Rebuilding the Jota

Gareth99

Gareth99

Full member
Following an "off" at Cadwell at the end of last season I had to completely strip down the Laverda to make sure there was no crank damage (fortunately there wasn't), and I'll post photos on here of the rebuild.

I took the opportunity to get the engine soda blasted and the casings polished, and the frame powder coated. Due to the time taken to get the engine casings back after a very busy Stafford show, I wasn't able to start reassembly until last week.

Things were going well until I noticed a small crack in the lower of one of the piston rings on the LHS piston and sure enough, just as I touched it, a part flew off and into the engine casing! Grrrr!! luckily I could fish out with a magnet and after much checking that I'd got all the offending parts, I ordered another set of rings.

Next job will be to rebuild the clutch cush drive with new rubbers.
 

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is not actually a Jota by looking at those pistons, those look like Mondial flat top pistons

what you need to work out is why the ring broke in the first place, they don't generally just crack for no reason
grab a set of feeler gauges and measure the side play on your top and middle piston rings in their lands
you are wanting to see less gap then 0.07mm or in that imperial stuff around 0.003", worst ring to land gap I have measured on a Mondial was well over 1mm

if your ring lands are worn then the pistons are junk and you need to replace them, be a great opportunity to get some "Jota" style pistons

 
Yep, go slow pistons. The right hand one has NANNA 75 written on it, so probably built for granny to ride to church on a Sunday.  :LOL:
 
Hi Gareth - If pistons are OK - you can always skim the head to get CR up. have got 75mm ring sets if you need them at sensible money. - Regards - Phil
 
All very wise comments, especially the sharp eyed nail spotter !! Well done!

Redax, I'd checked the ring lands, gaps and fit in the bores and they all looked good, but thanks for the info as I was going by old engineering "feel" rather than hard numbers. As part of the root-cause-analysis I found a crease in the ring compressor that i was using and think that the end of the ring got caught up in it as there's a small tell tale scratch on the coating.

Yes, I realised the pistons weren't the high compression ones I'd expected when I bought the bike, and only found this out when I took the engine apart this year. Strange, as the previous owner had gone to the bother of fitting 4C cams. So I now have the quandary of whether to fit HC pistons or leave the standard flat tops in and make it more rideable? Decisions, decisions..... Anyone got a set of Jota style pistons and rings then? :-)
 
Anyone got a set of Jota style pistons and rings then? :-)
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Cams are easy to fit, pistons less so.

Jota pistons freely available.  Chuck away those cast Mondials and fit some luvverly forged JEs or Omegas.  Almost too blingy to go inside a motor where they won't be seen. :D

If you want to improve the rideability as well as the performance then fit 'Jota' pistons and RGS grind F1 cams, makes for a fine motor.
 
Nought wrong with cast Mondials as long as you're not going racing, or tend to ride constantly at 110% on public roads. :D Forged pistons don't last that much longer, at 60000km they'll be just as knackered as cast items.  Always the ring grooves, if nothing serious happens before that.  I've seen top-quality Assos  past their prime at 30000km, some people manage to fuck everything up.  Piston life depends a lot on common sense and maintenance.

Slightly higher compression doesn't make a triple peaky or unrideable, quite the contrary.  Adds a bit of pep, but still retains the tractor-like characteristics.  Going wild with cams is what makes them unrideable, things like C7 cams sacrifice low-down torque and require completely open, anti-social exhausts. 

piet
 
Reggie3cl said:
If you want to improve the rideability as well as the performance then fit <snip> RGS grind F1 cams, makes for a fine motor.
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At the expense of reliability perchance?... ::) ::)
 
Reggie3cl said:
Uh oh!  :o
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Nicely adjusted ignition timing and carburation, as well regular oil changes, think they like that.... ::)

I'm with Piet, nowt wrong with the Mondials. The ones I have found inside my 3C engine had approx. 110000 km under their belt, manufacturing pattern still visible on the skirts. All dimensions well within specs, except the top ring grooves being waaaay out. Carbon deposits in the exhausts port have been worse than I have ever seen on any of my 2 strokes. :-X

Back then when I restored the 3C, there was a kind offer from OCT for a set of NOS Mondials, combined with set of new cast iron liners, that I couldn't refuse. Never regretted it. With the 4C cams, the engine runs sweet and responsible at low revs, and above 5000 all hell breaks loose. Like it.
 
Reggie3cl said:
If you want to improve the rideability as well as the performance then fit 'Jota' pistons and RGS grind F1 cams and new buckets, makes for a fine motor.
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Fixed
 
The new buckets CAN takes some fiddling to fit as well.
No dramas since mine went in though. Very big THANK YOU to all involved in the fix. I know it was STRESSFUL to all.
 
At the expense of reliability perchance?...
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Nope.  F1 cam has a good profile - it was a more modern design than the A11 or 4C after all.  You don't get the big lunge at 5000 or whatever with F1s as you do with 4Cs, but that's a good thing really.  I didn't change the buckets, but Keith did dial in the cams for me.

The only thing the bike could have done with was some head work, always felt like there was a little more to come at the top end.

F1dyno.jpg



 
Reg, I think he refers to the issue he had with his set of F1 cams.
Seems the cam lobes were hardened harder than the cam buckets, causing serious issues.
 
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