Valve lash for early SF

E

eabergman

Full member
Poking through the Green Book I noticed a comment that some early 750SFs should have greater valve lash on the exhaust valves, 0.25 mm instead of 0.20 mm, but Tim doesn't mention how to know which bikes that applies to. I suspect it may be the ones that have the 4S cam (like my '71). Or is there some other determinant?
 
TAPPETS:  INTAKE      - .15mm or  .006?
                EXHAUST  - .20mm or  .008?

It's best to measure between the Cam Follower on the Cam Lobe Base (Heel) rather then on the Tappet nut as it's concave and results for inaccurate readings with a feeler gauge.

If you can mount a Dial Indicator on the Tappet Adjustment Bolt - All the power to Yah!

I ride a 71SF.

----------------

PS: You gotta fabricate your feelers to reach.
 
It's best to measure between the Cam Follower on the Cam Lobe Base (Heel) rather then on the Tappet nut as it's concave and results for inaccurate readings with a feeler gauge.
Click to expand...

Don't agree with you on that. Just had a look at a rocker.
1.) Distances from the axle to the tappet and the contact area on the
    follower are different.
2.) Cam lobe and follower are not flat, too. So where's the advantage?
3.) Should be very complicated to measure.
4.) On the dial indicator you'd read the lift on the tappet side, but not the gap.

Ernesto
 
I think Clay was referring to overcoming the problem of concave valve tips, where the valve adjusters have buried themselves into the valve tip making a feeler gauge useless in checking clearance. It is not so uncommon on any bike with those simple adjuster screws, not just Laverda Breganze twins. Yes you can sit a dial gauge onto the top of the adjuster screw. I know someone who simply uses the pitch of the adjuster screw and screws it out accordingly (e.g. if a screw has 0.50mm pitch you will get 0.25mm at half a turn out etc). The problem is avoided by doing a bit of mod and fitting adjusters from e.g Rotax 600 with the floating ball end that have a flat bearing on the valve tip. I know a few SF with this mod.
 
Tippie said:
I think Clay was referring to overcoming the problem of concave valve tips, where the valve adjusters have buried themselves into the valve tip making a feeler gauge useless in checking clearance. It is not so uncommon on any bike with those simple adjuster screws, not just Laverda Breganze twins. Yes you can sit a dial gauge onto the top of the adjuster screw. I know someone who simply uses the pitch of the adjuster screw and screws it out accordingly (e.g. if a screw has 0.50mm pitch you will get 0.25mm at half a turn out etc). The problem is avoided by doing a bit of mod and fitting adjusters from e.g Rotax 600 with the floating ball end that have a flat bearing on the valve tip. I know a few SF with this mod.
Click to expand...

Lee,

I tried those adjusters many years ago when I first found they would fit the Laverdas.  Not much luck though, the floating bit quickly shattered and fell off.  Went through 2 sets before being totally fed up and reverting to the originals.  Perhaps they were from a bad batch?  The Rotax engine hadn't been on the market for long, fitted to KTM and Armstrong at the time.  Any experience with that?

piet
 
Good argument: Not saying valve tappet lash will suffice with a feeler gauge but cam to a rocker arm adjustment with a feeler gauge is more accurate and will last longer and give a 1000rpm advantage ;o)

A Dial Indicator on the Set Screw works over a feeler gauge on the set screw , as long as you can place a Dial Indicator on the Set Screw.

If you use feeler gauges on the tappet Set Screws of a Breganzue 750 SF, you can out as much as .010 to .020".

That's why I recommend the Cam Heel Lobe to Rocker Shaft Measurement with a Feeler Gauge measured at:

TAPPETS:  INTAKE      - .15mm or  .006?
                EXHAUST  - .20mm or  .008?
 
