Bad noise after rebuild
- Thread starter Mr-Wolf
- Start date
crazypj
Split personality, I fake being smart
Seats shouldn't need re-cutting, I've never had one damaged when motor came in with bent valves from a bad re-build. (snapped valve is a different story though 
)
It would be a very good idea to get a decent magnifier and check valve guides though as they can crack when valve bends.
There are also other things you can do to keep costs down.
Instead of having seats cut or lappi ng the hell out of them,get some carborundum cloth tape (the red/brown stuff)
Cut a piece large enough to cover vale head, make a hole in it for stem and break any glaze on valve seat.
Don't mess with valve head, the coating stays on there.
After re-build, set valve clearane to 0.004" intake and 0.006" exhaust. test ride at least 25 miles.
Let motor cool down 6~7 hrs and re-set valves to standard clearance (0.002" intake, 0.003" exhaust)
The idea of extra wide valve adjustment, is to peen the valve and seat sealing up the 'pores'.
It's worked for me many many times in the last 35+ yrs 8)
If you can't find 650 valves, check part numbers for 500f and 550f. I think they are the same but maybe smaller head diameter? (it's just too long ago I was doing this stuff)
You can probably getaftermarket one piece stainless for roughly the same cost as stock Honda
I know this sucks, but, I've never had much success re-using Honda 4 head gaskets.
Even if they initially seal, they stat leaking after a few thousand miles. The CB750 is such a PITA I wouldn't even consider re-using gasket. 500/550/650 can be done with motor in frame so you don't have much to loose trying it. Maybe get some aerosol high temp sealer and spray both surfaces? (I use Coppercote with solid copper gaskes, works for me ;D )
)It would be a very good idea to get a decent magnifier and check valve guides though as they can crack when valve bends.
There are also other things you can do to keep costs down.
Instead of having seats cut or lappi ng the hell out of them,get some carborundum cloth tape (the red/brown stuff)
Cut a piece large enough to cover vale head, make a hole in it for stem and break any glaze on valve seat.
Don't mess with valve head, the coating stays on there.
After re-build, set valve clearane to 0.004" intake and 0.006" exhaust. test ride at least 25 miles.
Let motor cool down 6~7 hrs and re-set valves to standard clearance (0.002" intake, 0.003" exhaust)
The idea of extra wide valve adjustment, is to peen the valve and seat sealing up the 'pores'.
It's worked for me many many times in the last 35+ yrs 8)
If you can't find 650 valves, check part numbers for 500f and 550f. I think they are the same but maybe smaller head diameter? (it's just too long ago I was doing this stuff)
You can probably getaftermarket one piece stainless for roughly the same cost as stock Honda
I know this sucks, but, I've never had much success re-using Honda 4 head gaskets.
Even if they initially seal, they stat leaking after a few thousand miles. The CB750 is such a PITA I wouldn't even consider re-using gasket. 500/550/650 can be done with motor in frame so you don't have much to loose trying it. Maybe get some aerosol high temp sealer and spray both surfaces? (I use Coppercote with solid copper gaskes, works for me ;D )
Mr-Wolf
Been Around the Block
So I went and bought a complete head from a scrap yard a couple hours away for $100, guy said it looks good and all the valves Are in good shape. Also ordered a whole new rebuild kit because it was a couple bucks cheaper and will be here in a few days vs. a few weeks for a head gasket from England. Also going to look for a roll pin to replace the broke one on the assembly.
Anyone need a gasket kit? Sans head gasket?
Or a head and exhaust valves (had them check by a machinist they are perfectly straight)? Hit me up I'll give you a deal!
Also selling other stuff on the selling page if anyone is interested. At this point it's a make an offer and pay for shipping lol
Anyone need a gasket kit? Sans head gasket?
Or a head and exhaust valves (had them check by a machinist they are perfectly straight)? Hit me up I'll give you a deal!
Also selling other stuff on the selling page if anyone is interested. At this point it's a make an offer and pay for shipping lol
crazypj
Split personality, I fake being smart
Use a solid pin instead of roll pin.
Not 100% sure but I seem to remember a pin from chain link fits (although can't remember which one : ) It was a lot quicker than waiting for genuine Honda pin and possibly a better fit as it needs to be tight
Use cutting disc on Dremel to shorten it after it's in crank so advance bolts back on properly. (easier to cut when 'held' by something solid)
Not 100% sure but I seem to remember a pin from chain link fits (although can't remember which one :
) It was a lot quicker than waiting for genuine Honda pin and possibly a better fit as it needs to be tightUse cutting disc on Dremel to shorten it after it's in crank so advance bolts back on properly. (easier to cut when 'held' by something solid)
Mr-Wolf
Been Around the Block
crazypj said:Use a solid pin instead of roll pin.
Not 100% sure but I seem to remember a pin from chain link fits (although can't remember which one :
Use cutting disc on Dremel to shorten it after it's in crank so advance bolts back on properly. (easier to cut when 'held' by something solid)
That's a good idea! I'll see what I can find.
So how should I go about cleaning this? Should I soak it in something? I figure if I have it off might as well soak it. Or should I just clean it one piece at a time?
Why yes those are perfectly good boot with no cracks!
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Mr-Wolf
Been Around the Block
Couple real quick questions.
1. The long bolts that hold the cylinders to the lower half, how important is it that they all have washers? Because I only have like 4 so I'm thinking that's why I leak oil, because they are just a tiny bit too long.
2. should I undo the entire thing so I can get to the base gasket and copper coat it?
I will have more after this, like why isn't it charging my battery(I have some things I know to check first), and tuning carbs.
1. The long bolts that hold the cylinders to the lower half, how important is it that they all have washers? Because I only have like 4 so I'm thinking that's why I leak oil, because they are just a tiny bit too long.
2. should I undo the entire thing so I can get to the base gasket and copper coat it?
I will have more after this, like why isn't it charging my battery(I have some things I know to check first), and tuning carbs.
crazypj
Split personality, I fake being smart
You need to strip the head for cleaning, change valve guide seals while your there.
I don't remember 650 having any long bolts? (do you mean the studs?)
Fit thick copper washers under dome head nuts on studs, 5/16" is usually a better fit on 8mm than a metric washer
If bolts should have a washer, fit a washer. It's a good idea to make sure the threaded holes are clean to the bottom, 4.5mm drill bit for 6mm thread) and 6mm for 8mm thread (in your fingers not drill motor) to make sure there isn't any crap preventing bolts going all the way down then a thread chaser.
I don't remember 650 having any long bolts? (do you mean the studs?)
Fit thick copper washers under dome head nuts on studs, 5/16" is usually a better fit on 8mm than a metric washer
If bolts should have a washer, fit a washer. It's a good idea to make sure the threaded holes are clean to the bottom, 4.5mm drill bit for 6mm thread) and 6mm for 8mm thread (in your fingers not drill motor) to make sure there isn't any crap preventing bolts going all the way down then a thread chaser.
