1971 CB175 Top-end Rebuild
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Thread: 1971 CB175 Top-end Rebuild

  1. #1
    Member DC175's Avatar
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    1971 CB175 Top-end Rebuild

    Hello, I haven't been on here a while because my CB175 has been working decently well. Now that it's getting cold, I won't be riding so often and figured it would be a good time to replace hopefully just the rings, but maybe have to get some +1 pistons and rings.

    The bike has over 20k miles, and compression is low in both of the cylinders. Last time I checked they were around 140/120 I believe. I haven't done the spoonful of oil test but will definitely do that before the tear-down to diagnose if it's another issue.

    Being moderately young and not having a mechanically inclined family, the tools I have on hand are extremely limited. Right now I have a socket wrench and set, a bunch of bits, pliers, a couple other wrenches, a micrometer, compression gauge but that's about it. For a top end rebuild, I believe I'll have to buy at least a hand impact driver and torque wrench. From what I've read on this site, I would also need a valve spring tool but figure I will just go to the shop to get those installed. I also plan to remove and clean the clutch plates as even after adjusting the clutch cable multiple time, with the clutch dis-engaged (lever pulled in), the back wheel will still spin a bit.

    Are there any other tools needed?

    Whenever I do this, I plan to document it fairly well as I can't seem to find a good source for the CB175 top-end rebuild.

  2. #2
    Senior Member Simo's Avatar
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    Re: 1971 CB175 Top-end Rebuild

    Hi
    You'll also need a hammer ( for the impact driver) a manual ( download and print ) a camera and a pad and pen to document as you go
    Zip lock bags to put parts in and a marker so you know what they are
    Blood, Sweat, & Gears
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    sales supporting 66Sprint's 2016 LSR Build

    http://www.hondatwins.net/forums/22-...d-attempt.html

  3. #3
    Member DC175's Avatar
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    Actually got around to taking out the engine. Took off the valve cover, head, cylinder and did an acetone test. Right intake looked like it was leaking so I plan to remove the valves, lap then and re-install. I'd like to confirm a couple things before I do, probably considered common sense to some but sadly not me:

    1. To remove the valves/valve springs, I don't need to remove the points and tach housings on the left and right side of the engine correct?
    2. I plan to remove the valves, clean the combustion chamber with some simple green purple and a blue non-scratch sponge or nylon brush, any worries there?
    3. With the cylinder off, I'm going to get it measured from a local shop to make sure it's still within spec. I plan to clean it with simple green purple prior to getting it measured, will the cylinder rust if I use water/simple green purple?
    4. Best way to remove stuck on gasket material? Currently using a metal putty knife, I'm assuming goo-gone may work?

    Thanks for the help. I'm hoping to get this up and running well during the winter to fully enjoy next year.

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  5. #4
    Member magconpres's Avatar
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    1. To remove the valves/valve springs, I don't need to remove the points and tach housings on the left and right side of the engine correct?
    2. I plan to remove the valves, clean the combustion chamber with some simple green purple and a blue non-scratch sponge or nylon brush, any worries there?
    3. With the cylinder off, I'm going to get it measured from a local shop to make sure it's still within spec. I plan to clean it with simple green purple prior to getting it measured, will the cylinder rust if I use water/simple green purple?
    4. Best way to remove stuck on gasket material? Currently using a metal putty knife, I'm assuming goo-gone may work?
    1) You probably need to remove the points and tach housings to get the rocker arms out. Even if you don't, you probably should. It will make the rest of the work easier and they aren't hard to remove. Plus , they will be safe on your shelf while you work on the head.
    2) I don't think there is any risk of cleaning as you describe, but am not sure that's going to cut it. Depends on how much carbon build up you have. You may need to soak the chambers with something stronger, which may be tricky if the valves leak.
    3) if you're going this far, assuming the bore is in spec, I'd put in a new ste of rings and have the shop hone the cylinder for you. If you wash them, which you should do after the hone anyway (I use sudsy dish soap at this stage), just wipe the cylinders down with a paper towel dipped in motor oil after you dry them well.
    4) Patience and gasket remover work well. Gasket remover also removes patient, etc. I try to avoid using it and just use a gasket scraper or a fine fiber disk on a grinder. Goo gone may work...never tried it.