Piet, no experience with that. Both mine and another SF racebike here have been using them for ages with no problems and I know of several in Australia with the mod as well. We also first did them when the Rotax single came out and had the right thread for us. Can?t understand what might have caused all yours to fail. I had much more problem with soft valve tips, hence the modification.
Clay, as Ernesto pointed out the rocker arms are not symmetrical so setting heel clearance instead of at the valve tip will not give the factory?s specified clearance. The SF being what it is valve clearance is not a major issue unless it is too little, preventing oil getting in there to lubricate between heel and cam, or preventing the valve from closing. Click for inlet and clack for exhaust is the general rule is it not?, but factory spec is best.
 
Rocker ratio is 1:1.125 I seem to remember - so any measurement between cam and heel would have to allow for this as already said. Makes Ron's quoted measurements incorrect - can't see where the extra 1000RPM comes from - perhaps Ron can explain for us?? - Regards - Phil
 
sfcpiet said:
Lee,

I tried those adjusters many years ago when I first found they would fit the Laverdas.  Not much luck though, the floating bit quickly shattered and fell off.  Went through 2 sets before being totally fed up and reverting to the originals.  Perhaps they were from a bad batch?  The Rotax engine hadn't been on the market for long, fitted to KTM and Armstrong at the time.  Any experience with that?

piet
Click to expand...
Piet, I think I was a first-in with this mod - probably early 80s. As soon as I saw the tappet screws on the KTM Rotax and discovered they were a matching thread I made the switch - have done so many km and some serious high rpm work (can't make an estimate - no speedo!), but also made this mod to two other SFs and not one failure. On the thick cast SF1 rockers I needed t grind a fair bit from the underside of the tappet end, but hasn't been a prob. SF2 and later 'thin-web'  :D rockers are a breeze. It's so nice to pull one out and see a still smooth valve tip.

I think I saw a similar fitment on a race Yamaha XS 650 project on an Oz forum. Wasn't the Rotax, but some other similar - may or may not have been same pitch.
 
Hi, whats involved in fitting these to rockers ? do the rocker arms need to be removed i presume ?? ;) , are they a KTM part ? or Rotax ? any part numbers ?, thanks , Bert.. 8)
 
Thanks for the clarification Grant, apologies to Ron and Clay.
Bert, Not sure what exact model but the first KTM that came with the Rotax 4 stroke with belt camdrive was what I ordered, and as Piet says there were numerous makes with that motor.
Yes it is a job to do when the head is off and the rockers out at least. On the later rockers I had to relieve a mm or two from the underside and I also tipped off a mm or two from the valve tip. You can see what needs when you have it apart, but it wasn?t a big job. IIRC the screws were pretty long and were cut off and a new square filed on for adjusting. Maybe there were a batch of soft tipped valves doing the rounds but it seemed fairly common for the valve tips to suffer over time with the original type adjusters back then.
Piet I do seem to remember that the later valve spring Ducatis had this form of adjuster, which were prone to falling apart.
 
Lee,

Definitely KTM/Rotax parts at the time, KTM had just started switching to 4-strokes with the Rotax OHC engines.  Not aware of any Ducatis using anything similar, always tried to steer well clear of them. :D

Yes, mid-80s and just getting into Laverdas, was suffering from valve tip wear as well as knackered rockers.  Didn't know half as much as today and made lots of (expensive) mistakes! ::)

Still got a set of those adjusters in my stash, inclined to give them a try in my next motor.

piet
 
Rocker ratio is 1:1.125 I seem to remember - so any measurement between cam and heel would have to allow for this as already said. Makes Ron's quoted measurements incorrect - can't see where the extra 1000RPM comes from - perhaps Ron can explain for us?? - Regards - Phil
Click to expand...

