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Discussion Starter · #1 ·
I don't think I'm an idiot but sometimes I feel that way.

I got my new fork seals in today so I started the fork rebuild. The forks came apart pretty easily (other than that big snap ring clip being tough to remove with a small set of snap ring pliers). Rather than just change the fluid and the seal I thought I'd measure a few things like the manual says to do to ensure things were within spec and looking good. I used some calipers to measure the piston dia. and it came out a little bit above the min. spec at 1.558 (min is 1.551).

I have a dial bore gage but it's to large (minimum is 2") to get inside the bottom case. I've a set of inside mics but they are much too short and I would only be able to measure the case at the top by the seal. I'm guessing that the bottom of the case (lower leg) is probably larger than the top since that's where the wear (if any) takes place.

Does someone have a technique for measuring the bottom of the bore?

Now for my "I'm really not a moron" question. After I used my calipers to measure the piston I remembered I had a metric mic stashed away that had never been used (in a previous life it was SAE only).

Can someone take a look at the following pictures and tell me what the mic is reading? The scale on the outside of the mic says it's range is 25-50mm. The 1.551 min dia. measurement for the piston works out to 39.4mm. In my mind that mic is reading about 26.77 mm. Am I missing something here? And, in case you're wondering, those are not my hands. :)

Disassembled left fork. I didn't see any reason to remove the circlips. Is there a reason I should? I've already run the parts through the solvent tank and used stripper on the fork lower. I sure wish people wouldn't take sandpaper to the fork legs. It really tears them up and makes restoration that much more difficult.



Here is the measurement of the piston using calipers.



Here is the same piston being measured by the metric mic.



And last but not least, the manual calls for about 225cc of 10-30 motor oil. Does anyone have any experience using something else? Additionally, I've always found it difficult to accurately measure the amount of fork oil to fill a beaker and, as such, I have a cool little tool that we use on the race bikes to suck out the oil to a predetermined 'oil level height" in the tube. Is there a call-out for measuring the fork oil in this manner?

Thanks
 

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Does look like that mike is reading about 26.27 mm to me.
Does it zero out ok?? Assuming you can find something that's exactly 25 mm??

As for the fluid, I always just use fork oil, personally.
I hate ATF on general principles, and I figure motor oil goes in your motor.
So I use fork oil - on those clunkers I might try 15 weight to start out and go from there.
 

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Discussion Starter · #3 ·
tbpmusic said:
Does look like that mike is reading about 26.27 mm to me.
Does it zero out ok?? Assuming you can find something that's exactly 25 mm??
Good question and I just happen to have a 25mm standard so I went out to verify the mic accuracy. It looks like it right on. I then got to thinking that maybe the manual might be in error so I converted 1.551 to mm and it comes up to 39.395, so that's not the problem.

I'm sure the dia of the piston is ok but it's irritating that I can not figure out why I'm not reading the mic correctly.

Thanks for looking Bill. I'll give the 15 wt. fork oil a try.
 

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Discussion Starter · #5 ·
NE350 said:
Mike,

I have had success measuring fork oil with..... a baby's bottle. Yup! It has milimeters nicely marked on the outside of the clear bottle

Matt
Thanks Matt, but I'm the only baby in this household. :)

Actually, I've got a nice beaker designed for measuring fork oil but after I spill a little and leave a little in the beaker we've always found it easier and more accurate to suck it out to a predetermined level.

Now, with that said, if it was a good enough way for the mechanics to do it back then, then it's probably more than good enough more garage hack effort.
 

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Mike -

Are you sure those are K4 forks??
Looks like they might be K5 forks to me, but I could be wrong. What's the VIN number of the bike?? Are the forks original to the bike??
And K5 forks only need 155-165 cc of fluid, according to the Honda manual.

Another observation would be that the manual's specs (page 74 of my manual) are probably for the older external spring forks (K1-K2). I can't find any specs for the newer type forks.

Also, though it's tough to see in the photo, but it looks like your vernier calipers are actually reading about 1.057" (assuming that bottom scale is tenths of an inch, and isn't that top scale in mm??) - that converts to 26.847mm, which is closer to what the mike is reading. I think in most cases, I'd probably trust the mike a little bit more.

Feel like reading that caliper again??
 

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Discussion Starter · #7 ·
tbpmusic said:
Mike -

Are you sure those are K4 forks??
Looks like they might be K5 forks to me, but I could be wrong. What's the VIN number of the bike?? Are the forks original to the bike??
And K5 forks only need 155-165 cc of fluid, according to the Honda manual.

Another observation would be that the manual's specs (page 74 of my manual) are probably for the older external spring forks (K1-K2). I can't find any specs for the newer type forks.

