I've always felt that this motorcycle needed some additional cooling because it's never run very well on the hottest days. I'm not 100% sure why Honda decided that the CB900c needed an oil cooler but not the CB750c. Here's my justification for wanting to add an oil cooler to my bike:
- running cb900 cams
- I live in the South
- Bike has always idled differently on the hottest days
- it's another project
There are 2 options to add oil cooling to one of these old bikes. The first
option is to buy a spin on oil filter adapter with ports for oil to flow
into and out of an oil cooler. The advantage of using this approach is the
notion of adding brand new and possibly more technologically advanced parts.
The disadvantage might be cost and full pressure flowing through the hose
which might impact lubrication flowing quickly enough to the engine.
The second option is to swap the parts from a cb900 with the advantage of
having a design/setup that was engineered for this motorcycle by Honda with
a disadvantage of being able to source the parts due to 40 year old parts
becoming hard to find and not beat to death.
Oil Sump (pan): I had a little trouble locating an oil pan but after looking
for a while, found an old dirty one from a seller. The 2 remaining listings
were either not from a CB900 or not a US seller. When I received the oil pan,
it looked as though it had just been removed from the bike. Road grime, oily
and parts of the gasket were still attached. After spraying it down with brake
cleaner and grafitti cleaner I was able to clean off the gaskets and most of
the grime with a nylon brush and a safety blade. The oil pan will not be
clearly visible so I'm not going to polish or paint it so there is no need to
put more effort than I already have in cleaning it in preparation for the
swap.
Oil Pump: this was even more difficult to find since I only found 1 for sale.
This one looked fairly clean and the gasket was mostly gone, but I spent a
little time to clean it up some more just to be sure the gasket surface was
prepped and there were no foreign debris inside the pump. I disassembled
the 3 layers of the pump and found it to be moderately worn with a few gouge
spots where the pump impeller travels and this is supposed to be a bad thing
that reduces oil pressure since the gouged surface will allow pressurized oil
to escape from it's intended destination of the engine or the oil cooler.
The recommendation is to purchase only pumps that are disassembled so you can
examine the wear surfaces. I did find one for sale with the pump broken down,
but it looked to be in worse condition than the one I had.
I wonder if I can fill in those gouges with jbweld and have a lasting
re-surface in this type of application?
I figured it might be a good idea to switch out the 40 year old hoses so I
cut the compression fittings off with a dremel and fitted new stainless hoses secured with a simple hose clamp. Not pretty, but not high pressure and cheap.
I didn't keep the protective spring sleeve for the original hoses, but kept a small section that goes under the rubber bushings where the lines will be gathered and secured to the engine case with the 2 bolts between cylinder 2 & 3. The spring sleeve was cut with a dremel and a cut-off wheel.
With the hoses rebuilt, I waited for warmer weather before I started spending some time in the garage with the motorcycle. This past winter was too cold for me to want to be sitting on the cold hard ground even if it is in a protected and slightly warmer garage.Part swapping went fairly smoothly (I hope). As expected the gasket removal was the most tedious part. I laid the bike on either side to get to the bits underneath a little easier (exhaust had to be removed, so I'll use the opportunity to paint it again). I still had to lay on the ground, but it was easier to see what I was doing with the better angle. I don't have a lift and could have probably used one for this job.
So far, the only stumbling block has been trying to figure out how the oil cooler lines secure to the engine. I had all the parts but couldn't understand how to attach it until I realized that the mount was actually broken and the tabs were missing. Once I figured out what was wrong and where the part should be attached, I was able to fashion a repair to allow me to mount the bracket. I couldn't find this part in the cooler parts diagram because it lives on the cylinder diagram (15528-438-000) but I managed to find a ratty used one on ebay for $22 (I decided to save my money and fix it with stuff I had laying around)
Scrap sheet steel, drill press, angle grinder, and flux welder for the win. The tab needed to be contoured to sit flush due to a slight curvature in the engine case between the bolts.
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| Mount repaired |
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| Tab shaped and contoured |
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| Painted to reduce rust |
I'm anticipating the next hurdle will be mounting the cooler to the frame because it looks like the wiring harness might rub the cooler. I'll also need to relocate the horn, but we'll see what happens when I get there.
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| Lines mounted |
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