Volki
Senior member
- Location
- near Cologne
Laverda Parts
- Thread starter Volki
- Start date
Dellortoman
Hero member
- Location
- Tasmania, Australia
This could be a stupid question, but what are the round white plastic things? They don't look like anything that's on my Jota.
They actually look like pulley sheaves that you'd find on a sailing boat.
They actually look like pulley sheaves that you'd find on a sailing boat.
motoddrob
Hero member
- Location
- S/W Australia
750 cam chain guide and tensioner Cam
Dellortoman
Hero member
- Location
- Tasmania, Australia
OK. I thought it might be something to do with a 750. Their insides are a mystery to me.
piranha-bro2
Hero member
- Location
- Melbourne
Hoping to source a primary chain tensioner in Oz - shipping makes it a not-worth-it exercise.
breganzane
Hero member
- Location
- NSW Australia
You're handy with a lathe are you not? Last one I needed to replace I just made one up, I've also made camchain ones about 10mm smaller so that the overly-tight chains join up easier when new.
Dellortoman
Hero member
- Location
- Tasmania, Australia
Ooh, 10mm smaller wouldn't pass the rivet counter test Steve, unless you're trying to replicate a worn one.
What species of plastic do you use Steve (assuming you use plastic)?
My Kawasaki has a plastic sprocket as a cam chain tensioner wheel. I dunno what kind of plastic it is but the bloody thing wears away at a prodidgious rate. Last time I replaced one (was not actually on my bike that time), I considered making a new one out of steel, or maybe bronze, but I didn't have the equipment to cut the sprocket teeth. Maybe Kawasaki (and Laverda) chose plastic so it's sacrificial and doesn't wear the chain.
What species of plastic do you use Steve (assuming you use plastic)?
My Kawasaki has a plastic sprocket as a cam chain tensioner wheel. I dunno what kind of plastic it is but the bloody thing wears away at a prodidgious rate. Last time I replaced one (was not actually on my bike that time), I considered making a new one out of steel, or maybe bronze, but I didn't have the equipment to cut the sprocket teeth. Maybe Kawasaki (and Laverda) chose plastic so it's sacrificial and doesn't wear the chain.
Basketcase
Senior member
What plastics are suitable for the 750 camchain tensioner ?
I reckon Ertalyte would be a good candidate due to its low friction and easy machinability.
I reckon Ertalyte would be a good candidate due to its low friction and easy machinability.
piranha-bro2
Hero member
- Location
- Melbourne
How do i use my lathe to make one of those slipper primary chain tensioners with the rubbery coating, Steve?! Maybe the old GT style ones with the roller but not mine. Is it possible to have the coating replaced on a worn one? If Red's guy can make kevlar clutch plates surely this is doable?
A friend's old man made some cam chain tensioner wheels out of some white nylony stuff but I never trusted it and went with SFC needle roller versions. I need an SFC cam chain guide wheel now, actually but they seem a bit hard to find - I could machine the middle out of the NOS SF ones I have but the wheel is waisted on those - could made the centre boss from alloy wider and freeze a ring on the open side, but prefer to just buy the SFC one. I have four needle rollers for them - that's the easy bit!
motoddrob
Hero member
- Location
- S/W Australia
somewhere amongst my stash of parts I'm fairly certain I have a metal version with sprocket teeth. Came with a bunch of spares I brought back in the 70s.
hooksey
Hero member
- Location
- Vic , Australia
CLEMTOG
Hero member
nice job hooksey, longevity? how many clicks so far and what is the damage?
AFAIK (what the hell DIK) the guide/tensioner wheels on 750's are plain when new, and get to show "teeth" after a fair bit if use, dont know where the plastic shards go mind (eek!)
I have NOS primary tensioners if any one needs one, and with a tiny mod they work on triples
CLEM
AFAIK (what the hell DIK) the guide/tensioner wheels on 750's are plain when new, and get to show "teeth" after a fair bit if use, dont know where the plastic shards go mind (eek!)
I have NOS primary tensioners if any one needs one, and with a tiny mod they work on triples
CLEM
MarnixSFC
Hero member
You mean the toothed tensioner wheel for the camchain, Rob? Found one in a 1974 SFC with various factory racer parts. Bit of a crude creation, but works fine.
