1979 Mirage: wear on splines - crank/primary chain drive sprocket.

P

pumzica

New member
looking for advice please, and living in hope ....
looking for an easy solution though I suspect none is available.

Recently totally rebuilt engine after little end failure under load.  all running beautifully these days and powering along like never before.

two issues now

1/  there is a rattle like a bag of nails at tickover due to play/wear on the splines on splined linkage between the carnk and the primary drive sprocket.  Under load this disappears.  The crank was balanced and reground when out and to hand.  We did not think of this wear at the time.  We have tried a new-ish primary drive sprocket and the rattle is reduced but does not go away as the wear seems to be shared between the two parts.  I was persuaded to use some liquid metal which worked for a short while but then gave out and appeared as a sludge when changing the oil - I wish I never agreed to this.  I can't think of anything else to do except live with the bag of nails - can't afford the cost/time/effort/emotion of new crank and sprocket (if indeed I could find them).  Any ideas welcome!

2/  there is oil seepage from the front stud nearest the camchain - all surfaces were skimmed for the best possible seal, but this persists with or without gasket goo.  Could this be the result of the oil within being pressurised by the movement of the camchain at this point I wonder, and is there an interesting solution perhaps?

All comments welcome, however frank!

Thank you in anticipation



 
First question I would ask is how tight did you torque up the Jesus nut on the end of the crank?
Has to be VERY tight.
Permanent cure would be to strip the engine and replace that segment of the crank, but that's a hell of a lot of work.

Is there wear visible on the splines on the crank?
Could it be built up and filed back?

Are you sure the noise is from the front sprocket?

Are the front and read primary drive sprockets in line? The rear one needs to be shimmed out to match with the front one, which is set. Use a straight edge. I had a noisy primary drive on a triple back in the day and found out the rear sprocket was able to float as the DPO had omitted the shim.
Fit a Duplex primary chain (yes, 2-row) from Iwis as not only do you get a new chain but it runs quieter than the triplex chain.

Oil leak from the front stud where the head is bolted to the barrels can be quite common. Is the head flat? Is the gasket surface totally clean?
Did you use the correct torquing down sequence?

I'm sure there will be some more folk along in a minute with more ideas.
 
New sprocket and some Loctite 660 should fix it, unless it is totally goosed be sure to follow the instructions with the Loctite to the letter, when it says clean it means clean. Curious to hear more about your reground crank....
Check the oil around the front stud is not coming out of one of the exhaust ports or from a crack at the top of the head, oil will run down from there and appear to be leaking out of the front stud.



    Keith
 
One thing I spotted recently was what I had thought was a weep from that spot was actually coming from the cam cover gasket.
The replacement rubber gasket was thinner than standard allowing the 6 allen screws to bottom out before the rubber gasket was compressed enough.
From memory the duff gasket was 1.8mm thick and the correct one was 2.8mm thick. Put the correct one in and leak gone.
 
laverdakeith said:
Curious to hear more about your reground crank....
     Keith
Click to expand...

aye, am very curious to hear more about your reground crank
where did the oversize big end rollers come from ?
how did you make larger cages to hold the oversize rollers ?
etc
 
redax5 said:
laverdakeith said:
Curious to hear more about your reground crank....
     Keith
Click to expand...

aye, am very curious to hear more about your reground crank
where did the oversize big end rollers come from ?
how did you make larger cages to hold the oversize rollers ?
etc
Click to expand...

Me too.... :D

The primary sprocket can be shimmed to take up the play, works quite well, for how long depends on how well it is done!

Jesus nut... tight, tighter, fuckin' tight.  Don't forget the Loctite AND the tab washer, belts and braces for me in this case!  Never seen a stripped thread there!

A lot of noise often comes from the clutch hub, this should be a tight fit on the mainshaft.  Can be partly cured by adding an o-ring to the rear a la 750.  If the clutch drum splines show a lot of wear, that will produce one hell of a clatter as well.  Can be seriously reduced with the Mk II/120? sprung double clutch plate method.  New cush drive rubbers can work wonders too!

pumzica said:
all surfaces were skimmed for the best possible seal, but this persists with or without gasket goo. Could this be the result of the oil within being pressurised by the movement of the camchain at this point I wonder, and is there an interesting solution perhaps?
Click to expand...

Bit quick off the mark, before you really knew what was going on?  Damage done...

