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Oil Flow and the Lower Banjo Bolt

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Oil Flow and the Lower Banjo Bolt

PostAuthor: wsudavis » Wed May 17, 2017 11:20 am

I recently read in a thread on VTF that the lower banjo bolt should be fully tapped to 4mm through the shaft of the bolt as far as the transverse channel in the bolt. It was stated that some bolts, due to a manufacturing error, were not fully tapped all the way through. Mine appears to be one that was "manufactured in error." Can anyone confirm that this is a manufacturing error and if it needs to be corrected? My concern is that by drilling out the bolt the rest of the way, I might be decreasing oil pressure to the the top end of the motor and the delivery of oil over the camshafts. If anyone can shed some light on this issue, I would appreciate it. Thanks in advance.

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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: chrismalm » Wed May 17, 2017 5:00 pm

Drilling out the side hole in the banjo bolt will increase oil flow and to some extent, pressure to the top end. The concern is reducing pressure to the bottom end and/or sending too much oil to the top and scavenging the crankcase. I don't remember the recommended banjo bolt side hole diameter. 1/8" is a WAG.

EDIT: 05/19/17
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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: drainplug » Thu May 18, 2017 9:57 pm

I drilled mine out to the same diameter as the rest of the hole (down the center of the bolt) and have done a couple thousand miles without any problem.
Like a car engine the oil runs down the cam chain galley back to the sump so that shouldn't be a major concern.
IMO, can't imagine there would be a problem with pressure to the bottom end since it is primarily splash lubed,
though some may be pumped to the trans.
I am about to do a trip with a friend to Death Valley so maybe I'm wrong, but I will find out soon enough.

I have a 1982 920 parts bike, the guy told me it trashed the front cylinder on the first owner, he rebuilt it and did it again
to him.
Bike only had 5,300 miles.
Sure enough I pulled the bolt and had a hole about as big as a pencil lead!
Got it for $100
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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: DGA » Fri May 19, 2017 12:06 am

The oil pump is two stage, one feeds the crank and bottom end, the other the cam feed. By drilling the banjo bolt, you feed more oil to the cams, and it will not hurt the bottom end pressure. Drill up the center of the bolt, I don't remember what size I used, not sure too big is bad though. I did notice after I did mine that the oil level light came on more, so it will pull more oil out of the pan and keep it up top, so make sure the level does not get low. Replacing the cam bearings with ball bearings is a low cost, good thing to do as well, and not hard to do.
'81 XV750, clip ons, 18" rear wheel, lowered 920 forks with twin discs and 1.5" spring spacers, 1100 brake master cylinder with CNC billet cap, -3 braided brake lines, lowered instruments and headlight, CNC billet mirror mounts, small billet turn signals with running lights, Koso tach/ speedo, stainless 2 into 1 stepped headers with reverse cone muffler, starter heat shield, 4 guage starter cables, rear exhaust heat shield, 4" round open air filter with billet CNC mount, TM38 flat slide Mikuni carbs, XV700 ported heads, BT-C05 cams, colder BP8ES NGK plugs, stiffened swingarm, polished engine side covers, polished rear peg mounts with carbon cover panels, single horn relocated, Sparto tail light with 3D printed lens, BSA tank kneepads, one off carbon fiber cafe seat with brown cover, fork gaiters, KDX200 rear shock, single tach/speedo with carbon fiber dash, red LED under tank and seat lights, black pearl paint with silver accents.
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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: chrismalm » Fri May 19, 2017 12:38 pm

:yup: DGA's right, its a 2 stage pump. Bottom end pressure not directly affected by drilling bolt.

Score on your 920, Drainplug ! Have you torn into it to see what it needs ? I paid a lot more for a similar 920. A good used piston, cylinder, cam, rockers, chain, guides, new rings and lapped valves for the bad cylinder and I was back on the road.
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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: drainplug » Fri May 19, 2017 4:16 pm

That was about 4 years ago.
The front head and cylinder were trash.
Sold the frame w/pink to a member here and sold a few other parts.
Has a new #2 gear, got a 4 brush starter, clutch should be near new if I need one, carbs etc.
Just had to hide from the ole ball and chain for a while.

I tell ya, these things are like cats, if you have one you have a flock!
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Re: Oil Flow and the Lower Banjo Bolt

PostAuthor: mark75 » Fri May 19, 2017 4:55 pm

drainplug wrote:I tell ya, these things are like cats, if you have one you have a flock!


it's called the "Virago Virus", very contagious. :lol:
The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
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