1982 CB750F...Better Devil

Fired up the old girl, no leak from the base gasket and no hammering of pistons against the incorrect head gasket. I'll never use jobber parts again for significant parts of an engine rebuild. Honda OEM gaskets and o-rings are obviously more expensive, but a no-brainer in the grand scheme of things. Lesson learnt there.

There's a bit of noise however still, sounds like something labouring, I pulled the valve cover and checked valve clearances - a lot of them are quite a bit looser now that the engine has cycled than they were when I rebuilt the engine. I'll try and get a vid uploaded. Can valve clearances create engine noise? I'll also check the three starter clutch bolts to see if they've loosened. I know I tightened them during the rebuild but anything's possible.
 
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These are the valve clearances (in inches) before running (idling) the engine (worth mentioning again that I switched out the 750 cams for 900 cams) -

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and these are the measurements I took yesterday -

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The clearances are bigger now pretty much across the board, with some of the exhaust valves (I'm looking at you, cylinder 2) pretty wild.
 
Always check clearances on a stone cold motor. Lose valves can be noisy. They sound like a typewriter. lose is better than tight though, you may lose a little performance but you don't risk engine damage.
 
On a stone cold motor - thanks mate. Engine wasn’t stone cold, pretty warm in fact. I’ll recheck them again today.


Sent from my iPhone using DO THE TON
 
Also, after doing some (admittedly online) research I've learnt that fine metallic powder in the oil after an engine rebuild isn't entirely abnormal. Lots of parts in there all saying hello to each other for the first time.

And So, I shall, remain optimistic.
 
It can look like sort of a pearlescent paint luster when you mix the oil up in the drain pan. Clear oil should separate to the top almost immediately. If it's looking more like metal flake paint, obviously that is bad.
 
Yeah Irk, that's what it looks like - pearlescent paint luster. There was a fair bit of really fine metal powder in the filter housing, and some in the pan.
 
So my man Gabriel came by to have a listen. I've talked about Gabriel before - he was a Honda motorcycle mechanic for many years before starting his own business restoring vintage bikes. He's pretty much the guy around these parts in that particular field. Bike fired right up, he ragged the throttle, gave me his verdict - sounds like a brand new engine. All I needed to hear.
 
don't forget to re-tighten the head studs after a heat cycle
 
Cheers Doc, I'll do that. Didn't know it was necessary, but makes perfect sense - guessing the heat causes everything to expand a little so they'll need re-torquing? By the way, do you mean the studs themselves, or the stud nuts?
 
I can't believe I missed out on all this progress, I felt your pain when you dropped the cam tensioner nut into the motor :/ there just arent enough swear words to explain it, good save though, hopefully with the flecks in the oil its no biggy, I changed the oil a couple of times after rebuilding it, ran the motor for about an hour all up dropped the oil and put some more it, rode it a couple of times then changed it again. I did that on the advice I got from one of the fitters at work, said with a rebuild there can be debris that you want to wash out with the first lot of oil.

Pretty sweet to hear her running but
 
Ha, I think I've succeeded in making this thread pretty easy to miss. Burying it in the wrong section to start with (Restorations? Nope, no idea what I was thinking), and then taking two years so far with the build - I'm making it hard for you guys to stick around. Still, trundling along...

Along with the (admittedly much needed) validation yesterday that all my work on the engine had not been in vain, I also learnt how to check if the accelerator pump passages are working correctly. Thought I'd share, although I'm yet to try it out - I'll do so today and will report back. As many of you know, when you crack the throttle on these bikes (with these Keihin carbs) a nozzle in each carb throat will fire a jet of gas straight into the combustion chamber, a proper rip snorter. That is actuated by the accelerator pump shaft being pushed by the throttle assembly linkage on the carb body, which then sends gas through the passages to the nozzles. So, to make sure those passages aren't blocked, remove the accelerator pump housing from the bowl on carb two, in there you'll see the pump diaphragm and a small o ring. Load up the small hole in that o ring with WD40 (this is the hole that leads to the passages that feed gas to the nozzles in the carb throats), and then blast compressed air through the same hole. If the passages are clear you'll see the WD40 (mimicking the gas) firing out of those nozzles.

There's also a way to check if the accelerator pump itself is working, but to be honest that info didn't register. Something along the lines of depressing the accelerator pump shaft and seeing a fountain of gas - this indicates the pump is working (I'm just not sure where that fountain is. One way to find out).

So I'll pull the carbs, check those passages and also the pump. Turns out the labouring noise I heard from the engine is being caused by not enough gas going into the cylinders. Also, when I crack the throttle, no gas (or very little) is spraying out of those nozzles.
 
