with Keith and maybe he has some Kevlar plates for me.
Told you I had better be polite on here
Just doing an interesting starter motor conversion, hope it works and will show you after the weekend.
Julian.
Hi,
Have a look at the pics and see what you think,
I had a Yamaha FZR750 starter lying around from one of my past projects and thought it would be a good weight saving trick.
It's "supposedly" more powerful and certainly showed it in bench testing with a torque arm test.
So, "of to work I go"
Cut down the old Laverda housing to the best length, did the same with the Yam front housing, welded them together, Fitted new bearing and oil seal, removed the armature, pressed out the shaft to shorten it, turned it down to push back into the armature to get the spline in the right place, modified the other end and cut it to length, turned the back out of the rear yam housing to weld in a new ally chunk to accommodate a roller bearing instead of the small std graphite one, shimmed it up and screwed it back together! Hey presto!
2725g all up weight against 3800g+ of the standard starter!!
I say 3800+ because my little engineering scales Err after 3.8kg
So a good Kilo weight saving! Cool.
Have a look at the pics and see what you think,
I had a Yamaha FZR750 starter lying around from one of my past projects and thought it would be a good weight saving trick.
It's "supposedly" more powerful and certainly showed it in bench testing with a torque arm test.
So, "of to work I go"
Cut down the old Laverda housing to the best length, did the same with the Yam front housing, welded them together, Fitted new bearing and oil seal, removed the armature, pressed out the shaft to shorten it, turned it down to push back into the armature to get the spline in the right place, modified the other end and cut it to length, turned the back out of the rear yam housing to weld in a new ally chunk to accommodate a roller bearing instead of the small std graphite one, shimmed it up and screwed it back together! Hey presto!
2725g all up weight against 3800g+ of the standard starter!!
I say 3800+ because my little engineering scales Err after 3.8kg
So a good Kilo weight saving! Cool.
