Author Topic: My cb750k7 build (Read 5521 times)

InexperiencedAaron · « **on:** February 22, 2014, 02:28:13 PM »

My first build.
Lapped the valves, polished the gasket surfaces, steam cleaned the entire engine, honed the cylinders, replaced the piston rings and cleaned the pistons. All that is left is to put her back together, then I get to paint her

Here is a link to a little video I made of the progress so far.
Honda cb750 build

martin99 · « **Reply #1 on:** February 22, 2014, 03:44:59 PM »

You sure about those cylinders Aaron? If those pics were taken after honing I wouldn't be happy. Unless they're just bad pics there seems to be some worrying marks in there. Even the top ridge marks are still visible. I'd double check my measurements if I were you, check for ovality in the bores and ring gap. General rule, if you can catch your fingernail in the scratches they're too deep and honing may not be enough. I know it's exciting getting the engine back together, but best to take your time to get it right.

Rmart · « **Reply #2 on:** February 22, 2014, 07:42:41 PM »

I'm going to agree with oldskool the second photo shows a couple of places of concern I would try and find a bore gauge and mic your clyinders take readings at the top of the clyinder right where the ring travel stops,then mid clyinder and finally at the bottom of the clyinder where the ring travel stops. take a reading then turn the gauge 90 degrees in the same area and take another reading, this will tell you if the clyinder is out of round, and the 3 readings from top to bottom will tell you how much wear the bore has use a good micrometer to mic the bore gauge so you get accrued readings, if you you can run a finger nail up and down the bore and catch any rough area then you should bore it to the next oversize.
Don't be afraid to ask for help we're all here to help each other( and laugh) I bought my first CB750 in 1971 and I still have along with a 74,74 and a CT 70 and I stil learn new things.
Have fun with it
R

InexperiencedAaron · « **Reply #3 on:** February 22, 2014, 07:56:12 PM »

Thanks a lot guys!
Appreciate the advice.
I'll get a micrometer ASAP and check. It's going to be sad if I have to go the next size. Pistons aren't cheap and neither are the rings.
-Aaron

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InexperiencedAaron · « **Reply #4 on:** February 23, 2014, 04:04:33 PM »

So I took it down to my local motorcycle mechanic and he said it'll smoke but that's about all. Since I'm already over what I wanted to spend I'm just going to live with it till I get on my feet financially. I know that's the last thing any of you want to hear. Oh no he's going to half ass a restore but sorry guys. I'll do it right next time around

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calj737 · « **Reply #5 on:** February 23, 2014, 05:26:04 PM »

Is there no way to re-hone the cylinders without causing a re-bore? If it smokes, it's burning oil. That is bound to cause a motor failure when you forget to top it off. THEN you will be financially hurt much worse.

InexperiencedAaron · « **Reply #6 on:** February 23, 2014, 05:35:11 PM »

I have no idea. I'm going to take it to him when its an actual work day and ask him if there is anything he can do. Today was his day off so he didn't really want to deal with it. Haha

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MikeKato · « **Reply #7 on:** February 23, 2014, 06:05:57 PM »

Fun thread so far

If the guy says it's gonna smoke when he's done with it then tell him You're done with him. Someone around here will sell you a set of jugs cheaper than any of your other options.

GL!

InexperiencedAaron · « **Reply #8 on:** February 23, 2014, 06:46:07 PM »

How much for some jugs?
I did all the work myself, I just asked the guys if I did anything wrong.

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MikeKato · « **Reply #9 on:** February 23, 2014, 07:03:05 PM »

Quote from: InexperiencedAaron on February 23, 2014, 06:46:07 PM

How much for some jugs?
I did all the work myself, I just asked the guys if I did anything wrong.

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Ask for them on this board and see what pops up.
http://forums.sohc4.net/index.php?board=45.0

GL!
Mike

InexperiencedAaron · « **Reply #10 on:** February 24, 2014, 05:55:51 PM »

Thanks for the info!
Great bunch of people on here.

AintNoEasyWay · « **Reply #11 on:** February 26, 2014, 05:38:23 AM »

Sweet. I'm in the same situation, rebuilding my first, & it's a K7 too. Looking forward to seeing your progress man.

iron_worker · « **Reply #12 on:** February 26, 2014, 06:32:02 AM »

I believe what the guy may have been saying that if he honed out all the defects in the cylinder to make it smooth again then it will probably smoke because the bores will be too big relative to the pistons/rings. This is assuming you re-used the old pistons and rings.

IW

calj737 · « **Reply #13 on:** February 26, 2014, 06:47:43 AM »

That is a distinct possibility, but the post is very unclear.

Is it possible to "hone" a cylinder in a way that removes sufficient material to enlarge the bore? I've always interpreted honing a method of finishing a cylinder and boring as enlarging. Am I confused here? Or are these terms interchangeable?

InexperiencedAaron · « **Reply #14 on:** February 26, 2014, 11:47:06 AM »

When you hone a cylinder you're just trying to create a good cross hatch so the new piston rings will have a good surface to adhear to. Boring is what you do when you want bigger cylinders, or need bigger cylinders to discard any imperfections that may have been.
It's raining currently, so I probably won't have any progress up for another week or so. Sorry guys.

