CB360 engine rebuild

Just picked up a ‘76 CB360T. It was 22,000 miles but is all in stock condition and I do not believe the engine has ever been rebuilt. It runs but something doesn’t quite sound right and I believe there is a slight knock in the left cylinder. Haven’t measured compression yet.

Even so, I’m anticipating a rebuild and would like advice on what I can do to inject a bit more performance into this motor. I’ve seen the gs850 swaps and trying to figure out if this would be worth time and money. I have about $2k to spend on the entire rebuild. What else could I do to improve performance and/or reliability?


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Lnb001 said:

Just picked up a ‘76 CB360T. It was 22,000 miles but is all in stock condition and I do not believe the engine has ever been rebuilt. It runs but something doesn’t quite sound right and I believe there is a slight knock in the left cylinder. Haven’t measured compression yet.

Even so, I’m anticipating a rebuild and would like advice on what I can do to inject a bit more performance into this motor. I’ve seen the gs850 swaps and trying to figure out if this would be worth time and money. I have about $2k to spend on the entire rebuild. What else could I do to improve performance and/or reliability?

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Could just be the valves need adjusted. I'd try a few things before just tearing it apart right away.

I'd adjust the valves, cam chain, etc as recommended earlier. One thing about 360s though is that they got their oil filters cleaned very rarely because it was so much work to do so. Sometimes this starved the top end for oil and the cam journals got wiped out. Makes a lot of noise when it's running.

The centrifugal oil filter on CB/CD 175 through CB450 does not get blocked, even at high mileages (>70,000).The cam bearing oil starvation has a completely different reason, the oil transfer piece cannot maintain pressure at high rpm. The other reason is blocked oil pick up, particularly if anyone has used silicon sealer on motor or covers. I think that most people don't understand how the oil filter works. It's actually way more effective than any paper filter can ever be and will remove sub 10 micron particles. Paper filters ALWAYS open bypass when pressure is too high, often on start-up and high rpm even with recommended grade oils and hot engine (Yes, it means you often get unfiltered oil going around motor) Cam chain adjuster is probably stuck if it wasn't adjusted regularly, most probably pivot is damaged so will need some 'brute force' to adjust. The alternative is full engine strip. Of course, It's a real smart move to check everything 'adjustable' first.
BTW, isn't 76 a CJ not CB?

I wasn't aware of an oil transfer piece (learned something new today), but I didn't say that the filter got blocked either. The centrifugal filter reaches capacity at a certain point and then there's no filtration which leaves all that metal and clutch material to find a new home, which sometimes ends up restricting an oil passage (which was my assumption about the top-end starvation). I think it's good advice on these engines to clean out the filter and pickup screen prior to startup when you acquire them.

Yep, it's a good idea to clean oil pick up and filter,. Usually pick up has far more debris than any other part of system. The oil transfer piece is in clutch cover. Oil comes from pump through drilling in crankcase to clutch cover, into filter then out again through a different drilling in clutch cover to oil passage along back of crankcase below cylinders, some diverted to cam bearings and whats still under pressure goes through transmission bearings and shafts eventually coming out through clutch. The 'filter' is a 'cup' about 1.75" dia and 2+" long on the end of crankshaft , spinning between 1000 and 10,000 rpm. The more you rev, the more efficient it is. In 40+ years of working on 'OLD' Honda's ('most were nearly new when I started) I've never seen one 'full The worst I've seen had a layer about 1/4" thick,. At around 20,000 miles it will be less than 1/8" thick even if it's had minimal oil changes The only time it gets real nasty in there is after something else has already failed (clutch plates, big end rollers or low pressure because transfer piece 'opened' and acted as a pressure release dumping oil back into sump. Even then, the big ends, main bearings and transmission will still be fine as enough oil makes it to the oil gallery to keep things working until cam bearings fail (not enough pressure to get through oil jets up to head) There are a couple of threads on here about modifying oil transfer piece, I would recommend it on any Honda that uses centrifugal filter. (even the 50's and 90's)

crazypj said:

Paper filters ALWAYS open bypass when pressure is too high, often on start-up and high rpm even with recommended grade oils and hot engine (Yes, it means you often get unfiltered oil going around motor)

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If 360s had a bypass valve in a filter or pickup, they maybe wouldn't have the issues. The whole point of the bypass valve is to let oil circulate when the filter is either clogged or the oil is too thick to pass through the filter (like when it's cold). It's better to sling unfiltered oil for a few minutes than no oil at all.

Any updates Lnb001?

Yea I found the bottom ring on left piston snapped in half when I took the block off. Not sure if that was the cause or not. Compression was excellent in both cylinders before disassembly. The block is now at my machinist getting bored out to 69mm for the gs850 pistons. He estimates 3 or 4 weeks and $100 per jug. Also getting it bead blasted.

In the meantime, removed valves and will check clearances. And also trying to sort out what I want to do with the seat. I hate the stock seat. The foam is in good condition so I’m considering trimming it down and recovering with some custom upholstery. My mother in law is an excellent seamstress by hobby so I have her to help me with this.


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irk miller said:

If 360s had a bypass valve in a filter or pickup, they maybe wouldn't have the issues. The whole point of the bypass valve is to let oil circulate when the filter is either clogged or the oil is too thick to pass through the filter (like when it's cold). It's better to sling unfiltered oil for a few minutes than no oil at all.

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The problem is, the oil transfer piece acts as a bypass valve. The oil is always filtered with centrifugal filter but when bypass opens, the pressure delivery to main gallery drops so no oil gets to head and cam bearings seize. There are a couple of ways to fix the problem, easiest being modify transfer piece.
This happens on all Honda's with same or similar system, from CB160's, CB/CD175, CB350's right through to CB450/500T. with plunger oil pump BUT, only if operated at sustained high rpm. The 360, having a trochoidal pump, makes things worse not better as pump is more efficient.
Lnb001, glad you found simple (ish) problem. Seat is OK if your actually going anywhere over 20 miles but it is pretty bulky looking. I would get higher density foam if your looking for something smaller, the stock foam cut down is too soft to be useful.

crazypj said:

The problem is, the oil transfer piece acts as a bypass valve. The oil is always filtered with centrifugal filter but when bypass opens, the pressure delivery to main gallery drops so no oil gets to head and cam bearings seize. There are a couple of ways to fix the problem, easiest being modify transfer piece.
This happens on all Honda's with same or similar system, from CB160's, CB/CD175, CB350's right through to CB450/500T. with plunger oil pump BUT, only if operated at sustained high rpm. The 360, having a trochoidal pump, makes things worse not better as pump is more efficient.
Lnb001, glad you found simple (ish) problem. Seat is OK if your actually going anywhere over 20 miles but it is pretty bulky looking. I would get higher density foam if your looking for something smaller, the stock foam cut down is too soft to be useful.

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Ok good call on high density foam. Original reason for cutting down foam is so I could use stock seat pan and not have to fabricate something custom, but I’ll take this as an opportunity to learn.


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