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CT-175 Engine Rebuild Check Point Please

  • landyr67g
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CT-175 Engine Rebuild Check Point Please was created by landyr67g

Hello, Just asking for a sanity check with the slow motion rebuilding a 1970 CT175 engine.  Rebore and new cylinder, New con rod, crank journal rust welded, and then resized.  Balanced with the piston.  Japanese case bearings and seals.  For the re-assy, I put the gears/shift drum into the LH case, then pulled the crank into position (with shim).  But I did have a problem.  With the crank puller tool, I could not get enough force to draw the crank into the LH case.  I simply could not stabilize the tool while cranking the tool's big nut.  So I pulled it out and froze the crank and preheated the case out in the hot sun on 90F day.  This time it creakily drew into the case to a definite hard stop.  I think all is good except I am surprised how stiff the crank turns and dreaming at night if the journal is slightly oversized and is stressing the bearing ID.  Also when I spin the crank in the LH side, there is bearing noise amplifed by the case....not crunchy or rough but just noise.  Is that normal?  It is oiled, and I thought it would be more silent and more free spinning.  I do have a double seal on the LH case if that is relevant.
Thanks for any comments.
Joe M 
18 Sep 2022 22:05 #1

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Replied by Tinkicker on topic CT-175 Engine Rebuild Check Point Please

1.  No new bearing is ever completely silent.  You can expect some noise.  Of course that noise is subjective and even a recording will tell us nothing.

2. Again, how stiff is a new crank.  Where to start? Subjective again.  As a guide, if you spin it and the rod is above the case and not catching it, I would expect it to rotate at least twice after giving a good hand spin.

3.  In 12 years as a motorcycle tech, I never once used any sort of puller to pull the crank into the gen side case.  I heated the case till when spitting on the case makes the spit go into a little "ball" (around 120C) and not just sit flat boiling away.  I then just dropped the crank straight in under its own weight.  Pulling it in at room temperature can cause galling, mishapen bearing locations, bruised bearing tracks and even cracked cases if you get it badly wrong.
I trust you lubricated the bearing location and the outside of the bearing before you started pulling?
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Last edit: 19 Sep 2022 01:00 by Tinkicker.
19 Sep 2022 00:44 #2

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Replied by RT325 on topic CT-175 Engine Rebuild Check Point Please

Just my thoughts but the left bearing should be super tight on the shaft & tight in the case so really needs an extra clearance bearing on the left like C3 or C4 That's talking ball clearance, not fit in the case or on the shaft but ball extra clearance overcomes the expanding & squashing by shaft & case. Right side is different as the shot is a zero clearance sliding fit on the shaft & held tight by the crank nut & gear. I've only been working on them for 60 years but can't remember yesterday. Call my wife darling incase I get the name wrong lol. Actually I have an AT1 magneto model like your CT1 not electric start like US 125's but have a 175 top end on mine. Without reading back & loosing where I'm typing I think you said you had the crankpin holes filled & machined. Blimey that's getting radical, or did I misinterpret & it was the left crank shaft as they can sometimes spin on the shaft then wear it down so a new bearing is still loose when right home on the shaft. Hense building up the shaft. If 'that's' what you meant then has it been machined just fraction of a fraction too tight for the bearing so once in the case & squashed from outside its causing tight revolving as I think you said. I'll leave it the--my baked beans are getting cold haha. Sorry about the damn long winded essay about not much.
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19 Sep 2022 01:07 #3

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Replied by MarkT on topic CT-175 Engine Rebuild Check Point Please

Was it the LH crank journal you had welded and resized?  Could it be a bit oversize?

As RT325 said, does the new LH main bearing have C3 internal clearance? 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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19 Sep 2022 05:54 #4

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Replied by landyr67g on topic CT-175 Engine Rebuild Check Point Please

