1982 CB750F...Better Devil

Jimbonaut

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irk miller said:
Just curious, but did you check the true on that countertop? Curious how close it is to a proper surface plate. Most surface plates are several inches thick to accommodate flex from the surface it sits on, as well as being ground to within .0000025"
I'm curious now too - I had to take a punt on it being true as it's the only thing in my world that's even close.
 

Jimbonaut

Well-Known Member
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Here's what I got -



The ruler is the straightest edged thing I've got, but I'm not 100% convinced it's perfectly straight-edged. I can see daylight between the ruler and the granite, but barely. Maybe 0.1mm?
 

Nybz

Member
I found out the hard way on my goldwing, when I attempted to straighten the head a back and forth motion was not the way to do it, but instead a circular motion. Otherwise there is too much pressure on one side doing it back and forth.
I had to take it to a machinist to flatten it back out.

Good luck!


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CarbsAndCylinders

Careful With That Axe Eugene
a sheet of glass is supposed to be flat, can you try that, also flip your straight edge over and see if you get the same results.
 

irk miller

You've been mostly-dead all day.
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CrabsAndCylinders said:
a sheet of glass is supposed to be flat, can you try that, also flip your straight edge over and see if you get the same results.
Technically, float glass is the truest surface of glass, but it's not. It's way more true than his counter, but not as true as a surface plate. I've used thick panes of it for similar purposes in the past, but nothing like the mating surface of a head. All glass is prone to bow and warp, so there is a range of tolerance when it comes to ASTM standard.
 

pidjones

Well-Known Member
A 12" square of 1/4" plate glass with 600 grit spray-glued on worked well on the Hunley head and block. Used Dychem to see the high spots until it showed flat. My surface block was good for seeing if a feeler would fit under. Final testing with Prusian Blue to make sure.
 

wozza

Member
Good old fashioned oil stone oil and figure 8's is how Ive always done it..never had an issue......
 

doc_rot

Oh the usual... I bowl, I drive around...
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You could always have a machinist mill a little off the head to make sure its flat and get a boost in compression at the same time, seems like a no brainer to me :-X
 

Jimbonaut

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Ha! You know what, I’m starting to get pretty comfortable down this rabbit hole. Who the hell knows where it’ll end, but I’m enjoying finding out.

I really appreciate and value the input fellas. Time maybe for a plan b.


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Jimbonaut

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Going to do it proper. Went to my man's shop who has ½" thick plate glass just for this job. Tried removing the exhaust studs that are getting in the way - 2 came out no problem but the others didn't budge, even with a heat gun. Had to down tools but will get more heat on it tomorrow, double-nut the stud and see if I can get those little buggers out.
 

V10Pilot

Member
Jimbonaut said:
Drained some of the oil, wasn't milky or weird smelling and tried setting setting it on fire but didn't light so pretty sure there's no gas in there. Rebuilt the carbs, jammed them back in the bike and hooked up Rhonda's tank as a stand-in. Don't mind the enormous fairing up front, slung that on for shits and giggles...

https://youtu.be/-EHuxVzExoc

Getting a non-runner to start for the first time is a feeling like no other. Love it. Took a while to fire, but that's because (I think) of the empty float bowls and vacuum petcock set-up. You may be able to see the can sitting on the frame - that's Honda carb/combustion chamber cleaner and it's good stuff. Much thicker than regular carb cleaner which - for whatever reason - works really well (guess it sticks around longer, burns slower?). Either way, with the airbox not connected to the carbs and a good 5-10 seconds of that stuff sprayed into the carb body and it's off to the races.

The bike sounds pretty damn good too, no weird rattles, clanks or leaks yet. Did see that one of the spark plug threads is cross-threaded so I guess I'm going to have to pull the head and re-tap it or get a TimeSert in there . Other than that, so far, so good. Will check compression tomorrow, but all four pipes were nice and hot (ie totally burnt myself on all of them) - including the cylinder with the cross-threaded spark plug.

Included in the vid is a close up of the air filter housing. Me and my wife have a jewelry business - if I find a skull in amongst the rats nest in there I'm casting it in bronze and it's going on this bike.

Sweet. So now that I know it runs I'm gonna do the basics on her to the point where she'll pass her safety inspection, then bring her home and get the grinders out. Good people - onwards 8)
That front fairing looks like it belongs on a golf cart!

A running engine is a great feeling. The value just went up 300%.


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Jimbonaut

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Damn, that was a while ago - bike's in a million pieces all over my garage now! Forgotten how the engine sounds it's been so long - man I'm looking forward to hearing it again.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Working on re-doing the mating surfaces (turns out I was wrong about the other day being mating surfaces day. Wasn't even close). Took the head and cylinder block to my friend's shop and spent at least two hours honing them on his glass surface. Now I have a much better understanding of the amount of work involved, and of course the importance of the true nature of the honing surface. They look waaay better now - I'll post up some photos tomorrow.

Tried "breaking the glaze" in the cylinders too. The lines that the tool created in the cylinders however are all concentric (like a thousand tiny rings all stacked eon top of each other). I thought however the rings were supposed to be cross-hatched but I don't see how to make that happen with the drill spinning like it is. How important is it to get that cross hatched hone in the cylinder? I know (I think) it is to aid to movement of oil on the cylinder wall.
 

Maritime

Well-Known Member
I think to get cross hatch you need to move the hone up and down in the cylinder quickly. Don't spin it in place.
 

Jimbonaut

Well-Known Member
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Thanks for the video - that's pretty much exactly what we did but didn't get the cross-hatching. Drill spinning too quickly?
 

adventurco

Nick Ol' Eye
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Jimbonaut said:
Thanks for the video - that's pretty much exactly what we did but didn't get the cross-hatching. Drill spinning too quickly?
Possibly. I brought the XL350's top end to a machine shop and he honed it while I waited. The hone machine was going slow, probably less than 500 rpm.
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
Yeah, I think that's it. Need to dial down the drill. Even with the fine grit stones I'm guessing the honing tool removes material from the inside of the sleeve, and so overdoing it is a no-no?
 

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