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Author Topic: CB400F Crankcase Oil Leak  (Read 584 times)

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Offline calj737

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Re: CB400F Crankcase Oil Leak
« Reply #25 on: October 03, 2018, 03:26:19 am »
He's talking about these bearings:
https://images.cmsnl.com/img/partslists/honda-cb400f-1976-usa-crankshaft_bighu0235e7014_e74d.gif

The crank is fitted to the cases with specific bearings to that pair (crank/case)
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Offline Little_Phil

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Re: CB400F Crankcase Oil Leak
« Reply #26 on: October 03, 2018, 07:08:50 am »
On the 500 each of the 5 main bearing case locations are graded A B C according to slight variations in size in the manufacture of the cases. The cases are stamped at the rear to show the grading. The shell bearings (part 6) are then selected depending on this grading AND measurements of the crank journals. So at manufacture the whole cases, crankshaft and bearings are a set. There were about 5 or 6 different sizes of that part no 6.
Not sure if this applies exactly to the 400, but is will be similar.
If you buy the cases make sure that the bearings are included and importantly left in their original location. (they are nigh impossible to check and any marking will have long since disappeared.)
If the bearing surfaces look good, you can then Plastigauge the bearings to check if they may be good for your crank.

Offline jakec

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Re: CB400F Crankcase Oil Leak
« Reply #27 on: October 03, 2018, 08:55:50 am »
Thanks guys this is really helpful information. I will contact the guy with the cases and tell him what I need. Is there anything else that I need to worry about that can be specific to the cases? I'm sure he will be willing to include other parts if I need them.

Are those large objects on the crank counterweights for the pistons/jugs?
1975 CB400F
1972 CL175 K2

Offline calj737

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Re: CB400F Crankcase Oil Leak
« Reply #28 on: October 03, 2018, 11:10:06 am »
Are those large objects on the crank counterweights for the pistons/jugs?
Those are the crank lobes. Yes, counterweights in a manner of speaking. The piston clamps between the lobes.

With respect to the cases/bearing shells, you would use your crank, pistons, and piston bearings. But you need to confirm using Plastigauge what main bearing shells (crank bearings) you require. The Plastigauge is bought at the auto store, you drop a dab under the crank, torque the crank into the case, release the crank and measure the width of the dab. That tells you the bearing thickness you need.

You can locate the bearing IDs on your case at the rear of the case, stamped into it. If by chance the letters are the same on yours as the new set, you're in business. If not, you need to do the plastigauge to purchase and install the correct shells.
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Offline jakec

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Re: CB400F Crankcase Oil Leak
« Reply #29 on: October 08, 2018, 09:19:38 am »
I received photos of the cases from the engine he stripped down. He says there is similar damage near the boss, but not penetration into the oilway (he says this engine never leaked). Do you think that this would be repairable considering there was no penetration into the oilway? If not, he says he has a complete engine he'd be willing to sell me.



1975 CB400F
1972 CL175 K2

Offline jakec

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Re: CB400F Crankcase Oil Leak
« Reply #30 on: October 19, 2018, 09:12:07 am »
Ok so here are my options. I would appreciate some advice although I think I know which way I am leaning at the moment.

Option A is to purchase the cases I showed above, with damage. Asking price $100. Seller says the engine they came off of was dry so he doesn't think the damage ever caused a leak. I could see about having these cases welded and then rebuild my motor into them.

Option B is to purchase this motor. Asking price $325. Seller wants to keep the electric start and kick start (I guess he needs these parts). He said he would include them if I needed them (but I don't really). He also said that it "sounds like low compression" in one cylinder so he suggests a top end job before throwing it in my bike. I'm ok with doing a top end.





1975 CB400F
1972 CL175 K2

Offline calj737

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Re: CB400F Crankcase Oil Leak
« Reply #31 on: October 19, 2018, 01:46:20 pm »
What does "low compression" sound like?  ??? ::)

A leak down test would be the better diagnosis of engine health. Low compression, even loss of pressure during a leak down could readily be valves out adjustment. Or, engine wear. Won't know until you poke around some.
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Offline jakec

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Re: CB400F Crankcase Oil Leak
« Reply #32 on: October 19, 2018, 02:12:39 pm »
I'm not sure, he said he has been a mechanic his whole life and that was just his impression when the cranked it over (never seen it on a bike, he bought it benched). If I buy an engine for $325 and then ship it.. I think i'm up there in the $$$. I asked someone I know who has shipped an engine and they said it was $250.

I guess option C is a top end / head gasket on my current engine and continue to deal with the crankcase oil leak. I hate that it leaks (always having to top off). Maybe I can reduce the leaking by 25-50% if I fix the top end leaks, though. That option starts to look more attractive when I think about $500 just to get another engine with unknown issues.
1975 CB400F
1972 CL175 K2

 

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