Jimbonaut said:
Cheers Doc, I'll do that. Didn't know it was necessary, but makes perfect sense - guessing the heat causes everything to expand a little so they'll need re-torquing? By the way, do you mean the studs themselves, or the stud nuts?
Click to expand...

yes the nuts.I usually back them off a tiny bit and then re-torque, that way you avoid a false reading. do one at a time in the correct order. the engine will have had to been properly hot to get the full effect of this, not just idling for a little bit.
 
Jimbonaut said:
Ha, I think I've succeeded in making this thread pretty easy to miss. Burying it in the wrong section to start with (Restorations? Nope, no idea what I was thinking), and then taking two years so far with the build - I'm making it hard for you guys to stick around. Still, trundling along...

Along with the (admittedly much needed) validation yesterday that all my work on the engine had not been in vain, I also learnt how to check if the accelerator pump passages are working correctly. Thought I'd share, although I'm yet to try it out - I'll do so today and will report back. As many of you know, when you crack the throttle on these bikes (with these Keihin carbs) a nozzle in each carb throat will fire a jet of gas straight into the combustion chamber, a proper rip snorter. That is actuated by the accelerator pump shaft being pushed by the throttle assembly linkage on the carb body, which then sends gas through the passages to the nozzles. So, to make sure those passages aren't blocked, remove the accelerator pump housing from the bowl on carb two, in there you'll see the pump diaphragm and a small o ring. Load up the small hole in that o ring with WD40 (this is the hole that leads to the passages that feed gas to the nozzles in the carb throats), and then blast compressed air through the same hole. If the passages are clear you'll see the WD40 (mimicking the gas) firing out of those nozzles.

There's also a way to check if the accelerator pump itself is working, but to be honest that info didn't register. Something along the lines of depressing the accelerator pump shaft and seeing a fountain of gas - this indicates the pump is working (I'm just not sure where that fountain is. One way to find out).

So I'll pull the carbs, check those passages and also the pump. Turns out the labouring noise I heard from the engine is being caused by not enough gas going into the cylinders. Also, when I crack the throttle, no gas (or very little) is spraying out of those nozzles.
Click to expand...

This is what Sean G's carb rebuild manual says as well .... you should push down on the accelerator pump shaft and gas should come out of 4 llittle valves on thee pump body.

but, one thing i am not following .... where is the little o-ring? On mine there is just the diaphram, which itself is shaped like mickey mouse, with the two ears acting as a seal .... or so i thought. I will get a pic tonight
 
Don't forget, there's an adjustment with the accelerator pump. You can actually time it by bending the arm that pushes the rod. There's another adjustment underneath on the stopper. Also, you can bypass the air cutoff valves, if you want. These carbs were lean from the factory and the air cut offs richen them up on decel.
 
Thanks for the info Irk - I'll look into that when I pull the carbs and work on that pump. I had the opportunity to delete the air cut-off valves when I split the bank yonks ago to clean them but passed it up. They'd be a right pain in the arse to get to now so they'll stay.

Worked on the front fender today. I've already cut it fore and aft but wanted to lower it closer to the tire. Dropped it by about 10mm, drilled new mounting holes and had to relocate the bracket for the brake line. While I was at it I made a new bracket for the other side, welded it all up, cut the lower mounting holes off - happy with the look.

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Thought I'd share this really useful trick I learnt a while back. Found out that I'd forgotten to clean out the fender mount threads on the lower fork tubes, and so couldn't bolt the fender in. With the fork tubes off the bike it's an easy job with a tap, but inaccessible with the forks on the bike and the wheel in the way. Get a sacrificial bolt (same diameter and thread pitch as the one you need) and cut two grooves down the length on opposite sides -

hZaebYel.jpg


Then thread that bolt into the hole using a wrench, backing it out every now and then and clean out the crap in the grooves -

klTALxPl.jpg


Works great in tight to reach places or when you can't use a die or don't got one.

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I also did another valve clearance check on the cold engine as suggested. Clearances were a little tighter and almost all of them within spec. Exhaust 2 are a little loose, but better that than the other way round.
 
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chickenStripCharlie said:
one thing i am not following .... where is the little o-ring? On mine there is just the diaphram, which itself is shaped like mickey mouse, with the two ears acting as a seal .... or so i thought. I will get a pic tonight
Click to expand...
I'll need to pull the carbs to be sure - when I do I'll upload a photo
 
By the way, this is the master cylinder I bought. It's a Nissin Retro model. Really solid and well made, looks good too. Bought mine from webike.net in Japan, best price I could find online

2p1JKSJl.jpg
 
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