E: Engine Damaged quill

[everiman]

Yamaha 500 singles do not have plain bearings except the small end of the connecting rod, and sliding valve lifters, same as a Vincent, everything else is ball or roller bearings, built up crankshaft, one piece connecting rod, dry sump, Yamaha oil capacity is less than Vincent, 2.4 liter, oil pressure the same or less than the comet, typical for engines with rolling element bearings, recommended lubricant 20W50, the major lubrication difference between Comet and Yamaha is that Yamaha's engine oil also lubricates the transmission and primary drive, so even more opportunity for the oil to get into trouble .

 

[bmetcalf]

Maybe a slightly higher speed would be better ?.
Cheers Bill.

Spoken like a true Vincent man! The likes of Burns, Free, and Matson.

 

[Bill Thomas]

I was only thinking 40 mph Bruce !, I am OLD now !.
Funny , I went out on the ex L/ning yesterday, With the Mk2 amals, Bad traffic and through the Forest for 70 miles, Mostly at 40 mph, It has never been as good, Well pleased, There is so much traffic where I live now, It's a pain. But She still goes like stink when I want it to.
Cheers Bill.

 

[timetraveller]

Yes, I was thinking that the cooling might not be correct. Often an oil leak on a Vincent engine is shown by oil being dragged forwards by the 'vacuum' behind the plate I was discussing. I am very aware that the brakes would be compromised but if you had, or could borrow, a twin cable handle bar lever and make some temporary supports for the cable outers near to where the plate was then you can make a front brake which works well. You have the correct equipment to test the hypothesis that the plate causes trouble but whether you have the time etc to do it is another matter.

 

[Bill Thomas]

What I was thinking at 30 mph, Which is less than 2000 rev's, Maybe it is still retarded, I read somewhere it's fully advanced at 2000, So at 40 mph it's about 2500 revs, Just my thoughts. Cheers Bill.

 

[everiman]

[ I think it's well worth fitting an Hydraulic steering damper, Not standard, But better to be a bit more safe.
You don't have to go at 80 mph to get into trouble.
As for your running in, Maybe a slightly higher speed would be better ?.
Cheers Bill. ]

Ha ha, my personal super power is finding the wiggles wobbles and shakes of a moving motorcycle, Comet handles impeccably. Did a higher speed run this morning touched 70 briefly, same result. I will keep doing short break in runs for a while.... see what happens after I get 100 miles or so on the new piston. I did open up the ring clearance a bit before installing, they were barely .010, I like them wide so now about .020.

 

[Martyn Goodwin]

What I was thinking at 30 mph, Which is less than 2000 rev's, Maybe it is still retarded, I read somewhere it's fully advanced at 2000, So at 40 mph it's about 2500 revs, Just my thoughts. Cheers Bill.

Here are the advance curves with the ORIGINAL lucas ATD. The data is measured at ATD revs, which are HALF engine revs - so to relate it it the motor you need to double the rev number.

So the standard setup advance starts around 1,500 rpm and is not fully advanced till 2,300 rpm. As the ATD springs get weaker (with age??) then full advance happens at a lower RPM.

Martyn

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[kettlrj]

I would have a good look at this motor. There are signs of butchery, judging by the half time pinion nut, chisel mark and dot punching no where near the keyway. The oil feed quill looks like it has picked up in the end of the crank, which seems to have some of the quill stuck in the hole. As for the piston, I always chamfer the bottom of the skirt on the inside. This has the effect of throwing the oil up at the piston crown instead of it being scraped off by the flat bottom surface. It also reduces the pumping losses very slightly.
Best of luck with the investigation.
Regards Richard.

 

[everiman]

So far, about 100 miles on the new piston and cylinder. I have checked and reset the timing again, fiendishly difficult for me to get it right, no matter how many times I set it, it ends up either slightly advanced or slightly retarded after I tighten the ATD and recheck. So this time I went for slightly advanced, probably between 6 and 8 BTDC. Engine still runs very hot, spark plug and exhaust side are in the low 300 F range after a 10 mile run, today it was a faster one, 40 to 60 mph nice cool and damp morning no traffic temperature 16 C. Spark plug is consistently a medium tan color.
It seems every Comet story in MPH I have read so far ends the same way, engine goes bang. See the Vancouver chapter story in MPH 833. How reliable is the Comet anyway?

 

[Bill Thomas]

I think sometimes we ask a bit much from these poor old bikes, I know I do !, I don't think Comets are a bad bike, But things have to be loose !, And a bit rich, To keep them cool. Much of the trouble started when blokes started fitting low clearance pistons, I never have yet.
Also with valve seals and small holes in the rocker feed bolts, ie less oil, Might make the head hotter ?.
You have not told us what Spark Plug you use ?.
As soon as these pistons came out, The word got out, You must give them a bit more clearance.
We have been having some nice weather in UK of late, Hot, I got home on my Twin yesterday, After an 80 mile run, The last bit was a bit brisk !, And sitting in my garage after some time, There was a loud Crack,
I would not mind a Ping, But I thought something bad, Just been out today and it was fine.
I think you worry too much, Like me !. Cheers Bill.