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edwardmorris · « **Reply #15 on:** February 26, 2014, 12:12:51 PM »

Quote from: calj737 on February 26, 2014, 06:47:43 AM

.....Is it possible to "hone" a cylinder in a way that removes sufficient material to enlarge the bore?...

I believe it is possible, done my crazy share of searching before I decided to go one size over. HondaMan/Mark has increased piston-cyl wall clearance by honing for extended periods, some good discussions in this thread

http://forums.sohc4.net/index.php?topic=68776.0

martin99 · « **Reply #16 on:** February 26, 2014, 12:21:45 PM »

If the cylinder is worn near to the outer limits of tolerance then it is indeed possible to remove too much material through honing. This is why honing is usually limited to three or four quick passes to achieve the desired cross hatch. The cross hatch retains oil in the bore during those vital initial revolutions of a freshly built motor to aid bedding in of newly-mated parts. Eventually as these parts bed in the cross-hatch is worn away, as are the surfaces of the rings to some extent. There has always been a debate around whether it is necessary to hone if a re-bore has not been done and old rings are being replaced.

The issue I have with the advice the OP's mechanic has given him is that it's just not very sensible, or professional IMO. If it smokes (it shouldn't if it didn't before and original parts are being replaced) then the 'mechanic' has a 'told you so' get out clause and takes the money. How much it smokes can only be a subjective guess. The only way to do this is to properly measure the bores to ascertain wear and make decisions based on what the results are. Makes you wonder what other half-arsed advice will be given next; 'the valve stem seals are forty years old but they look alright so don't change them? Worst that can happen is it might smoke?'

calj737 · « **Reply #17 on:** February 26, 2014, 12:47:55 PM »

I still wonder if the comment "it might smoke" was a reference to a lack of a properly honed finish, versus honing it too far that would create an over bore need.

Perhaps the OP can illuminate us and will update once the machinist verifies the conditions of his jugs.

InexperiencedAaron · « **Reply #18 on:** February 26, 2014, 01:39:35 PM »

I haven't gone back to the guy at the shop yet. He literally just looked at it in the light without measurements so I think he was saying it'll smoke a little because of the poor hone I did.
I'm not experienced in this at all. My friend(who is a mechanic) did the first cylinder so I could get an understanding of how to hone it, then I did the rest of them. Mine look nothing like the one he did. I've stopped doing stuff until I can get a hold of some sort of mechanic, before I screw the whole thing up and have to bore it 1 size over. Especially since I've already purchased the new rings and fitted them onto the pistons.

calj737 · « **Reply #19 on:** February 26, 2014, 02:27:14 PM »

That makes sense. Prudence is mother of financial shrewdness. Hope it can be honed to avoid new over bore as your new rings would then be moot.

martin99 · « **Reply #20 on:** February 26, 2014, 02:37:38 PM »

Yes, that makes a lot of sense. Whether or not a re-bore is necessary will not depend on how well you have honed your cylinders, rather it will depend upon what measurements you obtain from them. Without measuring you are taking a cross-fingered approach to the job rather than making informed decisions. You have jumped the gun a little by buying new rings. You may find the cylinders are in spec and in that case all you will need to do is hone properly and fit your new rings. However as I think you know you will not be able to use the rings you have bought if a re-bore is needed, you will need new oversize pistons and rings to suit. You're right, it can be an expensive business. If you are in any doubt regarding the next step, post your measurements on here and you will find impartial advice will be given freely. Here's hoping it goes well for you.

edwardmorris · « **Reply #21 on:** February 26, 2014, 02:51:20 PM »

Quote from: oldskoolnuts on February 26, 2014, 02:37:38 PM

Yes, that makes a lot of sense. Whether or not a re-bore is necessary will not depend on how well you have honed your cylinders, rather it will depend upon what measurements you obtain from them. Without measuring you are taking a cross-fingered approach to the job rather than making informed decisions. You have jumped the gun a little by buying new rings. You may find the cylinders are in spec and in that case all you will need to do is hone properly and fit your new rings. However as I think you know you will not be able to use the rings you have bought if a re-bore is needed, you will need new oversize pistons and rings to suit. You're right, it can be an expensive business. If you are in any doubt regarding the next step, post your measurements on here and you will find impartial advice will be given freely. Here's hoping it goes well for you.

+1

I measured mine using snap gauges (pix in my build thread) and felt that the numbers were too close to not go over. It cost me a fortune to get new pistons from yamiya, and I didn't know that another site (cb750supply or something like that) had MUCH cheaper replacements, but they were two sizes over. I'd have gone with those despite being two sizes over just because they cost less than half of what yamiya's do.

InexperiencedAaron · « **Reply #22 on:** February 27, 2014, 03:51:39 PM »

Hey if you guys could support my YouTube page as well that would be appreciated. I will have more videos up, some how to videos and Just general progress. Thanks
-Aaron

InexperiencedAaron · « **Reply #23 on:** March 04, 2014, 11:04:39 AM »

Sorry I don't have anything new for you guys yet. I've been really busy. Finally got a new job, I'm officially the contractor for bank owned home for my region! I'll have some new stuff up after I get paid. lots and lots of new parts for the bike! I'm so excited I thought I'd share with you all!

-Aaron

MikeKato · « **Reply #24 on:** March 04, 2014, 01:01:29 PM »

Great news Aaron! Congrats

News:

Author Topic: My cb750k7 build (Read 5521 times)