  6. #5
    Senior Member Bill H's Avatar
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    Cleaning the cylinders I use Dawn dish washing soap . They will flash rust in just a few seconds so I clean them with paper towels and wd40. Keep doing it till the towels come out clean.
    Make this the last thing you do then cover it till you are ready to reinstall it.

    Bill

  7. #6
    Member DC175's Avatar
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    Thanks for all the replies guys. To provide an update here what I did over the past few weeks:

    1. I ended up not removing the valve springs/rocker arms and lapped the valves only after removing the valve retainers. I'm 100% sure this is not advised but I lapped the valves and re-leak tested and it seemed to hold up. Obviously I made sure to not have any lapping compound fall down, that'd be bad...
    2. Combustion chamber, and the valves, were pretty carboned up. I used seafoam to clean the combustion chambers decently well but definitely not perfectly clean. Did the same with the valves and also had some steel wool type dremel tips I used to clean them.
    3. One bore was ok, the other looked like it had sat for a while and rusted a little bit. I ended up getting the bores opened up +.25mm with new oversized pistons. They looks 1000% better and with new rings I should better compression.
    4. For removing the gaskets, patience was definitely needed but I figured getting most of it off and not leaving any big chunks, the surfaces would still seal.

    So with all that I just received a Charlie's Place electronic ignition and bolted it up. Next is to torque the nuts and set the valve clearances. Then back in the frame, once it gets above freezing.

    Thanks again for the help and recommendations.

  8. #7
    Junior Member Alex V.'s Avatar
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    Sounds like you're just ahead of me. After blowing the head gasket last summer I pulled my top end apart and found the tops of the pistons/combustion chambers dinged up and some scuffs on the skirts/walls - it didn't use any oil to speak of and ran fine beforehand, but compression was low. So I had just enough tolerance left to keep std. bore and clean it up with a hone, and am waiting on the piston & ring set (due in a couple weeks from Japan) to go back at it. Not touching the bottom end, just lapping the valves, de-carboning everything, and a new gasket set. I'll be curious to see how both our rebuilds work out.

  9. #8
    Junior Member mtn_'s Avatar
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    I'm doing a rebuild myself as well. Seems like you're on the right track. Very confused about your valve job, it is one thing to have them not quite leak but it's another to inspect your camshaft and rocker arms on such a high mileage bike. This could absolutely be a main source of performance loss and valve timing. Also, if any compound were to get into the valve guide, very easy to do, it would be ruined the first time it ran. I would definitely recommend doing the full head inspection if you are expecting good long-term results from the rebuild. Shame to spend the money on a bore, pistons, rings, hone to find it was a worn cam or rocker arm causing minimal valve lift. Obviously this won't affect your compression ratings; they were low and probably needed the bore.

    Your jugs have been bored, were they also honed crosshatched? Your new rings will need to seat before compression will rise to its max. Be sure to get the end gap just right, very important. Your piston shouldn't have .004" clearance anywhere in the cylinder. The ring end gaps are even smaller i believe.

    Just to check, when you slap the thing back together be sure to get the cam chain is in the correct position. O facing up on the cam with the generator timing mark on the T. There is a proper order to torquing the bolts, too. Valve clearance be sure to do at top dead center, also the T mark. Then I would say do the ignition timing while you're down there but I see you've gone the modded route. Hope this helps!
    mtn_

    1968 CL175 K0 project (long-term perfection)
    1969 CL175 K3 daily
    1970 CB175 K4 daily
    1972 CL175 K6 project (bore)
    1972 CB350 K4 project (frame)
    1969 CT70 K0 project (fuel/spark)

  10. #9
    Senior Member Richard_Pitman's Avatar
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    Agreed. Not removing the cam and rocker arms is at odds with the FSM procedure, and must have made life very difficult for valve removal.
    1972 Honda CL175

    1999 Honda CB600 Hornet

  11. #10
    Member DC175's Avatar
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    Thanks again for the help guys. And I completely agree that I should have fully disassembled the head. Due to lack of tools, time, and a insufficient workspace, aka my studio living room, I decided I would take the chance. I finally got around to re-torquing the crown nuts in the order my Clymer's manual said to. Then I adjusted the valve clearance for each one at TDC on the compression stroke. I received the charlie's ignition and got it mounted. This Sunday I hope to put the engine back in the frame, connect electricals and time out the electronic ignition.

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