Head Bolts

[Martin6]

Everything is back together. Bike started 2nd attempt. Oil light out within a couple of seconds. I warmed it up, varying the revs. No oil leaks so far. I still need to balance the carbs, I spent time getting them as close as I could before mounting them on the bike. It seemed OK at 1400rpm, but not especially smooth below that. I didn't idle it for long though.

I replaced a lot of the head nuts, bolts and screws and engine mount hardware, repainted the engine and had the frame and brackets powder coated, whilst the engine was out. I also found the cause of my stiff front suspension, a slight bend in one of the stanchions. So I replaced that and the fork oil seal. New Hagons on the rear.

It's looking quite tidy. Fingers crossed it will run well. I'm aiming to go for a run tomorrow in the sunshine. Maybe get 30 miles on it and check it over a few times. I'm thinking I'll change the oil and filter at 100 miles. Does that seem sensible?

Martin

[Skoti]

Defo change the oil and also would recommend dropping the sump plate to inspect the oil pump strainer gauze for particles of surplus gasket sealer etc.
If you find lots of stuff in there then pull the oil filter for inspection as well.
 With Honda engines cleanliness is next to godliness!

Good luck

Skoti

[davidcumbria]

Congratulations on completing the rebuild - sounds like you have done a good job.your having  the cam timing corrected should make a very appreciable difference. Compared to everything else oil is cheap so there is no real downside to changing the oil conservatively and it’s good for peace of mind.

[Pauarc]

Hi Martin
it’s great to hear bike back together hope the first run out goes smoothly good luck Paul

[Laverda Dave]

Well done on the rebuild, what a Christmas present to have 🎄.
I would change the filter as well as the oil even though it will only have 100 miles on it, for the sake of a tenner it worth it for piece of mind and it gives you the opportunity to inspect it for any contamination.

[Martin6]

78 miles. Ran almost faultlessly, after I tightened the rocker caps! No other oil leaks. The bike is definitely punchier and the suspension feels good, much better at absorbing bumps and no bottoming out. Perhaps a little underdamped at the front, but I'm not complaining. It was a very enjoyable ride.

A friend saw no smoke, except at one point when I opened up to accelerate hard, producing a whiff of black smoke. Running rich maybe?

Couple of questions:

I've a slight hesitation applying the throttle from tickover and a bigger hesitation if I rapidly whack the throttle on whilst riding (c.3500rpm). It's fine if I just roll the throttle on in a more measured way. Are these symptoms of running too rich?

I seem to have a wandering oil level on the dipstick. Was at 80% when I started out. Was just above the minimum 40 miles later, then at 75% when I got home. All readings were taken on the centre stand,.on level ground. Oil return looks consistent when I check in the tank. For the last of the readings, I put it on the sidestand before lifting it onto the centre stand. Can't see how that would affect the tank level though? In your experience, is this odd, or usual behaviour?

Minor observations:
I'm not convinced the tacho is calibrated correctly. 1400rpm sounds and feels like a nice gentle tickover. Below that just feels too slow. I'm yet to do a running carb balance though. The speedo is definitely reading fast by more than I'm used to. I'd say indicated 60mph is really a tad over 50mph. A local radar speed awareness sign shows 30mph when I have 36 on the speedo! I'll live with that.

Thank you for encouraging me to give the rebuild a go. I have a huge sense of achievement and feel like this is now my Honda CB750, my 'pride & joy'! The manuals (Haynes and Honda) were good start points, but a bit tricky on model variations over the years. Most problems I stumbled into were solved without too much drama, via searches here and on SOHC4 forum. Only a little blood was shed in the process!

I'm looking forward to next year with my bike, although with my fingers crossed for now.

👍 Best,
Martin.

[McCabe-Thiele (Ted)]

Well done getting a run out before Christmas - sorry can't help you on 750 oil levels my bikes are standard wet sumps.

[Johnny4428]

Great news Martin! So impressed you managed out this time of year for a “shakedown” run. Wouldn’t be too concerned about the oil level, I’ve had that on my 750, after all the engine is where you want the oil to be not the tank. Well not all of it anyway. Bit of syncing and tuning to do by the sounds of it but plenty of winter ahead yet!🥶

[Martin6]

Great news Martin! So impressed you managed out this time of year for a “shakedown” run. Wouldn’t be too concerned about the oil level, I’ve had that on my 750, after all the engine is where you want the oil to be not the tank. Well not all of it anyway. Bit of syncing and tuning to do by the sounds of it but plenty of winter ahead yet!🥶

I'd guess it's a little bit warmer and a lot dryer down here! I'm able to pick my days and ride all year with a few mates. Bacon and eggs are a great winter warmer! Although, some of the winter runs, I stick to a modern bike with a big enough alternator for a heated jacket.

