SF3 camchain

M

macavity99

Full member
Location
Bedfordshire, UK
Removed the cylinder head today. Nobody warned me that the front camchain end would leap off the sprocket and fall into the engine  :'(. The rear end is securely held by "iron wires" as recommended in the Laverda book. I can see the chain down the cylinder barrel tunnel.

Question 1: Will I be able to fish out the camchain when the barrel is off?

I want to order new piston rings from Wolfgang asap.

Question 2: Where do I find any markings on the pistons to identify whether standard or oversize?

Cheers

Steve in UK

 
Hi Steve
Been there, done that :-[ :-[ :-[
Yes, you should get it out ok, but it'll be easier with an assistant. I fished mine out with the barrels on.
You just have to make sure you get it back on without jumping a tooth on the lower sprocket.
The easy access through the sump plate will prove very useful!
Andy
 
Hi, Steve.

You'll find the size on the piston crown.
Has to be decarbonized to see something. Remove the pistons for that.
You'll find 80.0 for standard size, 80.4 for 1st oversize,
80.6 for 2nd.
Best to mildly hone the barrels when using new rings.

hth
Ernesto
 
this is a twin we are talking about,
so underside access is not trhough a cam chain pedestal door (as on triples), but through the centrally mounted oil sump strainer.

When you have fished the chain back up (with a wire) be sure that it is ACTUALLY on the crank shaft sprocket, and not running alongside it, because in this state the engine will run, but not for long, always, always, ALWAYS, use a torch, and if you dont have the motor out of the chassis, a mirror as well, and if you have removed head and barrell, with the motor in the chassis, then you have only two bolts remaning to drop the unit to the floor, and then lift it onto a bench,which will make all operations so much easier
CLEM
 
this is a twin we are talking about,
Click to expand...
When you have fished the chain back up (with a wire) be sure that it is ACTUALLY on the crank shaft sprocket, and not running alongside it, because in this state the engine will run, but not for long,
Click to expand...

Your 1st statement nullifies the 2nd Clem  :D :D - Regards - Phil
 
The barrels are coming off anyway, so I hope it will then be easy to retrieve the chain.

I haven't found any markings on the piston crowns. Does this mean they are standard size?

Cheers

Steve in UK
 
"nullified"
I wish you would talk proper estuary Phill
probably standard, measure the bore at the base under the piston (non swept area)
80mm = standard
oversize 80.4 or 80.8

96mm=taurauromerde

CLEM
 
Clem beat me to it

Steve, pick up a cheapo Chinese set of internal micrometers and a medium quality set of digital calipers. Measure the bore in several places, but you're most interested in the measurement as low down in the bore as you can get, and the measurement taken parallel to the crankshaft should be the closest to the original. You piston will obviously be slightly smaller than the bore dimension, but if the bore is less than 80.4 mm, it's probably standard, less than 80.8, probably 1st over, etc.
But do continue to gently scrape the piston crown with something soft. A stick of solder used to be recommended, but that's getting very hard to get these days, at least here in the US. Whatever you use (tool suppliers do sell piston scrapers), don't scratch the metal, but get as much carbon off as you can. Often the stamping stays invisible until you get down to the bare alloy.
And do blow the loose carbon out of the gap between the piston and the bore, if you don't pull the barrels off loose carbon can cause a ring to stick (guess how I know?)

Ken
 
mcnicol said:
Clem beat me to it

Steve, pick up a cheapo Chinese set of internal micrometers and a medium quality set of digital calipers. Measure the bore in several places, but you're most interested in the measurement as low down in the bore as you can get, and the measurement taken parallel to the crankshaft should be the closest to the original. You piston will obviously be slightly smaller than the bore dimension, but if the bore is less than 80.4 mm, it's probably standard, less than 80.8, probably 1st over, etc.
But do continue to gently scrape the piston crown with something soft. A stick of solder used to be recommended, but that's getting very hard to get these days, at least here in the US. Whatever you use (tool suppliers do sell piston scrapers), don't scratch the metal, but get as much carbon off as you can. Often the stamping stays invisible until you get down to the bare alloy.
And do blow the loose carbon out of the gap between the piston and the bore, if you don't pull the barrels off loose carbon can cause a ring to stick (guess how I know?)

