Reunited with an old friend. (1992 851 content)

griff851

If the heads are getting machine, pull everything out. Swarf gets everywhere.
I see where your going with this, but from the post you have missed measurements, valves to piston. From previously playing I’ve learnt, measure everything (including rod vertical play, the volume of the combustion chamber and head of the piston), know gasket sizes and crush, then work out how much material is going to be removed. If you have all the numbers, then you won’t end up in hell. Think about what comp ratio your after. 13:1 sounds wicked, but your starter motor is going to take a kicking, and you’ve moved into the realm of only using 98 fuel. Not every country petrol station has 98 etc.

Balancing. Measure piston assembly weight before and after to see if it needs balancing, there numbers floating around telling you after what weight change balancing is recommended. Remember is about moving the inherent vibration to a place your not going to sit in for the majority of the time your riding, not removing the vibration.

I’ve read an article or 2 on flywheel mass, in the grand scheme of things as far as power is concerned, it’s about the last thing to worry about because the gains are so small. It’s an energy storage device, what you take out, has to be gained somewhere else. However harmonic dampening is part of its job.

Sorry to bring this bit up after you pulled the valves, but assembly/ disassembly/ assembly is part of the gig. Doing cases you might jag it at 2-3 pull aparts, you might score 12 pull aparts. It’s about getting it right, not she’ll be right. The consequences can be rather expensive. And it’s a piss off if after 5000km gear selection in 4th/5th starts to become an issue, if you know what I mean.
People bleat about how much it cost to get an engine rebuilt. Example because i’m doing bevels at the moment, 60-70 hrs is what it takes if it goes well and your on your game. More for a round case. Note not quoted in dollar terms, then guys complain, but you said X$’s.

brad black

i'd get the 1.5mm groove valves machined to take the 1.7mm collets.

you can get the 1.5mm collets in steel as 66910011B. the 1.7mm collets are 66910011E.

PTwo

griff851 wroteIf the heads are getting machine, pull everything out. Swarf gets everywhere. I see where your going with this, but from the post you have missed measurements, valves to piston. From previously playing I’ve learnt, measure everything (including rod vertical play, the volume of the combustion chamber and head of the piston), know gasket sizes and crush, then work out how much material is going to be removed. If you have all the numbers, then you won’t end up in hell. Think about what comp ratio your after. 13:1 sounds wicked, but your starter motor is going to take a kicking, and you’ve moved into the realm of only using 98 fuel. Not every country petrol station has 98 etc...

Thanks Griff, great points. What about the valve seals and swarf? It seems that they are the last thing you want to be contaminated with metal shavings, but they are pressed in. Is there any way to seal/cover/protect them, or do they need to come out?

Maybe 13:1 is a bit much. What is thought to be the best for a street bike that'll have to run on normal pump gas from time to time?

I'm measuring the head and combustion chamber currently. I'm planning on my squish being around 0.85 (from 1.4), so my compression will increase (around 0.8) from that, but decrease from the material I remove from the piston to obtain the proper squish all around. Obviously I'll measure the dome volume again after machining before making decisions on the head.

Cheers,
Peter

PTwo

brad black wroteyou could take that edge off pretty easily in a lathe.

Here are the results of the piston dome edge being removed and the heads after CC work and 1mm taken off of the surface. This work puts my compression at about 11.7:1, which I'm happy about. I'm hoping this allows for normal gas instead of high octane.

Valves lapped and reassembly has begun.

I found the closer rocker springs to be very easy to assemble using a common garden tool used for removing dandelions. I don't use the notch, just the side, but they have a bend and are a perfect width at the end for getting the springs on. Takes but a second to snap it over the post in the head.

Peter

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