I was out again today, warmed the engine through and up to nearly 100 miles, so I could change the oil. I'm really pleased, it was lovely and clean and I dissected the filter, which was also clean. I'd also unwound the air screw on carb no.1 by 1/8th of a turn. Initial impressions are it is better, but forgot to check the plug before restarting the bike to check new oil level. Still so far, so good  👍

[Oddjob]

Dissected the oil filter? Respect there Martin, not many would go to those extremes.

I ran with some really powerful magnets on the outside of my cannister filter, on my CB1300, around 6-8 IIRC, the idea was that any metal would stick to the outside of the cannister due to the magnets, when I removed the cannister I cut the housing in half so I could see if there was anything there, there wasn't. Saying that, alloy would not be attracted but you can't win all the time.

[Martin6]

No cannister, it's only a removable paper filter onnthe 750s. Just cut the ends off with a Stanley and unravel. Do it over the catch can though 

Edit: it's not diligence, more like lack of confidence I could have got it right 1st time!

[K2-K6]

The oil level can "appear" a little variable on the 750 in comparison to other non dry sump type bikes.

As long as you put in the correct volume at change of oil it won't give problems, but may initially give a little confusion.

The bulk of the oil should be in the tank (as any dry sump system will be like this) with as much supply volume available to the pump, and then onwards to galleries as possible.

Dry systems work on having greater volume through scavenge, back to tank, than delivery to always ensure oil available to pressure side of pump. Interupted supply (depleted tank reservoir) leads ultimately to catastrophic oil starvation in extreme cases.

Manual says run until warm, switch off, then immediately (it doesn't say immediately) but you don't need a "settling" time on dry sump system, to check running level in tank.
There's no dipstick in engine as oil should not be reservoired there.  If it is, then there's a fault and usually with stop valve that prevents flow from draining tank into engine while not running.

If checked after being out on a run, then left overnight and checked (before starting) again, with a drop between these two measurements you'd suspect the stop valve seals.

Usually dipping the tank at any point really should give virtually the same result, or very close in range. Big variation  and you'll need to  consider working on the pump to fix further potential problems.

[Martin6]

Thanks. I have a dry sump system on my 850 Commando, so I know about 'sumping'
This was variations whilst still hot. I'll watch it, but I think it's probably fine.

The thing I'm most nervous about is still having signs of the sooty plug on no.1 and a bit on no.2 and not taking off when i more aggressively whack on the throttle. I think that suggests it's too rich, but not sure about that?

Along with the bad oil leak, this was one of the reasons i took on the engine refurb. The carbs were cleaned out thoroughly with carb cleaner and compressed air. Needles on middle grooves, bench synch'd to get reasonably close, using a drill bit method. Air screws initially at 1 turn out. Float heights double checked with a vernier guage on the inner flat area of the bowl edge. New rubber seals on the carb tops. No sign of splits in the rubber manifolds.

Can timing is fine and points / ignition timing (also no.4 is running clean). Tappets were set carefully when the cover was off.

Not sure where to go on this? It's a pain cleaning the plug every 200 miles, which is what I was doing. I've had one thought, I didn't clean out the exhaust headers, which were sooty on 1 and 2. Is it possible the sooty plugs could be due to transfer from the headers? But that wouldn't explain the bogging down. All a bit confusing...

[Skoti]

Renew the needle jets and needles, that's what cured the sooty plugs on my F1 along with dodgy throttle response.
Although I first wasted cash on new main and idle jets which made no difference whatsoever.


Oh and BTW it's better to use genuine Honda needle jets and needles, after market stuff sometimes gives flat spots when accelerating as the needle profiles are not exact.

Good luck

Skoti.

[K2-K6]

Unless it's a very unusual circumstance or peculiarity, then sooting of combustion chamber is always simple excess fuel to oxygen ratio.

Unusual circumstance......we had on here a partly blocked header pipe that did similar. Effectively this prevents full exhaust of burnt mixture, to combine new intake fuel volume with oxygen depleted mix and give incomplete burn. This is what exhaust gas recirculation does by bleeding in carbon monoxide to reduce the burnable mixture (accompanied by reduction in fuel injected obviously) and provide reduced effective volume under light loading. Clearly undesirable if present here though.

First suspect is always the air passages feeding the idle circuit, if not absolutely clear then the idle circuit runs at full "choke" as soon as you start it. With no air....or substantially restricted supply....the carb venturi sucks at maximum demand through only the idle jet dipped in fuel of float bowl. This will play havoc with any setup logic. Absolute certainty is required on this circuit to stop it running you ragged.
Crude test to see what response you get is too wind those idle airscrew in and out while running to gauge if there's competent response from each one that's suspect.

More advanced...with help from friendly MOT tester.....get each pipe measured when bike is working temp. Looking at HC to assess the unburnt hydrocarbon content should build you a picture to at least understand where it currently is in mixture terms.

Bench sync is fine for how you are, it won't generally correct anything jetting wise...unless very seriously out of kilter anyway. I wouldn't look at that as suspect.