Head Bolts

[Martin6]

Hi, would welcome some further advice, please.

I had a minor blow from the head gasket, which became a small drip whenever I stopped and popped it on the side-stand. I investigated the nuts visible next to the spark plugs. One of them (next to cyl  no.3) was so loose I could turn it with my fingers. Cyls 2 and 4 were also not very tight. When the previous owner bought my bike, he found a handwritten note stating the piston rings had been replaced. The bike has done 650 miles since then. I'm guessing it has settled and requires a re-torque. That's my experience with old British twins, don't know if that happens on the CB750?

I've tightened them up and I think it is much improved. I would also like to check the rest. Is it possible to check and tighten the remaining head nuts, without removing the engine?

Thanks,

Martin

[Nurse Julie]

The CB750 rocker cover will not come off with the engine in the frame. And the bolts ( not bolts as they have studs with a washer and nut on ) must be tightened in a pattern and should never come loose .

[Bryanj]

As Julie said Honda specified a pattern and torque for the head nuts and did not specify a re torque.
Having said that some of our US cousins like to leave the engine for 24 hours and re torque anyway as, also as Julie says the rocker cover can not be removed with engine in standard frame

[Martin6]

Thankyou both.  Yes, that's what I understood, was just hoping for a miracle!

Also, I know about the tightening sequence, but my feeling was, on balance, leaving the nuts loose was more likely to warp the head, than tightening them, especially as the nut close to cylinder 1's spark plug was fully tight.

Further investigation, I was cleaning up the front fins using compressed air to blow out engine degreaser. In the corner of my eye, I saw something vibrate. It was the top of a bolt I'd not previously noticed. It is completely free. I think it has sheared. Initially I was puzzled, as I can't see the bolt mentioned in the factory service manual, but I found a brief mention in the Haynes book and to a similar one at the rear of the head: "Do not overlook the two small bolts in the centre (front and rear) of the cylinder head." I am now feeling a bit dejected! What do they say, "buy in haste..."

I am desperately trying to avoid engine out. I don't think I have the skill to tackle something as complicated as this motor. I've done a lot on my Norton, but not full engine surgery. I've only done that on a small 2-stroke, which is a much easier proposition. Once the engine's out, given some of the things I've found and the mileage (40,000), it would deserve a thorough inspection and a fair bit of preventative work. Probably the cost of sending it to someone trustworthy, if I can find someone, is likely to be beyond me at the moment. I was hoping for 1 or 2 seasons of riding, before getting to major jobs... Not sure what to do.

As the weep is fairly minor, at the moment, I'm tempted to just ride it and save up for work to be done over the winter, either later this year, or next.

[Bryanj]

If you can work on a norton you can do a honda.
Download the honda manual, get a 3/8 drive six sided socket set, cirlip pliers and torque wrench plus a mate to help lift the engine out.

[Martin6]

Bryan,
I've got the manual and that's what's putting me off! 

[McCabe-Thiele (Ted)]

My Honda 400 rebuild during COVID lock down  was the first time that I had worked on a bike since 1969. Never split a crankcase yet along worked on a 4 cyl motor cycle only on cars and gave up on  car engines 35 years ago.
There are videos on U tube plus loads of members here who will lend their experience and advice f.o.c.
You are never too old to learn new skills if you have the time.
Take plenty of pics on your phone and get that engine out !

[Matt_Harrington]

Bryan,
I've got the manual and that's what's putting me off! 

Manuals are always daunting! Bryan is right and it will never be as bad as you thought it could be.
I'd be a bit worried about running the engine and creating damage that may cost more in the long run.

[SeanFD]

You can do it if you're at all reasonably competent with a spanner.

I did a nut and bolt restoration of my 750 that had sat in boxes for 30 years and my only previous experience was on a CB125S back in 1976.

Apart from all the advice and support you'll get here, have a look at these videos; I found them very useful.

https://www.youtube.com/watch?v=MkHJuU01-Wk

Ignore the "cafe racer" bit, its a CB750 total rebuild – in 40 episodes.

He's not infallible, but honest enough to admit a mistake if he makes one; I pointed out and error and a week later he had added a comment to the video.

[Sesman]

Get stuck in lad. You will learn loads and you are not alone. Both your character and confidence will be buoyed. Now as for your bank balance…..😁🫣

[McCabe-Thiele (Ted)]

This series was my mentor on the 400 - some gaps in detail but was a real help.
I switched on the captions and would pause at what seemed like complicated stuff.
When unsure I would post pics & ask here - yes some jokes but the feedback from a handful of members was invaluable.

https://www.youtube.com/watch?v=NQgwhv8v6Os

[Laverda Dave]

Go for it, you will be suprised how easy it all is once the engine is out. I would rather work on a Honda than my Triumph twin any day

[Martin6]

Wow! Pretty unanimous that I should give it a go. It's definitely daunting. At the moment I'm getting over my disappointment.

I guess, running it, I have the risk that if the head is not warped, it could warp over time. It runs sweet enough now. It's not using oil, just a couple of drips onto the floor off the front left fin, when on the sidestand after a run. That's what alerted me. I've since noticed a slight film on the engine cases, now im looking for it. But not bad.

I guess in part it's confidence. Am I skilled enough to measure all the tolerances (bearing shells, valves etc.)? What do I do if the head is warped? Am I capable of removing and replacing the key bearings? Will I know what a worn gearbox looks like... etc. Oh, and the hardest one, how do I explain it to my wife 

Then there's the list of expensive bits I might find. Plus the bits I should change as I'm in there and 40,000 miles may not be the end of life, but I don't want to go back in there shortly after. Things like I guess, I should change the cam and primary chains after 40,000 miles, probably everything rubber, like the tensioners, valve seals?... As I say, a bit daunting. Then there's special tools. Engine stand at the least. I'm guessing, but parts alone could easily be over £1,000? 

Feels like a big decision.

[Nurse Julie]

Enjoy it for the summer and thick about it again once the dark nights roll in. Trigger has tons of experience on 750K engines and i will add them up one day but it runs in to hundreds. There is thing that the manual's do not tell you about these old engines and how to seal them correctly.   

[Bryanj]

All the ones i built in dealers were done on the bench, no stand.
You need a clutch nut special tongued socket, but if its ever been off bet it was butchered with hammer and punch.
You need an alternator rotor puller, which is a bolt with the correct thread.
Main and big ends you can normally say if they look good they are but you can use plastigauge to check.
You do need a decent torque wrench, preferably 3/8 drive as there are plase 1/2 inch drive sockets wont fit.
Hondabond and graphogen will probably be the most expensive non honda part.
Yes all rubber bits, they have been getting rock hard for decades.