I assume oil seepage from the cam chain tunnel at the cylinder/head joint.  Leaked, and you tightened, still leaked and you tightened a bit more... the stud is often over-tightened which causes the gasket to spread and the cylinder casting to distort or even crack in that area, especially on early castings.  Later ones were stiffened up considerably.  The head is a lot stiffer there and rarely causes any issues.

piet
 
redax5 said:
laverdakeith said:
Curious to hear more about your reground crank....
     Keith
Click to expand...

aye, am very curious to hear more about your reground crank
where did the oversize big end rollers come from ?
how did you make larger cages to hold the oversize rollers ?
etc
Click to expand...

Me too - I thought they were a replace only part.......but what do I know (dunno)

As for the drip from the front of the camchain casting - what year is your bike? Around 1976/77 they were all ally and had a habit of cracking. Not really a problem (and can be welded), but if it's only a drip or two - get a rag and keep it in the tailpiece.

Could this be the result of the oil within being pressurised
Click to expand...

Oil pressure...on a Laverda?  (hahaha)  (sorry, couldn't resist that). Laverdas run a very low pressure system and (others please correct me if I am wrong), I don't think there is the slightest chance of oil pressure causing a leak.

Pete
 
Thank you for all suggestions - the bike will be back in the Lab in a few weeks' time and will apply the thoughts provided.

Just to clear a couple of queries up - apologies for typo which has unsurprisingly created interest:  crank was balanced and given new bearings, not re-ground.

Best wishes





looking for advice please, and living in hope ....
looking for an easy solution though I suspect none is available.

Recently totally rebuilt engine after little end failure under load.  all running beautifully these days and powering along like never before.

two issues now

1/  there is a rattle like a bag of nails at tickover due to play/wear on the splines on splined linkage between the carnk and the primary drive sprocket.  Under load this disappears.  The crank was balanced and reground when out and to hand.  We did not think of this wear at the time.  We have tried a new-ish primary drive sprocket and the rattle is reduced but does not go away as the wear seems to be shared between the two parts.  I was persuaded to use some liquid metal which worked for a short while but then gave out and appeared as a sludge when changing the oil - I wish I never agreed to this.  I can't think of anything else to do except live with the bag of nails - can't afford the cost/time/effort/emotion of new crank and sprocket (if indeed I could find them).  Any ideas welcome!

2/  there is oil seepage from the front stud nearest the camchain - all surfaces were skimmed for the best possible seal, but this persists with or without gasket goo.  Could this be the result of the oil within being pressurised by the movement of the camchain at this point I wonder, and is there an interesting solution perhaps?

All comments welcome, however frank!

Thank you in anticipation




[/quote]
 
Loctite 660 aperently works well, but I have used Loctite quick metal (PPN9804012) which might even be the same stuff, as Keith says, it must be clean, clinically clean in fact, so wash everything with petrol at least twice, then wash again useing methylated spirits, then once more useing cellulose thinners, allow everything to dry, dont forget the quick metal needs an activator (Loctite 7649) plus a new tab/lock washer and you will get no where if you dont have a very strong crank locking tool, and a spanner to tighten the jesus nut which needs to be about two foot six long.

If all else fails the sprocket can be welded to the crank, this loses you nothing since the  crank end web is shot, so is the sprocket, (lay the bike on its side, and cover everything except the weld area with a large sheet of leather , such as an old welders apron with hoile cut in it) if and when you have to strip the motor the sprocket can be cut off after you dismantle the whole unit, if you want to, but why bother, just get the crank pressed and chuck the welded bits into the bin.
CLEM
 
there is oil seepage from the front stud nearest the camchain - all surfaces were skimmed for the best possible seal
Click to expand...

  If you've skimmed the top of barrell - the top flange of the liners will need to be skimmed to keep them 4 thou (0.10mm) below top land of barrell otherwise the flame rings on gasket have nowhere to seat and this can cause oil leakage. - Regards - Phil
 
phil37 said:
there is oil seepage from the front stud nearest the camchain - all surfaces were skimmed for the best possible seal
Click to expand...

  If you've skimmed the top of barrell - the top flange of the liners will need to be skimmed to keep them 4 thou (0.10mm) below top land of barrell otherwise the flame rings on gasket have nowhere to seat and this can cause oil leakage. - Regards - Phil
Click to expand...


FUCK!!!  Top of my barrels were skimmed so now flush with the top of the liner. If it does leak I'll have to go back to my original idea of using the copper head gasket I made after being talked out of it by Red.
 
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