Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Reborn 400 on October 31, 2026, 11:29:43 AM
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Inside the mounting area/crankcase boss, where the oil filter housing sits, I noticed this plug, which seems to be glued in and sealed with some kind of hard resin, above the top of the mounting thread(photo looking down from above).
Is this normal? Are they all like this?
I'm assuming it's original/factory procedure, but can't remember noticing it when I last owned one of these.
Any ideas guys and girls?
Thanks,
Johny
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I don't recall seeing anything like that when I changed the oil recently. It's possible that I just don't remember it but it looks very sloppy for OEM Honda and I think I would have noticed/remembered it. But I'm sure folks with a lot more experience with these engines will shortly advise as to whether it is normal or not...
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Well this image I've scalped out of the manual shows there is something there, but as said by Mike it looks like things are not very OEM, or someone has been awful ham fisted!
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I thought it was from the production engineering, that to machine out the exit oil gallery going down front of lower case to reach the main crossways distribution to crankshaft journals. That route looks to be cast partially blind with no logical access apart from that "port" in there for milling tool access. Subsequently blocked off at that entrance.
It looks like they first drill that blind countersink directly behind it, to then allow competent approach of milling tool on a flatish landing site in facilitating that machining operating.
Could be wrong, but that's from memory of the layout there when working on them.
Edit:- some images here on cases for sale
https://www.ebay.co.uk/itm/147634261333?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338454679&toolid=20006&customid=CjwKCAjwo5bXBhAEEiwAkgpgXNJg1kVk-Fs4GW6EyBvKr6qw_LcczA9ZOTvIUW-3duAF-SNaZL-5VRoCLWEQAvD_BwE%7Cnull%7Cnull&gclid=CjwKCAjwo5bXBhAEEiwAkgpgXNJg1kVk-Fs4GW6EyBvKr6qw_LcczA9ZOTvIUW-3duAF-SNaZL-5VRoCLWEQAvD_BwE&gbraid=0AAAAACmIvu09z0LzRpjOJbwq5gpUOvNGc&wbraid={wbraid}&loc_interest_ms=&loc_physical_ms=9217597&adtype=pla&gad_source=1&gad_campaignid=23873197324&gbraid=0AAAAACmIvu09z0LzRpjOJbwq5gpUOvNGc
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Pretty sure my 400 had something similar, that brown staining was also on a few places inside the engine casing, can't remember where as it was a few years ago.
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I don't recall seeing anything like that when I changed the oil recently. It's possible that I just don't remember it but it looks very sloppy for OEM Honda and I think I would have noticed/remembered it. But I'm sure folks with a lot more experience with these engines will shortly advise as to whether it is normal or not...
Thanks Mike, yes I thought it looked pretty sloppy too.
Johny
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Well this image I've scalped out of the manual shows there is something there, but as said by Mike it looks like things are not very OEM, or someone has been awful ham fisted!
Thanks for posting that Drawing, looks like it is meant to have something in there.
Johny
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I thought it was from the production engineering, that to machine out the exit oil gallery going down front of lower case to reach the main crossways distribution to crankshaft journals. That route looks to be cast partially blind with no logical access apart from that "port" in there for milling tool access. Subsequently blocked off at that entrance.
It looks like they first drill that blind countersink directly behind it, to then allow competent approach of milling tool on a flatish landing site in facilitating that machining operating.
Could be wrong, but that's from memory of the layout there when working on them.
Edit:- some images here on cases for sale
https://www.ebay.co.uk/itm/147634261333?mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338454679&toolid=20006&customid=CjwKCAjwo5bXBhAEEiwAkgpgXNJg1kVk-Fs4GW6EyBvKr6qw_LcczA9ZOTvIUW-3duAF-SNaZL-5VRoCLWEQAvD_BwE%7Cnull%7Cnull&gclid=CjwKCAjwo5bXBhAEEiwAkgpgXNJg1kVk-Fs4GW6EyBvKr6qw_LcczA9ZOTvIUW-3duAF-SNaZL-5VRoCLWEQAvD_BwE&gbraid=0AAAAACmIvu09z0LzRpjOJbwq5gpUOvNGc&wbraid={wbraid}&loc_interest_ms=&loc_physical_ms=9217597&adtype=pla&gad_source=1&gad_campaignid=23873197324&gbraid=0AAAAACmIvu09z0LzRpjOJbwq5gpUOvNGc
Yes, that makes sense, with the blind countersink behind it.
Thank you,
Johny
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Pretty sure my 400 had something similar, that brown staining was also on a few places inside the engine casing, can't remember where as it was a few years ago.
Hi Ted, thank you...Put my mind at ease a bit now!
Johny
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Similar on 500 as well, i always took it to be a machined gallery blank
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Thank you Bryan, so it's normal but messy. When you look up inside the threaded boss, you can clearly see the machined oilway running down at an angle.
Thanks everyone for your comments.
Johny
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They say that confession is good for the soul, so, after voicing my criticisms about AI (usually connected with photography), I typed the query into Google and the attached was the response. Quite informative.
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But that’s just regurgitating stuff from enthusiasts’ sites (including this one).
Sent from my iPhone using Tapatalk
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Ye, clever search reach/recovery, but you still need to be able to judge if true or not.
By illustration:- the resistance against pressure clearly wrong. They've (Honda engineers) done something clever with the siting of that acces/plug as it's effectively pressure neutral in that location.
Positioned inside the oil filter housing, it has the pressure equal to the supply line it's plugging. The resistance that makes the pressure is downstream of this point (bearing clearance etc) causes the whole system from pump output to those bearing exits to be the same.
That's how I see it anyway.