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Discussion Starter · #1 ·
Ok guys, I'm the type to figure things out on my own and do my research to solve the issue.

So, this all started with a new purchase, 81' CM400T. It needed some cosmetics, (2) tires and a battery along with timing chain adjustment. I proceeded to start the self adjust procedure for the timing chain but came to find out the threads on the bolt were stripped. Only fix was to break down and remove the head so I could remove the guide and bolt and replace it. In a rush and without local suppliers who stock gaskets for our bikes, I decided to seal the head gasket with silicone and hope for the best.

Bike started right up and ran awesome, short run and I was happy, until I saw the leak. So, thinking it had to be the head gasket I ordered one online and waited for it to show up. Once it arrived I stripped her down jugs and all and put her back together being careful not to miss anything. All back together as last time and soon as she fired up she started to leak again. Of course everything cleaned up this time I had a good idea where the oil was coming from but was unsure of the reason, thinking the worst, I figured crack in the jugs.

Lots of reading on here and going back through many of the old threads I could only find partial solutions. I had oil on the lower 2 fins on the jugs, coming from the center of the jugs. I saw several pictures on here of the bottom of the jugs and the little lines/slits that Honda added but nobody seems to have an explanation why. Looking more closely, the head bolts are also exposed on the jugs the same as they are on the head, I never stopped to look that closely at the jugs in the past to notice this. Giving this some extra thought, I was thinking of the head bolts and the ones I had did not have the rubber on them. Again, I came to the forum and looked for explanations why these bolts have the rubber, but all I seemed to find was that the rubber was to block water and dirt. This didn't seem adequate to me, so today I pulled the 2 head bolts and installed a pair pulled from a 450 that had the rubber, this fixed my oil leak problem.

So, the reason for the post is to help some others and clarify what hasn't been explicitly said regarding these 2 bolts.

1) Center 4 Head bolts are exposed to the outside both in the head and the jugs.
2) The ones on the right with the rubber are required to seal oil from the little lines at the base of the jugs
3) Oil from the top of the same 4 head bolts can show itself anywhere from the rockers to the base, makes finding the source difficult, so special attention is required at the rocker assembly. Use Hondabond (I used motoseal myself, nobody stocks Hondabond, Yamabond or the like) & make sure the copper washers are in place

If anyone disagrees with anything I have said, please let me know, but I feel I am correct in my statements. Also, I believe from what I have read and my own understanding of the designs, a set of jugs from an earlier 400 without the lines may be swapped to the newer base and then using the head bolts without the rubber should work fine. I also read people suggested using JB weld and filling the lines which I would think is the only option on a 450.

Here are some pics I shot for reference:
20180701_091516.jpg
Top of Jugs
20180701_091528.jpg
Bottom of Jugs, Note the (2) lines on the edge of the holes
20180701_091805.jpg
This is the front of the jugs where I had the oil leak
20180701_091748.jpg
This is the same picture of the jugs but I have a light put on the top by the bolt hole, you can clearly see the light shining in between.
 

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Your explanation sounds good, the water/dirt theory has been the best existing since Honda doesn't say why there was a change.
David Silver Spares sells new ones with this notation
[h=1]Cylinder barrel (From Engine no. CB400NE 2011713 to end of production)[/h]
This is a modified barrell from the original, this barrel requires cylinder bolts that have rubber seals on the second set in from the left hand side (Front and Rear). Please check if you have these type of bolts, If not, please order one of each of the
following bolts to complete this modification: 90087MC0010 and 90088MC0010.

 

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Discussion Starter · #3 ·
My only thought on the oil lines to the head bolts is to allow some oil around the bolt threads to prevent rust and corrosion below the rubber seal. Had the bike for a run today and all seems to be good so I am confident that the bolts were the solution.
 

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Discussion Starter · #4 ·
Update: I was looking at the 450 jugs tonight, they still require the bolts with the rubber on them, but the jugs do not have the bolts exposed on the 450 like the 400 does. The 450 does still have the oil lines at the base that expose the same 2 bolts to oil, but I assume since the 450 jugs are bored larger (about 1/4 without measuring), that they filled the bolt areas in to strengthen that area. There is no difference in the head, the bolts are still exposed on those.

Hope this helps someone.
 
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