Honda CB750K5 Restoration by Royhall

[royhall]

Following holidays and an extended period of illness I have got back onto the 750 only to discover a bit of a snag. I have jumped forwards a little bit here but bear with me. I was just fitting the oil tank side panel and removed the cap/dipstick to get it in and I noticed that the dipstick was dry. The oil tank was filled about 4 weeks ago and it appears that roughly half the tanks contents have found there way into the sump. I have removed the sump plate with the tank still half full and dried around the area with tissue. At the moment it's still dripping a bit from the oil on the castings, will leave it overnight then see if I can spot where it's coming from. Is it even possible to connect the hoses reversed, I don't think it is. I fully rebuilt the pump when I did the engine, am beginning to suspect a mistake somewhere. Any ideas will be welcome. Cheers.

[Bryanj]

Sounds like the valve in the pump is leaking a bit, always was a thing on 750's stood for a while

[royhall]

That was my first thought Bryan but it was rebuilt with all new seals. I'm Hoping when the surrounding castings have stopped dripping and dry out that I will be able to see where the leak is coming from. I'm hoping that I didn't damage anything when I changed the centre seal as it was a bit hard to get out. I think that would cause the leak to be coming out of the filter screen.

[Skoti]

Mines does that when parked up during the winter months.
I just drain the sump and pour the oil back into the oil tank through a straining filter.

I believe the term for this is "wet sumping", common on British motorcycles.

BTW
Did you replace the valve plunger seal 15166 300 000 with a genuine Honda one or an aftermarket version?

   

[Trigger]

Following holidays and an extended period of illness I have got back onto the 750 only to discover a bit of a snag. I have jumped forwards a little bit here but bear with me. I was just fitting the oil tank side panel and removed the cap/dipstick to get it in and I noticed that the dipstick was dry. The oil tank was filled about 4 weeks ago and it appears that roughly half the tanks contents have found there way into the sump. I have removed the sump plate with the tank still half full and dried around the area with tissue. At the moment it's still dripping a bit from the oil on the castings, will leave it overnight then see if I can spot where it's coming from. Is it even possible to connect the hoses reversed, I don't think it is. I fully rebuilt the pump when I did the engine, am beginning to suspect a mistake somewhere. Any ideas will be welcome. Cheers.

It is normal Roy. Some people call it sumping but, sumping is when all the oil goes to the sump.

Just start the bike up and it will return to the tank and once the tank is full again, ride away 

[royhall]

Thanks Trig. Whilst the sump plate is off I may as well double check that nothing is stuck in the relief valve.

Sent from my Pixel 7 Pro using Tapatalk

[Trigger]

Thanks Trig. Whilst the sump plate is off I may as well double check that nothing is stuck in the relief valve.

Sent from my Pixel 7 Pro using Tapatalk

If you have the sump off, take the cap off, remove the spring and turn the plunger with your little finger to make sure it is nice and free, and not catching.

[royhall]

Mines does that when parked up during the winter months.
I just drain the sump and pour the oil back into the oil tank through a straining filter.

I believe the term for this is "wet sumping", common on British motorcycles.

BTW
Did you replace the valve plunger seal 15166 300 000 with a genuine Honda one or an aftermarket version?

 

Yes I replaced all the seals in the pump. The kit came from Trig/Julie so is probably a well tested reliable kit.

Sent from my Pixel 7 Pro using Tapatalk

[Martin6]

Following holidays and an extended period of illness I have got back onto the 750 only to discover a bit of a snag. I have jumped forwards a little bit here but bear with me. I was just fitting the oil tank side panel and removed the cap/dipstick to get it in and I noticed that the dipstick was dry. The oil tank was filled about 4 weeks ago and it appears that roughly half the tanks contents have found there way into the sump. I have removed the sump plate with the tank still half full and dried around the area with tissue. At the moment it's still dripping a bit from the oil on the castings, will leave it overnight then see if I can spot where it's coming from. Is it even possible to connect the hoses reversed, I don't think it is. I fully rebuilt the pump when I did the engine, am beginning to suspect a mistake somewhere. Any ideas will be welcome. Cheers.

It is normal Roy. Some people call it sumping but, sumping is when all the oil goes to the sump.

Just start the bike up and it will return to the tank and once the tank is full again, ride away 

That's the beauty of a full unit construction engine and gearbox. If you do that on old British bikes, you risk blowing crankcase to primary seals.

Out of interest, do these motors solely rely on oil pump tolerances to keep oil in the tank? No in line anti-sumping valves, etc.?

[Martin6]

Just read the thread end to end. You've done a wonderful job Roy. We'll done.

[royhall]

Thanks Martin. It spurs you on when you know people out there are appreciative of what your trying to achieve.

[royhall]

Finally managed to get back on with the job. The first couple of pictures aren't exciting but it may help someone at some point. The bike had the American driven safety unit in the wiring. The purpose for this is to prevent the bike being started unless the gearbox is in neutral and the clutch pulled in. The unit with the bike was in a poor condition after water had got into it and it was impossible to find another.

[ Guests cannot view attachments ]

As I'm not a complete imbecile I decided that I could probably manage to start a bike without killing myself or anyone else, that I would do away with the wretched thing. I could throw it in the same bin as that bloody beeper on the indicators. The bypass wiring turned out to be very simple. I just had to make up a little patch cable with two male spades and fit it as the picture. Simples.

[ Guests cannot view attachments ]

After sorting out the mess that is the headlight wiring I could hopefully move on to fitting the headlight and the completion of the wiring. Always a nice point to get to as wiring is not my strongest skill, especially with the non standard items fitted. After getting everything working I shortened some of the wires and made sure everything was insulated properly. You will note from the picture that space in the headlight is tighter than usual due to the indent in the shell. This is on USA bikes to fit that horrible indicator bleeper, or as I see it a complete waste of much needed space in the headlight. After sorting the wiring, I fixed some of it to the back of the shell with Gorilla tape (crikey that stuffs sticky) that made fitting the headlight easy peasy.

[ Guests cannot view attachments ]

[ Guests cannot view attachments ]

What came next was another reproduction part shocker.

[royhall]

Apologies, on the last post I used the same picture twice. Old people eh, what can you do with em!!!

[Bryanj]

Listen to the wisdom mate

[royhall]

For the headlight I bought a sealed beam unit and a replica rim from Silvers as the original headlight not only dipped the wrong way but was also cracked. I built up the mounts onto the headlight unit then tried to fit the replica rim. It was difficult with nothing lining up correctly but I sort of managed it. Then when trying to fit the headlight the rim was nowhere near fitting the bowl. As usual a repro part that wasn't worth the effort of making it, another £40 wasted. More importantly I couldn't fit the headlight. As the original was a manky mess I decided I would fit it whilst I found another and got it chromed. After giving it a good clean with Solvol the thing came up like it was brand new (just look at it in the picture), wish I had looked closer in the first place. Anyway, the headlight built up and fitting correctly in about 10 minutes. Result.

[ Guests cannot view attachments ]

So that's the electrics finished. I went round trying everything and it was all working correctly. Obviously as the engine is not yet running I cant check if the battery is charging or the ignition. That's for another day. Next up I have some large boxes that have been lurking in the corner of the garage for well over a year.

[ Guests cannot view attachments ]