Marnix
martymoose
Hero member
- Location
- Sydney, Australia
Pretty sure Brett's got them in club spares Q, ex Wolfgang.
piranha-bro2
Hero member
- Location
- Melbourne
Oooh! Nice tip, Marty. I must hassle the man then. Am I to believe that triples and twins have slightly different tensioners?
BTW Clem, those bits of nylon that used to be part of the smooth cam wheels can end up in the rocker spindles and from there block the oid ways that spray the cam from the underside of the rocker - expensive nylon chips and splinters is what it becomes then! Plenty of it in the mesh of the oil strainer too, which is why I like to remove it rather than rely on a drain plug only. Even now I have. redax drain plate I'll still pull it out every 2 or 3 oil changes to check and clear.
I have something similar to the pic Hooksy put up of a Primary Chain tensioner that is fitted near the swingarm and acts as a drive chain guide on the 530 chain. It does a good job of keeping the final chain away from the engine case. I bought it off some bloke whose contact details were in an article in Classic Bike. The original plastic bit has rubbed through so I made a couple of replacements bought from a Plastics supply place near me. It's not perfect but works well enough to stay fitted for 10 or so years. Maybe someone from England knows who this was back in the day.
Never seen a bit of nylon in the oil strainer on any of my 750s even though when I changed the cam tensioner wheel on my SF2, there was hardly any left.
Paul
hooksey
Hero member
- Location
- Vic , Australia
Put rnd 10k on mine before i sold said bike. A mate of mine had a few made up in the 90's and he has had one in service for rnd 60k, no discernible wear. Some sorta Nylon..... hard as a cats head
Dellortoman
Hero member
- Location
- Tasmania, Australia
Yes. Triples have a curved tensioner blade for the cam chain. No rollers.
That's what used to worry me about the disappearing plastic tensioner sprockets in my Kawasaki, but at least that bike has a decent cartridge type oil filter.
Dellortoman
Hero member
- Location
- Tasmania, Australia
Seems to me that this is something that can be improved upon.
A steel idler sprocket is a much better engineering solution as a chain tensioner idler than a cylindrical plastic roller. Steel idler sprockets are not unusual as chain tensioners in many applications, including timing chains on engines.
A cylindrical roller will bear on the side plates of the chain, until the side plates cut grooves into the roller, which would probably happen quite quickly with a plastic roller. Then the tensioner roller will then bear on the chain rollers and the wear rate will slow down. Eventually the chain could wear corrugations resembling sprocket teeth into the tensioner wheel, as Clem observed above. So why not start with a sprocket in the first place to avoid all this bedding in and constant re-tensioning as a result?
Plastic idler sprockets running in hot engine oil don't last long in my experience. A steel sprocket would have a greater service life and shouldn't wear the chain any more than the crankshaft and camshaft sprockets, and it'll maintain constant chain tension way longer than anything made of plastic. Actually, I strongly suspect (for a number of reasons) that it would be easier on the chain than a plain roller. The Laverda 750 cam chain is massively over-engineered anyway.
If anyone can provide an explanation as to why a plastic roller is preferable, I'd be happy to learn something new. A few arguments I can think of are noise reduction, shock absorbtion, low friction and cost reduction. None of which are compelling reasons in my opinion. I suspect Laverda chose to go with a plastic roller for no other reason than cost management.
If I had a 750 that needed a new tensioner, I'd buy an industrial sprocket blank of the right size and bore it to suit the needle roller.
I dunno what size sprocket would be required if anyone wants to do this. I believe the chain is an 06B duplex. If someone can tell me the tensioner roller diameter, I'll work out the equivalent sprocket size.
Sourcing a sprocket shouldn't be a problem. An industrial type would be perfectly adequate. There's bugger-all load on the teeth because the chain isn't transmitting any power to the sprocket. It's just an idler.
Duplex Sprockets 06B-2 with hardened teeth - English
ISO-Nr.: 06 B-2 (3/8“ x 7/32“) pitch: 9,525 mm inner width: 5,72 mm roller-dia.: 6,35 mm Tooth width bf2 15,4 mm ba 1 mm (radius width) rx 10 mm (min. tooth radius) hardened teeth (45-55 HRC) No. of tooth pitch … Weiterlesen →
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