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This Can't be Good...

Boxbike

Well-known Member
Joined
Aug 23, 2021
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Location
Flushing, Michigan
Came across this after removing headlight bucket bracket. Looks like cracks in the top piece of the forks. Pictures of both sides. I'm assuming I'll need a new top piece...???



Also, found that one of the three alternator cover screws seems to be striped out or not long enough to thread in. All 3 screws are the same length when removed. The picture show's the screws pushed into the start of the threads. But one screw pushes in all the way in without touching any threads. Do I need a longer screw or is there an insert or something that is missing?
 

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Some have gotten their top bridges welded, depends on the shop you take it to whether they'll do it or have the skill to do it. Otherwise you'll need to find a good used one, might be a challenge since many of them get broken by ham-fisted POs. As for the alternator cover screw hole, I believe the threads for those screws are in the aluminum of the cover, tabs inside that the screws thread into after going through holes in the stator. Seems the aluminum is stripped. I suppose you could helicoil it but picking up a used cover would probably be the best way.

honda-cb350k2-super-sport-1970-usa-left-crankcase-cover-rearcover_bighu0028e4010_91b2.jpg
 
Replace the cover. There's not enough material for a Time Sert and a Heli Coil will only work for a short time before coming out. This is a frequently removed bolt so Time Sert would be the only viable long term repair.
 
Shucks. I doubt that was the project start you were hoping for, but glad there’s fixes available for both.


Tom - 1982 CM450E / Midwest USA
 
Thanks guys for your thoughts. The bike came with an extra engine so I'll check the cover on that one and who knows, might get lucky. I'll tackle the top bridge once I get to working on the front end which I figure will be in step #176 in my process. Regardless, I'm enjoying working on the bike and learning new things. Cheers.
 
Just a comment on the Top Bridge.
I could be wrong but from the pictures I do NOT SEE the "D" Shaped Spacers that go in the Slot to prevent exactly the problem you have with the cracks.
They "LOOK" at lot like basic Washers with one side cut off to make them "D" Shaped - The "D" Shape allows them to not contact the Fork Tube.
BUT... They are much Thicker then any standard washer you will find.

Even with the spacers it is possible to crack the Top Triple Tree - but it is harder and not as frequent.

I think it is Common Motor who has a machined replacement but FYI - Not Cheap,
But since it is a NLA Part it is either - Used (real hard to find not cracked) - or costly new replacement.
 
Thanks Yendor for the info on the D Shaped Spacers. Spoke with my local small cycle shop and he believes he has a used top plate in his inventory. Hopefully he'll find it and I'll be sure to get the spacers along with it.

In regards to the issue I had with the alternator screw hole, the problem ended up being that the 'ear' inside the main cover had snapped off so there was nothing to screw into. The piece was still inside, so I held it in place as I screwed the small cover onto the main cover, then attached the main cover to the engine side. It should hold until the small cover gets unscrewed from the main. Not a permanent fix but good till I source out a replacement main cover.
 
Ok fellas, I was really hoping I could find this out on my own but I can't, so I'll have to ask...
After having been told a few times now that I should have D Shaped Spacers on my top plate which would have helped stopped the cracks from occurring at the fork holes, I have yet to find any information about them in other posts or better yet a picture of them. Maybe I'm not understanding their function or something but can someone explain and show? Thanks.
 
Replace the cover. There's not enough material for a Time Sert and a Heli Coil will only work for a short time before coming out. This is a frequently removed bolt so Time Sert would be the only viable long term repair.
Or, run a 1/4"X20 tap in the holes and pick up some 1/4 X 20 oval head screws at the hardware store.
 
Ok fellas, I was really hoping I could find this out on my own but I can't, so I'll have to ask...
After having been told a few times now that I should have D Shaped Spacers on my top plate which would have helped stopped the cracks from occurring at the fork holes, I have yet to find any information about them in other posts or better yet a picture of them. Maybe I'm not understanding their function or something but can someone explain and show? Thanks.


Here's a pic of the "D" spacer. It's function is to prevent over "clamping" of the fork tube and causing it to crack.
D-spacer1.jpg

The flat part of the spacer would be against the fork tube.
D-spacer2.jpg
 
When I looked at the pictures of his top bridge, it seemed like the broken pieces had the taper of the V-shaped space the CB350G top bridge came with IIRC, the one like the CB360 where they no longer used the D-shaped washers. Could just be the angle of the picture, but it's obviously a later model front end on his '69 CB350.
 
