E: Engine Damaged quill

[davidd]

That is quite informative.

If the engine is not fully broken in I would not be surprised with those numbers. I would suggest this is why the clearances need to be higher for the Comet than for the Yamaha. Most pistons will be supplied with the clearance recommendations for the Yamaha, not the Vincent.

David

 

[passenger0_0]

All very interesting and both Ed and David make good points.

Please note that the Yamaha is OHC so has a significant amount of oil cooling going on which drags heat away from the cylinder head into the sump. The dribble of oil through the Vincent head to lubricate the rockers and cams takes away very little heat as the volume flow rate is so low.

Another point to note is that the Vincent combustion chamber design exposes a lot of surface area during combustion so looses a lot of heat compared to modern designs.

I like what you've done with the IR camera. Any chance of you or someone else taking an image of a known healthy Comet cylinder and head after a run and recording the ambient temperature?

 

[greg brillus]

I checked with a digital heat gun the temp on my twin's cases where the mating number is stamped, this after a good run on a hot day and it showed over 130 degrees Celsius.

 

[oexing]

Be careful with infrared readings, you´d have to adjust the instrument to specific metals, especially when you aim at polished faces. You would get very wrong readings . Better to put some black adhesive on or a spot of black paint that is easily wiped off after.

Vic

 

[passenger0_0]

Quite right Vic. Different surface emissivity needs to be accounted for.
More importantly though, aside from the exhaust pipe, the cylinder head is the hottest part so we probably need the front cylinder head of either a single or twin rather than a crankcase to be able to compare everiman's initial results.
Any takers?
I wouldn't say 175 degrees C was too hot for an air-cooled cylinder head but a simple comparison will soon sort this out.

 

[vibrac]

Another point to consider is that a new motor runs hotter for a while the pipes on my comet went slightly blue and the tank smoked after my first short run after a rebuild.(and yes I did prime with oil and run up with plug out on my rollers first)
Now I have only done 100 miles and all is a lot cooler
before my first long run I will change the oil my guess a lot of that heat is the piston getting to know the bore

 

[greg brillus]

What those images show is the Yamaha engine is able to turn the heat energy of the fuel into more work, verses the Comet where the top end is absorbing more heat with less output. That is, that the Yamaha engine is more efficient.

 

[everiman]

Thanks for all the input! To answer your questions, Timetraveler, I suppose I could remove the brake plate, but then I would have no brakes! Are you thinking its not getting enough cooling air?
As far as I know, my comet has the original mag and ATD, timing was checked and set with a degree wheel when head was off for the piston replacement, about 4 degrees btd fully retarded. ATD seems OK.
I don't think emmisivity is a factor here, if it was the actual temperature would be even higher, check out the reflection on the fender in front of the exhaust pipe. Dull, as in not shiny, surfaces are fairly consistent, camera was set for .9 emmisivity.
As far as Yamaha vs Comet, same engine size, same fuel (premium), similar consumption, mid to high 40 mpg, Comet bore/stroke 84/90 Yam, 87/84, more or less similar performance, Yamaha revs quicker (smaller flywheel) and is geared lower, top speed might be higher than 110 Kph, but I'll never find out, its pretty scary loose at that speed, Comet will probably do about 80, I have had it up to over 70 before it seized. AFAIC they are as closely matched in output and efficiency as any engines from different manufacturers and design could be.
I will take the advice of those who say wait and see, the comet only has about 25 miles on the new piston, I will check it again after I have a hundred or so miles more on the piston.

 

[vibrac]

But the oil circulation quantity and speed as has been said before is the key the vincent has no major plain bearings and runs on a dribble of oil while the Yammaha would not last a mile on that quantity before it siezed one of its plain bearings (bet it would be the one in the head). Conversely a Yammaha pump would blow every oil line on a vincent in 100 yards (they are and only need to be pushed on rubber hoses) The Yammaha pumps a vast quantity of oil at high pressure around the engine and in doing so removes a lot of heat - just compare the fin area of the two machines to see what looses heat on a Vincent.

 

[Bill Thomas]

Thanks for all the input! To answer your questions, Timetraveler, I suppose I could remove the brake plate, but then I would have no brakes! Are you thinking its not getting enough cooling air?
As far as I know, my comet has the original mag and ATD, timing was checked and set with a degree wheel when head was off for the piston replacement, about 4 degrees btd fully retarded. ATD seems OK.
I don't think emmisivity is a factor here, if it was the actual temperature would be even higher, check out the reflection on the fender in front of the exhaust pipe. Dull, as in not shiny, surfaces are fairly consistent, camera was set for .9 emmisivity.
As far as Yamaha vs Comet, same engine size, same fuel (premium), similar consumption, mid to high 40 mpg, Comet bore/stroke 84/90 Yam, 87/84, more or less similar performance, Yamaha revs quicker (smaller flywheel) and is geared lower, top speed might be higher than 110 Kph, but I'll never find out, its pretty scary loose at that speed, Comet will probably do about 80, I have had it up to over 70 before it seized. AFAIC they are as closely matched in output and efficiency as any engines from different manufacturers and design could be.
I will take the advice of those who say wait and see, the comet only has about 25 miles on the new piston, I will check it again after I have a hundred or so miles more on the piston.

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.