Topic: Project Keira - 1971 CB750 K1 restoration

[GLRoberts99]

My previous projects have been pre-war Triumphs, 1970 Laverdas, and a few other Italian classics. I've got an RC30, a CB1100RD and have built a CB900F race bike but this is my first foray into a "proper" Honda classic.

The bike is a US model imported into the UK last year after what looks like a year at the bottom of a lake. I'll post videos on YouTube of the progress which< due to the state of the engine, is slow.

I want to restore it to as close to original as possible but it has to be a bike that will be ridden so I'm not aiming for a concours show pony, but a useable classic.

Wish me luck !

Gareth

[newday777]

Welcome aboard Gareth
You have chosen a very crusty, albeit, a worthy project. It looks to have sat out in the desert southwest sun by the looks of that seat foam.
Does the motor kick over or is it frozen solid?

[Shtonecb500]

she is gorgeous...she is gonna be such a nice runner. Good luck.

[GLRoberts99]

Hi NewDay777

Thanks for the note. The seat pan is worse than the foam, but the tank is fine (surprisingly), and the exhausts will take a lot of work to repair as I can't afford (or find!) a cost effective HM300 replacement set.

Yes, the engine is completely seized and will require a lot of "persuasion" to move. Here's what I found when I took the head off....


G

[Magpie]

Lots of work ahead for you but the end result will be a great bike. The last motor I did looked like that and I had to take the conrods off the crankshaft and take the cylinder block to a friend that has a 10 ton press. It made quite a noise when the pistons broke loose of the cylinder. Cliff.

[PeWe]

Those bores needs probably +1.0mm overbore if stock.

I had a cylinder with less rust I thought I could use +0.5mm pistons. I had to replace 2  sleeves and bore it right. Those  pistons at lower position creating a swimmning pool.

A good historical job, save the historical artifact from Honda!

[Kevin D]

Welcome Gareth and Good Luck.
I admire your courage!
I also have a K1, my one and only, s/n 1067xxx, 11/70 build. Join me on a ride someday.

[GLRoberts99]

Update - Saturday 27th March.

Well after a glorious victory by the Scottish Rugby team over France on Friday night, I headed into the garage Saturday morning with a slightly fuzzy head. After the last photo I posted of the cylinders full of gunk, I fished all the debris out as best as I could, and put in my special magic formula penetrating oil. I covered the bores with some plastic sauce pots lids from an Indian takeaway I had the previous Tuesday to prevent the oil from evaporating, and left it for a few days to work and today was the day to see what had happened.

Well good news in that the oil made its way down all four of the bores and so I know there is communication, which TBH I didn't expect. The bad news is that I didn't expect it to work, and I'd removed the sump plate for cleaning so my nicely carpeted garage now has a purple penetrating oil stain.

I know I won't be able to rotate the crank and get the pistons free that way and so I decided to split the cases. All bolts were removed, carefully and in sequence, and I've now hung the bike upside down from the engine mounts so gravity can encourage the cases to part. The idea is that I will be able to disconnect the con rods and free the crank, leaving me with a barrel, four pistons and rods to contend with - and I fully expect to have to apply heat to get that all free.

Let's see !

[BenelliSEI]

Sounds like a plan! Carpeted workshop??

[GLRoberts99]

Update on the restoration is that I've got the cases apart and have cleaned up most of the internals. Some of the gears had surface rust and a couple of the bearings were frozen (they'll all be replaced as a matter of course). Next stage is to prepare for vapour blasting which to me means plugging off all the blind holes.

The barrels are still being difficult. I had to put the barrels onto my BBQ to heat them up, and after cooling the pistons with water, tried to "encourage" them to come out. Two did, two didn't, and I had to satisfy myself with removing those liners instead.

Final step this week was to clean up the valves and the cylinder head as there was a significant build up of debris on both. Good news is that the underlying material is in fine shape, so many parts can be reused.

[MauiK3]

Great start, keep us posted!

[BenelliSEI]

Excellent progress n a tough project. Thanks for sharing it.....

[GLRoberts99]

Gettin back onto the project, here are a couple of videos of where I've gotten to ;

There are more loaded that'll get published on You Tube over the next few days.

[GLRoberts99]

Well it's been some time since I posted about the project.

I've got the engine fully rebuilt and in the frame and am now getting all the brightwork sorted.

The bike is Valley Green Metallic but I can't find the paint code to give to my painter here in the UK - can anyone let me know what the RAL code is? Thanks.

I've relaced the wheels myself, which took ages because I've never done it before but the satisfaction of getting them to run true was awesome !

My swing arm is shot so I'm on the hunt for a correct replacement - all over here in the UK seem to be K2 and onwards.

[Shtonecb500]

nice work, excited to see this done.

cant wait until im not chicken #$%* to start tackling motors.

[HondaMan]

The K2-K6 swingarm will fit, but the chain guard attachment in the front of the guard may be different on your K1. Other than that item, the arms are the same.

[GLRoberts99]

The K2-K6 swingarm will fit, but the chain guard attachment in the front of the guard may be different on your K1. Other than that item, the arms are the same.

Yea, I guessed that would be the case, but the chain guard brackets (and in some cases the brake reaction arm bracket) are different to the K1. Only the rivet counters will care, but it would be nice to keep it as close to K1 as possible.