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Discussion Starter · #1 ·
Wrote a lot of this in my member intro but figured I should write a log as well, should at least be incentive for me to keep going if not also interesting to others and useful for advice :)

Picked myself up an almost complete non-running 1973 CB200 a bit over a month ago and have been working on it since. The bike was apparently "running about a year ago but spluttering due to badly set points" which I doubt, after seeing the state of the engine, and the fact that it was last registered in 1993... I've wanted to restore or modify/cafe a bike for a long time and the opportunity came up (I was actually planning to buy a daily rider...) so I jumped in headfirst without much of a clue or planning. I am learning a lot, having come into this project with minimal mechanical or electrical knowledge, and am enjoying myself so far, though of course there are frustrating times.

My plan at the moment is basically to take it apart completely, learn as much as I can while doing so, clean up every component and replace the faulty ones, and re-paint the frame. Then when I start putting it back together consider the cosmetics such as repainting/re-chroming (unlikely due to cost), whether I will change handlebars, indicators etc.

I've spent the last month disassembling the whole bike, so will write a few posts in chronological order up to the present.

The bike when I brought her home:
OGBikeCropped.jpg
 

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Discussion Starter · #2 ·
Proud of myself having removed the engine:
DSC_1016.jpg

The "lovely" engine:
DSC_1017.jpg

One seized piston, which I have since freed after soaking in penetrating oil and a wooden post:
DSC_1041.jpg

The other piston, still seized despite a month of soaking and some whacking..:
DSC_1043.jpg

I had to remove two of the bolts connecting the head to the crankcase because I couldn't get the rockers out and thus couldn't get the camshaft out. The points cover was also jammed on which meant force was needed to remove it, which caused one of the crankshaft tabs which hold the cam sprocket on to snap :mad: Very annoying but it was a clean break so when I get to the putting-it-back-together stage I'll see if it can perhaps be mended or if I'll need a whole new one.
 

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Discussion Starter · #3 ·
Giving the frame a wash at the coin-carwash:
DSC_1127.jpg

Haven't managed to get the generator off. Have screwed in the rear axle but it didn't budge. Might have to try and get my hands on a proper puller.
DSC_1270.jpg

Managed to get the oil filter cap off, but don't have the castle nut removal socket so haven't got that off either yet. Might try to make my own from a piece of metal or using welding wire as I have read on a few sites.
DSC_1271.jpg
 

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Discussion Starter · #4 ·
Managed to get the lower crankcase off so I could get to the guts while the generator and oil filter are still attached. Cogs seem to be in reasonable condition. This also means I have been able to flip the engine upside-down, and have filled the bottom of the piston with acetone/oil to try loosen the seized piston from the bottom.
DSC_1276.jpg

I've managed to get everything off the frame except for the rear guard. I undid the bolts on the left of the picture, and the large bolts that hold the rear rack/indicators in place were also removed. However, the guard was stuck fast. Maybe the guard has fused to the metal of the frame where they touch at those large bolt holes? Any advice for removal?
DSC_1278.jpg
 

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Discussion Starter · #5 ·
Seat pan was badly rusted out, so I am planning to try and make a copy from fibreglass.
DSC_1078.jpg

First step was patching up the holes with cardboard and covering the old pan in foil to create a smooth surface.
DSC_1096.jpg

Then I started on the Papier mâché. I think in total I did four coats (each of around two layers of paper strips, one horizontal and one vertical).
DSC_1102.jpg

Tada! This is the stage I am at so far. Next will be to cover this mould in cling wrap, then fibreglass. Once it's dry I'll remove it, trim the edges, and have a perfectly moulded seat pan. We'll see...
DSC_1198.jpg

N.B. While it may have been easier to fibreglass over the top of the old metal pan, I wasn't sure if this would be an exact mirror of its underneath side. Also, I wasn't very confident that it would stay in one piece if I removed it from the foam.
 

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Getting a rusty lump apart is hard. After that, all there is left is cleaning, polishing and painting. To help free the cylinders up get them as clean as possible. I'm pretty sure you are going to be looking at new pistons, rings and a rebore. I would use some oil, paper towel, Scotch Brite pads to mechanically clean the cylinders as much as possible. Odds are there is as much gunk between the pistons and cylinder wall and in the cylinder below the pistons. Some times it is necessary to pull the bottom case off and soak the pistons from below. One of the pistons looks like it is all the way down the bore to BDC. If that is the case, sometimes it is necessary drive the other piston down and let the cylinder rise off of the crank case. Then the other piston will pop up with the cylinder block. once it is raised the stuck piston can be driven down. Keep us posted.
 

