Topic: Honda CB750 K1 barnfind after 40years lots of patina

[rinkeldekinkel]

Hi

I recently found a 1971 K1 750 that was ridden from
71 to 75and than stood in the shed for 40years upto now
I know the owner via my best mate, he lives verry closeby
So we heard the complete story that came with it.

To be short, it was purchased new in Haarlem, the very cool
Then Ducati dealership plate is still on.

He rode two up with it on holidays fast, so after short time he desided to have a good local
Welder box the rear swingarm, i must say it looks really proper, the seamwelds are taken off
And all sections received a full steel strip, he decided to put Koni shocks on the rear and a
Steering damper on the front.

He has put it away in 1975 and not touched it since,

unfortunately the shed was not completely dry, so surfacerust is everywere
Even the tank is so thin on the top that it is rendered useless,
However to keep the patina i might be covering an ebay tank with this tank for right patina.

The engine is stuck, and 1 plug broke clean off so i will remove the engine, and
Do a clean lube and hone, and might do all tensioners and chains asswell.

I will post some pictures of the progress i made
Soon, because i had to cut the headerpipes as they would not come loose.

[CycleRanger]

Nice find! Looks like the bike is all there. It should make a good project.

[Sgt.Pinback]

Nice find. Sems to be a German or Netherland K1. Does it still have the "HMCB750" pipes?

[rinkeldekinkel]

Yes the hmcb750 mufflers are there, i had to cut the headers
Unfortunately because the could not be removed at all.
I also have a 341 set with the shorter inner damper
I will repair one of these kits and mount them.

[nvr2old]

Wow..the red line on the tach is even still red...

[Sgt.Pinback]

Yes the hmcb750 mufflers are there, i had to cut the headers
Unfortunately because the could not be removed at all.
I also have a 341 set with the shorter inner damper
I will repair one of these kits and mount them.

That's sad because the "HMCB750" are very rare and had been used only on  European KO and K1 such as Germany, France and Netherlands.  Allmost sound as the "HM300" pipes.

 Where  do  you live?

 Nevertheless nice project!

[754]

I would have undone the spigot before cutting the pipes..

[rinkeldekinkel]

Hi,

Believe me i really tried, but the countersunk screws where stuck
As concrete...

I could still weld the mufflers back together, alternatively
I could put new headers bare steel on them, but the patina
Hmcb750 look the best in terms of the patina

I am lucky to have a ac dc tigwelder, so it will be barely noticable

 

[rinkeldekinkel]

took the engine out of the frame last night, it was a good amount of work to get the spigots drilled off.
taking the engine out is relatively simple with a pillow for the engine, and put the bike on its side..

hope to be able to dismantle the engine this sunday to know what to replace...

this is the stage where painting the frame and rearfork is real easy....... F%^& i am tempted.....

A question, the weld on one engine mount as you can see in the attached picture, is terrible, but original.... why??? is this common that they ran out of CO2 Argon?

[CycleRanger]

Crappy welds are typical on the early 750 frames.  They were in a hurry to make money!

[MCRider]

In my limited experience, breaking a plug is the result of using a wrong sized socket. Not so much where the wrench engages the plug, but along the shaft over the top end of the plug. It should be really skinny and hopefully contains an insert of foam to stabilize the ceramic of the plug. Erstwhile it will sit on the plug at an angle and snap the top off.

Or, it just broke.   

[rinkeldekinkel]

The plug just broke;)
It was rusted stuck, just like the cylinders.

Today I cleaned the engine with s100 degreaser in the carcleaning shop
With a 60 degrees medium pressure cleaner.

It came out very clean, and much nicer to work with.
Cylinderhead cam off real easy but the pistons are stuck as hell!!
Ive soaked them in a special penetrating oil hope they will come loose
Next time
otherways ill try atf acetone like many of you suggest

Am i correct to think that if they will notcome unstuck, i can remove the
Bottom case and remove the rods?

[Stev-o]

Am i correct to think that if they will notcome unstuck, i can remove the
Bottom case and remove the rods?

No

[rinkeldekinkel]

Pistons have become undone, had to heat them up pretty high
I heated them with my oxy torch without result, second time
I hit the pistons with 220 amps with a tig acdc welder.
They where loose in a jiffy

Unfortunately two threads of my mainbearing bolts came out on the bolt...
Is that happening more often ? Will a good installed helicoil help?

The conrods where pretty rusted also, i have cleaned them, unfortunately
They have some slight pitting still.

At least two of the conrod bearings have some seizing markings.
One has some inclusion of "foreign material " in it and one crankbearing has a scratch

What should i do with the scratch, i know there are always two
Kind of mechanics the oned leaving old bearings alone, and the ones
Replacing every one of them.

Also my oilpump leaves me with questions, it has seen some debri, but the fit is still very tight, the 0.10mm barely fits between rotor tip and rotor, 0.05mm barely fits between the housing and rotor
Honda out of spec is 0.35mm
New rotors are not available, so i think i will have to live with this damage
They turn smoothly after some very fine polishing

Ill be glad to hear from yall.

[Tews19]

Subscribed! You seem to be moving pretty fast on the project!

[calj737]

Replace the bearings. All of them. It looks as though the motor was stored with almost no oil in it? Member Elan has an oil pump rebuild kit (no rotors, yours seem fine) but all the needed O-rings and screen.

[oldhatt45]

rinkeldekinkel,

Have you got Hondaman's Book?
If not I would suggest you get a copy.  It will answer your question about the oil pump  and other questions you haven't asked yet. 



Charlie

[70CB750]

rinkeldekinkel,

Have you got Hondaman's Book?
If not I would suggest you get a copy.  It will answer your question about the oil pump  and other questions you haven't asked yet. 

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