Or, run a 1/4"X20 tap in the holes and pick up some 1/4 X 20 oval head screws at the hardware store.

I think just earlier he mentioned when he took the larger cover off the entire threaded tab had broken off the inside of the cover where the small cover screw threaded into.
 
Many thanks boddy for the pics of the D spacer. I get it now.
When I posted my introduction post with pictures of my bike, someone else noticed a lack of the D spacer, with another suggesting that my forks did not appear to be original to the bike.
Thanks everyone for the help. Next wks project will be attempting to get the motor to turn over. Have some prep work prior to the first kick but I'll report back with results.
 
The washers only came on the CB350, CB360's had a major issue with top yoke cracking if overtightened. (I bought 4 CB360's, 3 had broken yokes)
CB350/400 four will fit as will later CB250/360 or 1974 CB350
The four cylinder ones are different for instrument mounts though but even so will be far better than a broken yoke.
Oh, Helicoils.
Never had a problem with them when correctly fitted.
The reason they 'come loose' is the hole wasn't drilled or tapped properly then some idiot tried threadlock to hold them in.... (even heard some instructors recommending thread lock on Helicoils.when I was at MMI :rolleyes: )
There can be a problem if you fit stainless steel screws as stainless tends to bind on stainless.
I use plumbers Teflon thread paster which seems to 'cure' the 'problem' and work better than anti seize
 
In reference to post #6 from Yendor,,,
I've searched for the D shaped spacers for my new top plate but can't find them being sold anywhere. I figured I could make my own but apparently they are thicker than a regular washer. Don't know if it would make a difference so I thought I'd ask. Does anyone know how thick they should be?

 
Someone here should be able to measure them for you, but I believe they are hardened steel so they don't crush. You can find them on eBay sometimes but they'll be expensive
 
I have measured them in the past but it was at least 15 years ago.
I'm almost certain they are 2mm thick.
If you can find 1mm thick washers, just superglue two together and file a flat.
If I remember right, the clamp only needs to close about 0.5mm
If anyone has an accurate measurement of thickness it wouldn't be a problem to just turn up a few in stainless steel, I still have a short piece of stainless bar
 
Thanks fella's for your responses. I just checked eBay and found a pair, and you're right, they weren't cheap but still much less than another usable top plate. I can check another 'need to' off my list.
 
I have measured them in the past but it was at least 15 years ago.
I'm almost certain they are 2mm thick.
If you can find 1mm thick washers, just superglue two together and file a flat.
If I remember right, the clamp only needs to close about 0.5mm
If anyone has an accurate measurement of thickness it wouldn't be a problem to just turn up a few in stainless steel, I still have a short piece of stainless bar


The D washers on a cb450 are 2.3mm thick and the gap in the top plate is 2.7mm. Not sure if the 350 is the same.
 
Thanks for the measurement.
I'll check 360 and see what that is, knowing you need around 0.4mm 'crush' should be very handy
Probably make some for 360 as I know good top yokes are getting real hard to find (I'm fitting Suzuki forks to two of mine, easier than finding new top yokes)
I have almost all the parts to build a reasonable looking stock bike
I got Katana 600 forks real cheap as no one wanted them 10+ years ago (and probably less people want them today :rolleyes:) was given a set of 2004 GSX-R forks for doing some machine work (blue, celebrating 20 years of GSX-R)
 
My top yoke is cracked too. I found a reasonable one on ebay & have cleaned it up & painted it. How hard is it to replace those? Looks like there are several things that have to be removed to get it out of there. Anything to watch for when doing this?
 
My top yoke is cracked too. I found a reasonable one on ebay & have cleaned it up & painted it. How hard is it to replace those? Looks like there are several things that have to be removed to get it out of there. Anything to watch for when doing this?

Not too terrible a job, just requires removing the handlebar mounts and gauge bracket from the top bridge.
 
Great Thanks!!! I might tackle this while we have rain over the next several days.

If you need to post about the process again, please start a new thread for the replacement since this is another member's thread for finding a replacement and new D washers (which hopefully you have if yours requires them)
 
I've got two cracked ones. I want to find a TIG guy around here. I know folks have repaired these before with success. I've got some damaged cases too. The way prices for good used parts keep climbing and some things are just MIA on ebay anyway, it makes sense to save this old stuff. It's satisfying and educational for me.

I wonder what an adequate TIG set up costs and how hard is it to learn.
 
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