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Seat pan was badly rusted out, so I am planning to try and make a copy from fibreglass.


First step was patching up the holes with cardboard and covering the old pan in foil to create a smooth surface.


Then I started on the Papier mâché. I think in total I did four coats (each of around two layers of paper strips, one horizontal and one vertical).


Tada! This is the stage I am at so far. Next will be to cover this mould in cling wrap, then fibreglass. Once it's dry I'll remove it, trim the edges, and have a perfectly moulded seat pan. We'll see...


N.B. While it may have been easier to fibreglass over the top of the old metal pan, I wasn't sure if this would be an exact mirror of its underneath side. Also, I wasn't very confident that it would stay in one piece if I removed it from the foam.
This is brilliant, I am watching with great interest!
 

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Discussion Starter · #8 ·
So that brings us to where I am today:

-Almost bare frame --> Rust to be sanded off, and then repainted.
-Engine in most pieces --> Need to free seized piston then I can finally have a proper look at it. I guess at least re-honed, maybe rebored.. Hopefully pistons are ok, but new rings I suppose? Once it is sorted, I will get started on rebuilding the bike.
-Engine pt II --> Also need to get the oil filter, clutch and generator off.
-Front wheel seems to roll well, rear wheel brake seized --> Haven't touched this yet.
-Electrics all taken off --> Need to clean the filth off the wires, then hook them all up and see if I get any success.
-Tank has rust inside but doesn't seem to leak --> I've had bad experience with a leaking fuel tank so am cautious about sanding and repainting the outside, but I think I'll look into this down the track. Any suggestions for cleaning the inside of the tank? I have read about filling it with petrol + bolts etc. and shaking?
-Seat --> Create fibreglass pan and if successful maybe also a second one. Then I can recreate the stock seat, plus design my own.
-Probably lots more I have forgotten/am naive about --> I'll stay optimistic :)

I will endeavour to keep this log updated and look forward to any advice or suggestions from the community. I have already found a lot of useful information in various threads on this forum which I've put to good use. Thanks!
 

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Even if you are on a budget, I suggest you have those cylinders bored and get new pistons and rings. Or buy used cylinders and pistons, hone them and use new rings, and sell these seized ones for someone to rebore...

Also, inspect the crankshaft. Hopefully, hitting the pistons did not ruin any crank bearings...

If you go through the trouble of rebuilding the engine, it's better to do it well, even if you are on a budget...
 

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Discussion Starter · #10 ·
Even if you are on a budget, I suggest you have those cylinders bored and get new pistons and rings. Or buy used cylinders and pistons, hone them and use new rings, and sell these seized ones for someone to rebore...

Also, inspect the crankshaft. Hopefully, hitting the pistons did not ruin any crank bearings...

If you go through the trouble of rebuilding the engine, it's better to do it well, even if you are on a budget...
Thanks for the advice. I will definitely be making sure to do it well, just hoping it won't cost too much in the end ;)

In regards to buying used cylinders and pistons, and selling mine, are you referring to the steel sleeve inbetween the pistons and the block as the cylinder? Or that entire section of the block? If it's just the sleeve, how would one remove that from the block? And if not, is it possible to remove the conrods (while everything is still together) from the crankshaft and thus take the stuck piston and block out as one piece?

Thanks again in advance.
 

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You can also remove the sleeves, but that is not very common for motorcycles - boring them to oversize pistons is cheaper after all. I meant the whole cylinder assembly, the cast alloy part including the sleeves.

I believe your model has a roller bearing crank that needs to be disassembled on a press. So, most likely you cannot easily remove the rods, unless they are bolted together.


I am sad to say you may have an expensive project. Pistons sometimes get stuck so much that you have to somehow drill\machine them out, to avoid ruining other things (like the crank)
 

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I've had a couple of CB175 engines with seized pistons, caused by standing and exposure to the elements.

First one came out by tapping on a wooden drift. Second one was stuck worse, a 51mm hole saw in a cordless drill sorted that one out.

ngin21.JPG

ngin22.JPG

This destroyed the piston, and gouged the cylinder wall, but it rescued a good crankshaft.
 

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Discussion Starter · #13 ·
First one came out by tapping on a wooden drift. Second one was stuck worse, a 51mm hole saw in a cordless drill sorted that one out.
This destroyed the piston, and gouged the cylinder wall, but it rescued a good crankshaft.
I will try to keep this as a last resort, but I am glad to know the technique if I am unable to remove it non-destructively.
 
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