1st Oversize Pistons

J

Jota1981

New member
Hi, Looking to rebore and go first oversize on 1981 Jota barrels. Can anyone suggest what's the best bang for your buck pistons I should be sourcing and where I can get them from ??  Cheers  Steve
 
Yep standard 1981 Jota. Its done 150,000 kms now so looking to go first oversize. Will do a leak down test first though. Cheers
 
you might only need a de-ridge, glaze bust and new rings
clean up and measure, measure and measure again, new rings is always a must on stripping an engine  (IYWMHO) as is new valve lap and springs, that is the absolute minimum, but you can never tell, measure and measure again, a lot depends on what running in the engine had in the first 2000 kilometres or so of its life, oil etc, and if it has ever been apart by unknowns.
CLEM
 
If there are ridges from ring wear it's hard to imagine the bores are still worth leaving - especially at 150,000km!! Pistons are a consumable that have a service life just like most of the moving parts on the bike. Ring lands for the top ring are highly likely well beyond tolerance.
 
Yep agreed. I'm the original owner so know the bikes history well. Its been loved and babied its whole life ... replaced the rings a few times ... new valves and bottom end bearings. As most know these engines come apart very easy once out of the frame and are simple to work on. A real joy after working on my other 2 bikes ... Yam MT01SP and BM R1200GS. So .... back to the original question .... anyone know best source of pistons. ???? Cheers Steve
 
If you're in Brissie (or anywhere in Oz really) it's a no-brainer.  Take (/send) barrel to Red and get him to supply Ross pistons and bore to suit.  If your head is similarly tired get that done too... and while you're at it... the crank... and...  :D
 


Do the Ross piston route with Red.

The Ross Pistons are beautiful. 10 to 10.5:1 depending on your chamber volume and head gasket thickness
you can play with this a bit by altering cylinder base gasket thickness and adjusting the squish.

I am told 78mm is the largest size one can safely fit in the 1000 liner. To do this you must be certain your liners are concentric
else you may have too thin a wall section.

I fitted 77mm in my 3C

I am told these pistons are the same ones used by Piero in his spaceframe. Tom and Gijs also are using them in their race bikes,
one of the Oz-laverda race engines has them also.
No known piston failures with the ross units in the 500s or triple race engines.

Valve reliefs accommodate 40mm inlets and at 248g they are lighter than the stock 75mm pistons (261g)
The Ross piston rings require filing to the correct gap.





 
OK thanks all. I'll get a price from Red after I confirm with leak down test. Gotta say the brake upgrade is tempting. Riding the Jota alongside my other "modern" bikes the brakes are the stand out difference. Modern 6 piston callipers are way superior. Performance wise though the Jota still cuts it .... the engine feels so solid and robust and just loves to be thrashed. Really outstanding for a bike that's nearly 40 years old ! I'll keep the brakes as original as possible and work on grip exercises.  Steve
 
Yeah good point Cam. Hey I lived in Tassie for 5 years. A little place called Lucaston near Huonville. It was there I grew 2 heads and laugh at mainlanders ....  :D  Cheers
 
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