Hello Again - The crank was previously rusted at the LH seal journal when I bought the cycle. [supect it was powerwashed then put away wet]. Anyway it's very difficult to find a crank that's not rusted, so I sent mine to crankworks.com where they are known for doing repairs. They took it apart, ground out the divot, welded, then resized the entire seal, AND bearing journal. They put it back together with new rod, aligned/tack welded the rod pin to crank webs as extra insurance, then balanced everything. It was alot of work but ok with that...although I do wish I had mic'd and measured before and after....
Regarding current fit, crank will not continue rotating after I flick the RH spline side between thumb and fingers (while keeping the rod free). Only other factor is that I greased the bearing in moly (didn't force "pack" it, just rubbed on one side working it in) and I have a LH double seal. Don't know if those are enough to conspire against but I can imagine how it won't spin like a top - as the loose bearing did lightly oiled out of the bag. The bearing is standard "partzilla" made in Japan...and only noted its basic sizing on its face. This morning I tried drenching the bearing through the crank and down the case lube hole with mineral spirits (paint thinner). Loosened up a bit but still not spinning free on its own. Myabe I'm worrying too much but at this point don't know if I should continue forward hoping its just the grease, or pull out the crank, measure the shaft, and compare to others. When I did both the failed and frozen stalls the journal and bearing ID were lubed.
19 Sep 2022 12:54 #5

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Replied by Pete-RT1 on topic CT-175 Engine Rebuild Check Point Please

I believe the mag side bearing is C4 clearance and clutch side is C3.
It should be marked on the bearing.
As RT325 explained this relates to internal clearance of the bearing ie. the play between the rings of the bearing, not the fit onto the shaft or into the crank case.
If you have a problem, which isn’t clear, it could be that the diameter of the crank at the bearing journal hasn’t been machined to the correct diameter.
Can you get a micrometer on the shaft to measure it.
I was lucky on my CT3, the seal area was rusted and pitted but the bearing area was ok so PJME in the UK machined the seal area only and I replaced the seal with a smaller one to suit.
Sorry, that’s not helpful to you right now.
 
Yamaha CT1-B
Yamaha CT1-C
Yamaha AT1-C
Yamaha DT175MX
19 Sep 2022 15:31 #6

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Replied by landyr67g on topic CT-175 Engine Rebuild Check Point Please

Still worrying about this, so I pushed the crank out from the LH case side using a splitter.  Not surprised that bearing remained attached.  Now it's free and soaked with greasy mineral spirits so it spins nicely, but noisy to me in a way I did not hear before.  Not sure if from expansion damage, but going to replace it (also will be able to read its markings after removal).  Now to remove the bearing, I spied RT325's BFH demo from last year, but will definitely freeze the crank and torch the bearing prior to either BFH or pulling.  Hoping to pull to avoid risking the rebuilt crank assy.
Regarding the resized bearing and oil seal journal, does anyone have an actual or published measurement for that diameter?  Curious what I got!  And regarding the cranks stiffness, still wonding if from damage or from the double seal...or both.
Joe M
20 Sep 2022 21:06 #7

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Replied by Ht1kid on topic CT-175 Engine Rebuild Check Point Please

What kind of oil seal did you use?
20 Sep 2022 21:40 #8

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Replied by RT325 on topic CT-175 Engine Rebuild Check Point Please

Don't quote me but the bearing is a 6205 so 25mm id & 25mm crank size i guess--if that makes it tight fit, or does crank need to be a half thou bigger or something. The right side by memory is a 6304 & that is a hand slide fit on the shaft so maybe the right side is a gnats whisker under the bearing std size on purpose for a slide fit--held tight by the crank nut on that side.
Anyway--i just google & came up with this link. Too much for me to take in but are talking about a 6205 as it happens. Got halfway down the page & fell asleep haha.
www.darbarcompany.com/darbarcompanyblog/bearingfitclearance
21 Sep 2022 01:35 #9

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Replied by landyr67g on topic CT-175 Engine Rebuild Check Point Please

That is a great read...somewhat scary, though!
Although I haven't got the bearing off the stub yet, I measured the exposed journal just adjacent to the bearing and I get approx 24.99 - 25.00 using my digital calipers and pressing together the jaws them selves.  So guessing at this point the entire journal dia is correct.  So maybe the bearing slightly undersized (can't read and measure it yet) or are people comparing assembly fit using "used" cranks while this one is resized to "new"?  Don't know, but definitely going to swap the bearing and maybe the seal.  So its pn is "DC 25 40 8" with a "2" 180 degree away.  This is a double lip/spring seal.  Maybe overkill for LH case?
Regards,
Joe M
21 Sep 2022 20:19 #10

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