CB500 K1 Rebuild

[Charlie J]

Just getting started on rebuilding my project Honda Four which I introduced in the new members section. The confusing Subject title is due to the fact that I don't as yet know quite what I've got. The crankcase is stamped CB500 whilst the cylinder block has 544cc stamped on it. I thought from info from David Silver spares that it was a K2 but BryanJ tells me we didn't get a K2 in the UK and it might be a K1.

Anyway, it is what it is and I'll see what I can make of it. First job was to see if I could get the engine running after the bike had been left in a shed for at least 30 years.
So jobs done so far;

Stripped and rebuilt carbs which as you would expect were completely gummed up. New needle, jets, gasket, airscrew etc. The biggest problem was trying to fit the non-shaped o-rings. I had to resort to the use of super glue in the corners to get them to stay in place

New plugs, point and condensers

New oil and filter

Static timing set

Valve clearances adjusted

Timing chain adjusted

Rigged up basic ignition and starter circuit wiring (a lot of the original wiring is missing/damaged

Rigged up temporary fuel supply

Connected to booster start battery charger

Hit my makeshift starter button

The bike fired up immediately  I almost danced a jig. What a wonderful feeling, but it didn't last long. The bike dumped half her oil on the floor, used 2 pints of petrol in 10 seconds and filled my shed and the surrounding neighbourhood with exhaust smoke.

Back to the drawing board. Traced the oil leak to the bolt inside one of the side covers on the cylinder head cover and got that sorted. The disappearing petrol was coming out of the overflow of all four carbs. When I rebuilt the carbs, I set the float height to the specified value of 22mm which just didn't work, I ended up with a height of 26mm using the clear tube method. Fired her up again on the button and the bike is running well but with clouds of grey exhaust smoke. Checked the cylinder compression and it's about 135 psi on all 4 cylinders which I hope is good enough. Next job is to change the valve stem oil seals whilst leaving the head on to see if that sorts the smoke problem.

[Nurse Julie]

Sounds like fun 😁😁😁😁

[hairygit]

550 barrels on a 500 bottom end was a popular upgrade back in the day, but it involved machining the crankcase mouths out to suit the larger diameter liners. You'll have a lot of fun with that bike, nice little middleweight that handles nicely. Never, ever stamp on the gear lever to shift down, the forms are easy to damage, probe to bending, and near impossible to get now at reasonable prices. Welcome by the way!

Sent from my POT-LX1 using Tapatalk

[SPR]

Remember to do the compression test with throttle wide open ....

[Charlie J]

Remember to do the compression test with throttle wide open ....

Thanks SPR. Throttle was wide open.

[Charlie J]

Just trying to post an update on my project but don't seem to be able to attach photos. So this is just a test. Apologies in advance. [ Guests cannot view attachments ]

[Nurse Julie]

Great photo 👍👍👍

[Charlie J]

Well I managed to attach a photo of the bike so I'll continue with the update. As I said in an earlier post , after getting the engine started amid clouds of exhaust smoke, I thought I'd try an easy fix of changing the valve stem oil seals with the engine in the frame and the cylinder head in-situ. I removed the rocker cover to find that it was in a pretty bad state with bits broken off.

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I'll try and get these areas repaired the best I can. You can also see in the photos that the tappet caps have seen some treatment from a hacksaw in the past in order to sort out where they had been rounded. I had to use  15mm, 16mm and 17mm spanners to remove them! 
 There is also an irregular shaped hole which I don't think should be there.

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I don't think it does any harm, unless someone can tell me differently? The tachometer drive also looks beyond repair.

I used a Sealey VS1542 Valve Collet Remover/Installer
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to remove the valve springs so I could replace the oil seals without removing the cylinder head. I was a bit apprehensive about using it as I had read some reviews that said the tool was fine for removing the collets but not so good at reinstalling them. However, the tool worked a treat for me. The only slightly tricky part was dealing with the exhaust valves on cylinders 2&3 because of the proximity of the posts for the fuel tank mounting rubbers. But a sharp tap, square on with a 2lb hammer did the trick. I also used the string down the plug hole and rubber band tricks which I read about on this forum. I can't remember who posted them but many thanks anyway.

I reassembled everything and used the damaged rocker cover as it was just to see if the oil seals had done the trick. The bike fired up immediately accompanied by clouds of exhaust smoke. So much for an easy fix! I'll take the head off next and see what that reveals.

[Charlie J]

So, next stage in the rebuild was to remove the head and cylinder block to try and identify the cause of the smoking exhaust. I think the photo speaks for itself. [ Guests cannot view attachments ] There is significant pitting to the cylinder sleeves. I’ve checked the cylinder bores and they are standard 58.5mm for the 550 head (which is fitted to the 500 bottom end). It looks to my inexperienced eye that a fairly deep cut will be required to remove the pitting, possibly requiring the 3mm oversize pistons available on eBay from Cruzinimage. A 3mm rebore seems a lot to me, does anyone have any views on this?

I also have a spare 500 cylinder block with standard 56mm liners. The liners have a light coating of rust and two vertical scratches in one of the bores that are just detectable by a finger nail.

This leaves me with a number of options and I can’t decide which is best so would welcome any advice.

3.0mm oversize for the 550 block with new pistons etc

Minimum possible rebore for the 500 block with new pistons etc

2.5mm rebore for the  500 block and reuse the existing pistons with new rings

There may be a problem with using the 500 block because as Hairygit pointed out in a previous reply, the 500 crankcase has been machined to accommodate the larger diameter liners of the 550 block. There is only about a mm or so difference but I don’t know if this will cause a problem, so again, any advice will be greatly appreciated.

[Bryanj]

My email is in my profile, send me some pics of the base gasket area on crankcase, the later cases had big enough holes from Honda to take the 550 cylinders.
3mm over is a lot but there are so called 605 kits with liners out there, lots of options.
Mail me and we will discuss it

[Charlie J]

So, following some gratefully received advice from BryanJ, I’m going with a 550 cylinder block with a 0.5mm oversize rebore. Not only did Bryan help me out with his expertise, he also offered to do the rebore for me. How good is that!

Whilst waiting for the rebore to be done, I took the sump cover off to have a look at the primary drive chain. As can be seen from the photo, any hopes of good news soon disappeared.
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The chain has a huge amount of free play and has been chewing its way through the crankcase.

 Just got the cases split after whacking with a rubber mallet for 10 minutes before I discovered the ‘secret’ bolt in the sump area! Next job is to take a look at the crank bearings, but following my discoveries so far, I’m not too optimistic about them being in good shape. Oh well, all part of the fun as they say.

[Charlie J]

I’ve also learned how to nail a cup of coffee to the ceiling 

[Erny]

[Bryanj]

That looks quie clean in there so bearings could well be OK. Remember to keep the shells where they came from as you will not be able to identify the size if you mix them up

[Charlie J]

Thanks Bryan

Will do.