Re-ring or re- bore

Z

Zakredridge

Junior member
Location
United Kingdom
Considering putting new rings in the 1200, Wolfgang says he has some which are made to last 40,000 miles, they bed easily and give good performance with a modern oil control ring.
I don't know whether to re- bore while it's down, it's only done 24,000 miles, but the bores aren't perfect. I don't know if it came from a good home. I don't think it did.
On the re-bore side which pistons, std or Ross high compression?
I'm just wondering if the low compression is the best option, fuel and tractibility wise?
 
Be careful with this, do a bit of research, a chat to Ged Shorten might be in order, he will tell you what route to take. I'm saying this because there are still freshly rebuilt bikes burning oil like there's no tomorrow and they are ending up in his workshop..
 
A big yes to getting the bores measured for trueness and having an experienced engine builder evaluate the cylinder wear to decide if reboring is needed. Wolfgang recommends Ross Racing forged pistons which I used on my 750.
 
Been there before.

24,000 miles: The original pistons will be more than 1/2 worn out.

WAY cheaper to do the job right first time.

Sure, new rings will give you more miles with worn pistons and bores...

Are you a fiscally challenged student? I was at the time and remained fiscally challenged for a while after!

Measure up the bores and buy pistons c/w rings etc. from reputable dealers, such as Wolfgang. Dealer and piston maker will give clearance guidance for the re-boring engineer.
 
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Thanks for the information, the bores aren't showing any grooves or anything that jumps out, obviously need to measure , and if half worn out as stated It would probably be advised to re- bore.
Omega , unfortunately will not supply to private individuals.
There wasn't any oil usage previously to this strip down, or at least not needing top ups between oil changes.
Ideally I want tractibility, and smooth glitch free acceleration, without preferably, additives to the fuel, because of compression or fuel availability.
The price difference between NOS pistons and Ross is not that great, but compression levels.are .
 
Ross HC slugs will give you a nice boost in power all-round. Shouldn't create problems with fuel, but best fitted in conjunction with a good ignition system for a nice gradual advance curve.
 
Zakredridge said:
Thanks for the information, the bores aren't showing any grooves or anything that jumps out, obviously need to measure , and if half worn out as stated It would probably be advised to re- bore.
Omega , unfortunately will not supply to private individuals.
There wasn't any oil usage previously to this strip down, or at least not needing top ups between oil changes.
Ideally I want tractibility, and smooth glitch free acceleration, without preferably, additives to the fuel, because of compression or fuel availability.
The price difference between NOS pistons and Ross is not that great, but compression levels.are .
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I did manage to get some rings from Omega.
They were very nice and helpful.
Paul
 
martymoose said:
What are you people talking about!!! 2 X RGS both in excess of 200,000km, 3C 200,000 plus km before tear down, 120 Jota currently at 115,000km on original pistons and bores, SF2 did 100,000km in my ownership. Unknown km before that in the US. Just ride the bloody thing!
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Well I'm glad you said that because if my pistons were half worn at 24k they must be hanging by a thread at 64 !
 
martymoose said:
What are you people talking about!!! 2 X RGS both in excess of 200,000km, 3C 200,000 plus km before tear down, 120 Jota currently at 115,000km on original pistons and bores, SF2 did 100,000km in my ownership. Unknown km before that in the US. Just ride the bloody thing!
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Yes.
My good old SF2 has around 170 000 on original bores and pistons.
More ride reports, less soul searching.
Paul
 
Agree with Marty.
My SF2 clocked up 200k kays and the Motodd has done 110k kays and the motor now has over 200k though it was rebuilt at 95k.
Maybe it's an Australian thing as we cover huge miles from A to B.
 
My RGS has 135 km on the clock with the original pistons and running fine, almost no oil consumption and the power is fine for country roads where I do not go faster than 150 ks😄👍
 
My SF1 bores were totally shot at 120,000km (, top rings in many pieces, huge ridge, straight to 0.6mm rebore), but that was due to me cleverly running zero air filtration for about 70,000 of that - which included thousands of km on bulldusty Australian outback roads. That's why you'll never see one of my bikes with open stacks on the road. I did run the FCRs on the SFQ with open stacks for a few weeks until I could set up a satisfactory free-breathing filtration system. Cost me all of 3hp at the rear wheel - still leaves more than enough.
 
Marty's on the money. Get the bores measured for taper and ovality, piston to bore clearances, and ring groove widths, that will tell you what you need or don't. Don't get too hung up on wider-than-spec ring gaps either. If it was running fine before and not burning oil, run a ball hone through the bores very lightly, whack it back together and enjoy. 24k miles is just run in as long as it was reasonably treated.
 
breganzane said:
Marty's on the money. Get the bores measured for taper and ovality, piston to bore clearances, and ring groove widths, that will tell you what you need or don't. Don't get too hung up on wider-than-spec ring gaps either. If it was running fine before and not burning oil, run a ball hone through the bores very lightly, whack it back together and enjoy. 24k miles is just run in as long as it was reasonably treated.
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No and yes...;)

A gently-run engine may hold up fine for many more 1000s km, but if regular hooning or extended high-speed runs are on the cards, excessive ring clearance in the grooves can bite rather quickly. The rings tend to flutter at high rpm and break up into 10-15mm long pieces, low compression and excessive crankcase pressure/external oiling resulting. This phenomenon isn't exclusive to Laverda, I've found it in all varieties of 4-strokes, but especially in high-revving multis.

Such a low mileage engine shouldn't show much wear and tear, the worst possibly resulting from standing idle for far too long.

My 3C was ripe for a re-bore at around 60000km, it hadn't led an easy life. The replacement pistons were removed after around 50000km and already showed excessive ring/groove clearance. Dyno runs exposed that the engine was rather tired by then. Again, the engine was pushed hard for most of that mileage. Now on 78mm pistons, the engine runs very strong, but the head does emit some clatter and will require some TLC in the near future. While shim sizes are still well in the ballpark, guides are definitely shot, after around 90000km since re-build.

While it still runs fine with the odo at a bit over 100000km, my RGS now burns around 0.5l oil over 1000km. Pretty sure it's lost a fair bit of its original grunt as well, it doesn't compare very favourably to other RGSs of my mates. But there's a re-worked CR head with a set of 10:1 Assos on the shelf, should get it flying again.

The GTL otoh, shows no signs of slowing down. Last time I looked, the pistons, rings and bores were in perfect shape! Now close to 70000km after fitting, with no measurable consumption between oil changes.

piet
 
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