Yes you are correct Phil. I forgot about the Rocker Ratio.
Got CRAFT disease in my old age ;o)

X/.15mm = 1/1.125 where X = .133mm on the heel of the intake  cam lobe
or
x/.006" = 1/1.125 where X = .0053" on the heel of the intake  cam lobe

and

X/.20mm = 1/1.125 where X = .177mm on the heel of the exhaust cam lobe
or
X/.008" = 1/1.125 where X = .0071" on the heel of the exhaust cam lobe

What mean by an extra 1000 rpm; a SF motor with outta spec tappet adjustment will not rev much more then 6500 rpm but with proper adjusted tappets it can rev to 7500 rpm before complaining.

From my observations of the cam lobe surface on the SF is that they are flat and not tapered. Granted if a rocker bushing is worn it may have the tendency to bevel the contact surface of the cam follower.

That KTM Rotax tappet modification of Piranha's sounds great.

 
Tippie said:
..  Not sure what exact model but the first KTM that came with the Rotax 4 stroke with belt camdrive was ...
Click to expand...
now that brings back a few memories,,  sounds like the KTM with 560 Rotax that got flogged mercilessly around Lakeside harassing a Ducati 600 TT amongst others.
Now that was a lot of fun.  & a bit/lot scarey with the standard enduro single front disc.  :o
07-%20KTM%20560%20x_01.jpg

& I must be getting elderly, as have no recollection what adjustment was on those 4-valve head rockers.

I do remember the Triumph Trident rocker adjusters, long story but me mate had one, and I thought they had what we called an 'elephant foot' adjuster? 
But maybe it was after-market? 
elephant-feet-300x199.jpg

http://cylinderheadshop.com/elephant-foot-tappet-adjusters/

As I read Norman Hyde talks of a standard 'captive half-ball' adjuster as like the Ducati.  Maybe that's an elephant foot?
Apparently Norman Hyde has sold bucket loads of his mushroom head adjuster.
NormanHyde-tvt11.jpg

https://normanhyde.co.uk/meriden-triumph-bsa/mushroom-head-adjusters-long.html
I can see some merit in the mushroom head adjuster.  It is simple and looks bullet-proof.
NormanHyde-adjuster.jpg


yea, i've also found the click & clack method a good guide as to what's happening.
Tippie said:
.. Click for inlet and clack for exhaust is the general rule is it not?, but factory spec is best. 
Click to expand...

Ok.  As you were ,,
cheers,  Mark
 
markQLD said:
I do remember the Triumph Trident rocker adjusters, long story but me mate had one, and I thought they had what we called an 'elephant foot' adjuster? 
But maybe it was after-market? 
elephant-feet-300x199.jpg

http://cylinderheadshop.com/elephant-foot-tappet-adjusters/

As I read Norman Hyde talks of a standard 'captive half-ball' adjuster as like the Ducati.  Maybe that's an elephant foot?
Apparently Norman Hyde has sold bucket loads of his mushroom head adjuster.
Click to expand...


I had one of those elephant's foot adjusters let go in my Hurricane earlier this year. Engine dropped down onto two on the way back from Proserpine and when I got home found the centre inlet rocker had jumped the pushrod. When I popped the rocker cover off I almost shat myself when this little ball bearing rolled out and fell on the floor: wtf?  :o :o


Turns out the valves were supplied in two lengths and, as a consequence, so we're the threaded adjusters. Needless to say I could only get the mushroom adjusters in one length ("sorry Sir, we only sell them as a set.." ) and so had to change out all the valves. Might as well do the springs whilst I'm there etc.. That single Elephant's foot thingie turned out to be damned expensive: hopefully I'll never see another...


They weren't standard: just an 80s fad.. ::)

 
http://www.ebay.com/itm/New-Genuine-Rotax-Aprilia-Valve-Adjusting-Screw-AP0240205-/170897733873
Looks like one of the little devils
You were having a heap of fun there Mr Muir :-)
 
I run a Rotax 640 in my modified Armstrong. In the UK Gary at Sportax can supply the part mentioned:

http://sportaxracing.co.uk/shop/valves-rocker-arms/item-10-tappet-240-205/

Stuart
 
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