Also, though it's tough to see in the photo, but it looks like your vernier calipers are actually reading about 1.057" (assuming that bottom scale is tenths of an inch, and isn't that top scale in mm??) - that converts to 26.847mm, which is closer to what the mike is reading. I think in most cases, I'd probably trust the mike a little bit more.

Feel like reading that caliper again??
Sure will.

Re: the year of the forks. I'm pretty sure the forks are original to this bike but then I suppose we can not be sure of anything that's almost 40 years old. The title and frame say the bike is a 1970 (10/70) but the VIN is CB45041C2773 and I think that is a K4.

Bingo, right you are on the caliper measurement Bill. I don't need to remeasure, I can see the caliper is reading 1.057 or so. Thanks for catching that. I was reading the book and the spec was 1.551 and my little pea brain saw something that wasn't there.

Now, the problem is what forks am I measuring?

Oppps, I need to get some sleep. I'm measuring the wrong piston. I was measuring the Aluminum piece that bolts inside the bottom of the fork leg. Thanks for asking the right questions. The actual measurement of the correct part is 39.44 so I'm good to go.

I'm such a Bozo.
 

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I don't mean to intrude, but have you thought about going digital with your measuring tools? I did, and I'll never look back. No brains required :lol:

GB :mrgreen:
 

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Looks to me like the mic is showing 26.77mm, there is a half mm mark showing, plus 0.27. (25mm+1mm+0.5m+0.27mm)
learn to read what you have, it helps keep your brain alive
If you want to convert from inches to mm, multiply by 25.4, mm to inch, 0.03937
PJ
 

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Discussion Starter · #10 ·
crazypj said:
Looks to me like the mic is showing 26.77mm, there is a half mm mark showing, plus 0.27. (25mm+1mm+0.5m+0.27mm)
learn to read what you have, it helps keep your brain alive

PJ
As I posted in the first message, I had the mic reading correct, it's a dial caliper I had a brain freeze on and those numbers didn't jive with the book because I was measuring the wrong part.

A little sleep and I should be all better now. :)

Bird76Mojo said:
I don't mean to intrude, but have you thought about going digital with your measuring tools? I did, and I'll never look back. No brains required :lol:

GB :mrgreen:
Yea, the digital stuff is nice but for as much as I need to measure (very little) it wouldn't make sense to convert. Besides, I enjoy having to thing about the measurement when I'm taking it.

Actually, I have a vernier caliper laying around here once that was given to me in the '60's by an old guy who wanted to encourage me in an engine rebuild I was doing. He showed me quickly how to read it and I recall it being pretty simple. I've kept it all these years but I doubt I could read it today although it's a very accurate tool.
 

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crazypj said:
Looks to me like the mic is showing 26.77mm, there is a half mm mark showing, plus 0.27. (25mm+1mm+0.5m+0.27mm)
PJ
Yeah, that might be right - hard to say, I can't tell what that first mark past 25 actually is without seeing more of the scale exposed.......
 

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I use a 50ml syringe with a bit of fine rubber tubing on the nozzle for fork oil. Suck it right up out of the bottle. It is very accurate and never spills a drop. Another is also handy for batytery electrolytic fluid.
 

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Discussion Starter · #13 ·
twinz said:
I use a 50ml syringe with a bit of fine rubber tubing on the nozzle for fork oil. Suck it right up out of the bottle. It is very accurate and never spills a drop. Another is also handy for batytery electrolytic fluid.
That's a good idea and worth a try. Thanks for the tip.
 

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I've read thru this post and am wondering if the K2- K3 used a different amount of fork oil than the K4- K7... it was suggested the K4 needs 15# at 155-165cc. Thanks for added info, danWI
 

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danWI said:
I've read thru this post and am wondering if the K2- K3 used a different amount of fork oil than the K4- K7... it was suggested the K4 needs 15# at 155-165cc. Thanks for added info, danWI
You find conflicting info on this -


Basically, CBK1-K2 had similar external-spring types.
Then K2/K3 had internal springs.
K5-K7 had a different internal-spring fork.

CL's (I think) were the same.

This from the Clymer manual -
Early 2-spring type 220-230cc (7.0-7.3 oz)
Early 1-spring type 285-295cc (9.0-10.0 oz)
K3/K4 - 220-230cc (7.0-7.3 oz)
K5-K7 - 135-145cc (4.6-4.9 oz)

This from the Honda manual -
K1-K2 285-295 cc
no mention of K3/K4
CB450K5 155-165cc (5.3-5.6oz)
CB450K6 135-145cc 14.6-4.9oz)
CB450K7 135-145cc 14.6-4.9 oz)
CL450K5 155-165cc (5.3-5.6o2)
CL450K6 155-165cc (5.3-5.6oz)
 

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I also need to take my weight into consideration too... i'll give 220cc (7.48oz) a try and go from there. thanks for your input Bill, danWI
 
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