Unleaded fuel

Pulled the RGS cam cover the other day...

My thinnest feeler guage is 0.03mm (a tiny bit more than 0.001"), couldn't get it under 2 lobes, followers were still free to turn, though.  Other valves all around 0.10-0.15mm too tight.  About 7000km since last check, all without additives on straight 95 octane unleaded.

2 long, quick runs; home>Breganze and back, 1 blast through the alps.  Granted, a bit hard on the bike, but I didn't expect THAT much recession!!  

On the other hand, 3C pulled down for crank and piston transplant, valves checked out perfect!  Shims in the 2.60-2.90mm range after 60000km on unleaded BUT with hardened valve seats.

Already got a CR head on the workbench for the RGS, decent valve seats going in shortly. :D

piet
 
My 30Mm includes a few laps of Spa mostly flat out, quite a few of Mallory flat out and lots at Cadwell flat out (though I suppose none of these actually add up to that many miles!) plus a trip over the Alps last year including some long blasts on the autobahn on the way there and back...

--
Dick
 
My 1980 mirage has only needed minor adjustments to valve seats until a couple of weeks ago when i had to do one hundred mile runs six times and keeping it to just under a ton for @ one and half hours.When i did a measure i had 0.127 mm  (5 thou) gaps on exhaust valves inlets ok 0.2mm.I am now down to a brow sweating 1.06 shim on the centre cylinder. Left cylinder 1.85 shim right cylinder 1.95 shim.Taking plug readings always revealed a tan to brown colour now i'm getting a scary grey, looks lean main jets have always been 138.I would like to try 145 maybe that would bring combustion temperatures down  its never pinked and pulls like a train maybe this latest unleaded you cant go by plug colour anymore ?.I agree that a long fast speeds has put payed to my valve clearances just using unleaded and no additive now it looks like head off.Has anyone just renewed exhaust valves and left the seats ? my mirage has the skull head a11 cams.
                                      cheers
                                      adrian
 
Adrian,

Sorry, but your head is done for.  1.06, really...... :o

That would add up to around 1.5mm recession in an area where 1/10s of a mm make a difference, be careful the valve don't pop out the top!!  Not only is the flow at the valve head severely impeded, the compression can't get much lower either.  Danger of valve failure with all its collateral damage is very real.

Sure, you can just fit new (shorter) valves.  But, technically, it's a waste of time and effort, not to mention the cash involved.  Flow will still be buggered and comp will also stay low.  The seats will need a skim, which would recess the valve even further.  And, I'd bet that the guides are just as shot.

Slaughter the piggy bank, have new guides and seats fitted, along with new valves and the engine will be as fresh as it was when it rolled off the production line (provided the remainder is in good nick... usually isn't though)

piet
 
So basically you are all confirming his research findings ie Air/Fuel ratio is the biggest single determinant of valve seat recession and occurs at the highest rate at the highest speeds where the engine is the hottest and the fuel burn the leanest.

Quote:- "Comment: the closer the AFR comes to stoichiometric, the higher will be the recession rate; at or even over stoich the increase is often dramatically due to hotter combustion, higher ex-gas temperature AND, if over stoich, the presence of free oxygen."
 
A steady 100mph on any big Laverda will not necessitate 3/4 or more throttle. My understanding has always been that with Dell type carbs the main jet affects nothing under this amount of throttle. I have seen enough Dell equipped bikes with the mains fallen out to bear this out (blocked or restricted mains being obviously an exception). Has anyone with an 02 sensor as recently discussed found otherwise? The seat recession may be caused by the heat from sustained higher revs (isn?t 100mph just under 6000rpm on a triple, not exactly excessive?)
 
Maybe i should have kept it singing at over a ton to bring in main jets thus cooling valves down !.Any thoughts on grey  plug colour?. If i get the head done should i fit larger valves at the same time ? and rough cost ?
              adrian
 
I've read opinions from various sources that plug colour on unleaded fuel is an unreliable indicator of mixture. I've certainly not been able to draw any sensible conclusions from looking at plugs since leaded fuel has disappeared.

Actually, the only interesting observation I made recently is when I pulled the plugs from my car, which runs on LPG. The plugs looked like new - clean and shiny! LPG must be clean burning stuff. I wonder if I can convert the Laverda to LPG ...

Cheers,
Cam

 
I pulled the plugs on the Pantah a while back and there usually pretty sootly,gobsmacked,they were the classic honey colour,thats using 98,no idea why
 
Cam, I used to have an old IHC 1-ton flatbed I used as a wood truck that ran on LPG. Came from an Idaho potato farm, was equipped that way from the factory. The plugs always looked new and the oil never got discolored. Great old beast, can't remember now why i got rid of it!
Richard
 
I always used leaded 4* fuel from Bayford Thrust at ?1.66 a litre then last year I had to romve the Jota's head so had the cylinder head shop do the seats. All is good.

If anybody also has to remove the heads from their bike I would also recomend Helicoiling the stud threads in the head as well while its off.
 
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