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Discussing seizures on an Iron barrelled scoot today, after the neverending debate (mass debate.. yes.. heard that one..) someone pipped up *cough* about how come they never seized in the 70's but do in the 90's and what was the difference... Only thing? lack of lead in fuel.

Cant find sod all on the tinterweb to back this up as being a deciding factor in why there were less seizures when running in back then compared to today on an Iron Barrelled 2 stroke, but thought i'd ask the learned members of RS their view?

Would the lead have made a difference, should an additive to replace that lead be used? Would it make a positive difference to running an Iron barrel in? (this is all mixture aside. Been there done that argument about percentages of oil in fuel.. There's always the debate that the difference comes from keeping up with faster traffic, more traffic lights, etc, but that just open up a whole different kettle of fish)

..... are you sure they didn't seize in the 70s?


..... though if they didn't seize so much, maybe it's because of the amount of oil they used to throw in there .... remember the great blue clouds behind any 70s stink-wheel ... they seemed to clean up a bit in later years - maybe less lubrication is the reason??

Always been a 4-stroke chap myself.

According to many of the older guys who we were talking with, yeah they didnt seize as often during running in. Could well be the oil mixes were a bit more primative and not as 'measured' as they are now... they reckoned the mixes hadnt changed, maybe it was just their memories of it though.

Funny but I remember my old RD's seizing fairly regularly back in the late 70's (usually when closing from full throttle rather than running in).

More likely that in the 70's people were more mechanically minded and less likely to run them without any 2 stroke in.

Could also be some of the modern synthetic oils people are using, or manufacturers are jetting them tighter for emission regs?


Pretty sure lead would make no difference though, as I'm running my old TZR on unleaded with no problems.

Hmm could be the oil choice I suppose, but a lot of the modern oils claim superior performance and the like. Clearly that should be taken with a pinch of salt or six, but it could be theyre running in on synth rather than a mineral oil mixed in with the fuel. The scoots in question are lambrettas running larger bore iron barrels, it's not the manufacture, theyre on par or above the old italian barrels, thats known and jetting tends to be a bit on the rich side by all accounts. No real change from the ones of yesteryear as far as the barrels and jetting go. It'd be interesting to see if the fuel has made a difference though.
As an aside, how do you run in your TZR when it gets a refresh? My MZ got a very basic run in cycle on a dyno then thrashed to within an inch of it's life, which did it no harm and im wary of the claims they have to run these scoots at '40 mph' for god knows how many miles on a rich mix. Im going to rebuild the 200 vespa soon and really cant see a reason to religiously stick to 'X' mph for 'X' Miles. Ride it like you stole it as long as it gets warmed up properly makes more sense to me....?

I had a set of KH triples, and those buggers siezed the middle pot often if you relied on the standard oil pump system!

BUT - I do seem to remember that most of us were generous with our 2 stroke oil - ie, added directly to petrol tank, and that stopped it - well - reduced it at any rate!

I agree with that, we never skimped on the oil.




Come to think of it, it's a habit that dies hard, even when you are getting a faceful of exhaust from a chainsaw or hedgetrimmer.

I think that positive lubrication systems cleaned up the two-strokes act no end, but I wonder if it also made them more prone to seizure. I had an RD350YPVS-based special some years ago and that had an unpleasant appetite for seizing, but I think that was down to a carb/jetting problem that I never got to the bottom of. Running it on pre-mix rather than oil pump reduced the incidence but didn't stop it entirely.

But lead certainly is a lubricant, that's one of the reasons valve seats liked it so much...

I also think one of the reasons the older bikes were a tad more reliable (although I didn't know the 90@s bikes were prone to nipping up) was down to engineering techniques used in the machining of the barrels.

Honing techniques have changed considerably over the last 30yrs to a level where the amount of honing now done is to get a barrel to size and to prepare the surface is almost negligible, where as in the 70's honing was a requirement needed to get the barrel to a decent level of finish & size.

I've heard a number of people commenting that there is nowhere for the oil to sit these days, the modern barrel surface is super smooth and with the close tolerances run in today's water cooled 2 strokes coupled with very efficient piston rings used well....................maybe this is partly the answer??

Only a thought as I sit here remembering the numerous seizures on KH triples, Suzuki GT's and loads on my Yamaha RD400 beckett tuned proddie bike back in the good old days

F9

That would make some kind of sense F9.

i remember when back in the 70's and you either got a new cylinder or had an old one renovated, we always jumped up the oil mixture in the gasoline with a couple of %...never had a problem. but i guess this is somewhat different than on todays 2 stroke with separate oil tanks. just me 2 eurocent

Finn

Agreed with falco9

Tolerances with aircooled were, shall we say, agricultural. Watercooled allowed for a tighter tolerance giving more power etc blah blah....Downside was they needed more countermeasures to keep them on the road. Which the majority of us old farts took on board .

I also had a kh250s1. Usual middle pot syndrome. I remember blasting down the M56 before it got shite. When I looked back all i could see was smoke.

Them were the days

I'm sure a lot of riders here will remember what we used to refer to as "The Shaking Hand" syndrome. I'm sure many will have their own description for it

For us this was our "local" term for the involuntary shaking of the left hand at the end of a decent high speed 2 stroke run. Caused by the leaving your hand "hovering" over the clutch lever for minutes on end in case it "nipped up" and you needed to whip the clutch in sharpish.

Mine used to shake like a feather in the breeze and used to make me coffee froth when we stopped at the next cafe maybe I should have sued Yamaha for "Vibrating White Hand" syndrome

Happy days eh?

F9

Having at least 2 fingers permanently hovering over the clutch lever does rather shout out 'ex stinkwheel rider', doesn't it? Personally I think it's a huge shame that the 2T engine has effectively been left to whither on the vine by all manufacturers. It seemed only a short while ago that manufacturers such as Orbital were talking about a brave new era where the two-stroke would be king.

To be honest, I think that chance has now gone and the electric bike will be the Next Big Thing. Can't say I'm waiting with baited breath for it...

Kwackerz wrote: As an aside, how do you run in your TZR when it gets a refresh? My MZ got a very basic run in cycle on a dyno then thrashed to within an inch of it's life, which did it no harm and im wary of the claims they have to run these scoots at '40 mph' for god knows how many miles on a rich mix. Im going to rebuild the 200 vespa soon and really cant see a reason to religiously stick to 'X' mph for 'X' Miles. Ride it like you stole it as long as it gets warmed up properly makes more sense to me....?

I'm not too fussy with it - I do it on a practice day.

1st session rev it to 8k
2nd session rev it to 9k
3rd session rev it to 10k
4th session rev it to 10k and rev it out a few times (revs to about 10.5k)

After lunch just cane it

I dont bother with upping the jetting or anything, or a richer premix - but always cover the clutch