Ken
Click to expand...


Why would you measure the worn part of the bore to find out if it's standard or oversize I would measure the top of the bore just above where the rings sit at tdc to find out what the bore size was originally

                                                                                          Dave
 
80mm = standard
oversize 80.4 or 80.8
Click to expand...

Hi, Clem.
Are you out of form?
Original Mondials were available in standard and 2 oversizes (80.4 and 80.6).
There is a 3rd oversize (80.8 ) available, but only from aftermarket
pistons like e.g. Asso.

Ernesto ;)
 
Decoked pistons with a piece of flattened copper pipe, finishing with a suede brush (brass bristles). Still can't see anything stamped, but I'll keep looking.

All valves except one have failed leak test. Will have to grind-in the valves, a job I haven't done for many years.

Cheers

Steve in UK
 
....... the continuing saga.

Haven't removed barrel yet, still working on head. Both exhaust valve guides are worn out. Valves look ok. Thinking of getting all valve guides replaced and seats recut by a local vintage engine specilalist.

Two questions:

-- I can make an extractor for RH camshaft. How do I remove LH camshaft without knocking it out?
-- How do I install inlet valve oil seals?

Cheers

Steve in UK
 
Hi, Steve.

If you use a heat gun to warm up the area around the bearing seats, you can knock it out gently.
You can install the oil seals with a matching socket on an extension. Or use a matching tube.

hth
Ernesto
 
macavity99 said:
Two questions:

-- I can make an extractor for RH camshaft. How do I remove LH camshaft without knocking it out?
-- How do I install inlet valve oil seals?
Click to expand...

No other option... heat the head gently first, the interference fit turns into a sliding fit.

Either fit suitable guides if the early type are still fitted or have the guides machined in situ for the seals.  They are also simply "knocked on".

piet
 
Hey Clem,

What Phil tried to say is that it is not possible to let the chain run beside the crank sprocket on a 750. The 750 is fool proof in that respect.

Marnix
 
agree with Ernesto, 80.4 and 80.6 is oversize available from factory.I am getting old.

Thanks Marnix,you guessed, I was crossing between twins and triples, well I mean it is nearly all flaming triples we gas on about here isnt it? and if the cylinder heads (for triples) were as good as the twins, we would have very little to say at all.PLus your own  (Marnix VDC) English is better than mine, and I live here!

CLEM
 
Ok, got the cams out -- thanks for the advise.

Cleaned and inspected the valve guides and what do I find -- looks like they've already been k-line at some point in the past. Can the old liners be removed and replaced with new?

Cheers, Steve in UK
 
Cylinder head is at the shop awaiting quotation.

Next problem -- barrel is worn out but pistons appear to be good. I've read somewhere on here that Wolfgang can supply liners, new or used. Used cylinder sleeves -- how does that work?

Cheers

Steve in UK
 
Steve,

If the liners are worn, the pistons are too, even if they still look good and measure up reasonably well.  The major problem is the top ring groove, this wears a lot more than the others.  Excessive ring clearance in the groove will turn the engine into a giant oil pump at higher revs.

The pistons can be reclaimed by machining the groove and fitting a wider ring, but the overall cost is much the same as a simple re-bore with new pistons.  (The new liners need to be bored also!)  Using old pistons also means needing to put up with unnecessary piston slap, as the pistons rarely have their "new" shape.  The alloy shrinks, the shape of the piston changes and it will/can no longer perform as intended as the bore size cannot be reduced safely in order to reduce piston/bore clearance.

ASSO forged pistons currently available at OCT, as are liners.  For terminally worn liners, >80.6mm, 80.8 and 82mm pistons are available!

piet
 
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