Looking to buy a CBX-- What issues to look for?

CBXs, new bikes, old bikes, cars, trucks, general chat, off topic, this is the place to post it.
Post Reply
KC_CBX
New Member & Happy To Be Here
New Member & Happy To Be Here
Posts: 3
Joined: Wed Nov 11, 2015 8:13 pm
Location: Ely, Minnesota
Location: Ely, Minnesota

Looking to buy a CBX-- What issues to look for?

Post by KC_CBX »

I have decided my CB750 K1 needs a buddy and so have started looking for a 1979 CBX.
Its not my first rodeo for vintage bikes , so I know all the basics to check over on a prospective bike, but are there any
known issues related to a 79 CBX that I should check?

Thanks,
KC

daves79x
ICOA Technical Director
ICOA Technical Director
Posts: 4738
Joined: Sun Oct 01, 2006 8:05 am
Location: Knox, PA
Location: Knox, PA

Re: Looking to buy a CBX-- What issues to look for?

Post by daves79x »

I can gladly run down a checklist, as well as can many others here, but there are several threads on this exact subject that you can search first. Give it a quick try and if you can't find anything, we'll give you the scoop. Welcome!

Dave

EMS
ICOA Member
ICOA Member
Posts: 10151
Joined: Wed Mar 05, 2003 7:55 am
Location: North East OH, ICOA 3904

Re: Looking to buy a CBX-- What issues to look for?

Post by EMS »

The only two things that stand out from other used bikes with most common issues are the carburetors and the alternator. Check how the bike runs and if the charging system is O.K.
And then, all the other things you usually look for.

rpleines
ICOA Member
ICOA Member
Posts: 107
Joined: Sun May 22, 2011 12:32 pm
Location: New Haven, CT
Location: New Haven, CT

Re: Looking to buy a CBX-- What issues to look for?

Post by rpleines »

Copied from an article that appeared in Classic & Motorcycle Mechanicals and posted on/at

http://www.cbxclub.com/davespage/cm&m_v50-1.html

GENERAL NOTES
USUAL problems with the Honda six cylinder engine are:
• Burnt exhaust valves. If you use a bad six-into-one exhaust system the exhaust valves will burn out. They can also burn out with a standard system if the header pipes are not securely fixed into the head and properly sealed. The motor then draws in air and runs weak. This can happen on any cylinder.
• Oil consumption. All the original unfaired CBX models suffer from high oil consumption at sustained high speed, especially at over 100 mph. The cure is included in the stripdown story.
• Cylinder head gasket leak. Easily cured by the new, type Honda gasket (Part No 12251422010). The new one has adhesive around the oil gallery holes and around the cam chain tunnel. A blown gasket can be a reason for high consumption because the crankcase can be pressurised and blow oil out through the breather.
• Head studs. Early engines could snap the tops off the cylinder head studs when the engine was switched off after a long hard run. This was caused by the extra heat from the engine, deprived of cooling air, expanding the stud and snapping it at the top. Honda introduced stronger types of studs for the three different lengths of studs. 220mm - part no 90031422003. 217mm - part no 9003442203. 222mm - part no 90039422003.
• Chain wear. The camchains wear, also the primary, chain. This is normal wear, but Honda introduced an improved chain, ie the top chain that joins the two camshafts for longer service life. Average life for these chains (all three) is about 50,000 miles.
• Alternator brushes. They wear out extremely rapidly. You can tell when the brushes are going because the voltmeter starts to behave in an erratic manner. But even this isn't a guarantee that the brushes are worn out. The only way to properly check is to remove the alternator which is an easy job (done in the frame) and check them with the best method known to man - eyesight! So, if you have a flat battery all the time or erratic charging, suspect the brushes.
• Poor starting. Especially common if the bike has been left standing for a long time. It’s inherent with all the CBX models. John has never found a satisfactory reason for it but puts it down to the vacuum fuel tap. It seems to take a lot of cranking to fill all the fuel bowls. To alleviate this slightly, apply full choke; knock the kill switch to 'off’; spin the engine until the oil pressure light goes out; pump the accelerator pump by twisting the throttle fully open half a dozen times; then leave the throttle off, turn the kill switch to 'on', keep choke fully on, and within 15 seconds it should start to fire. This may. not be immediately on all cylinders but they soon fire up once two or three are going.
• Clutch chatter. An inherent problem that can be cured completely. but it's expensive. It can be done by using a different clutch outer off the CBX-B or C models (which don't suffer). But first balance the carbs. This can cure up to 75 per cent of the rattle usually. If it doesn't cure it completely, then the B or C clutch outer, which features cush drive springs rather than rubber is the answer, plus new rubbers on the primary chain hydraulic tensioner oil feed. On the non-B and C engines the rubbers tend to harden because of the heat of the oil, and play develops in the clutch outer which then causes it to start chattering - a horrible noise. Also, the tensioner can crack or become hard and as a result oil pressure is lost to the tensioner. Thus the primary chain is not properly tensioned and this aggravates clutch chatter. With worn rubbers pressure can go down from the direct 64-74 psi at 4000 rpm to about 30 psi.
• Gearbox. Fourth gear is a problem, mostly fixed under warranty by now. If your bike shifts well, leave it alone. If it shifts badly, the box will have to be inspected. The problem is with fourth gear which will need replacing. On early engines the track on this gear was not machined correctly and wears rapidly. Some bad shifting can be put down to the gear pedal pivot which wears rapidly on all machines. This takes only an hour to fix and is very cheap. Replace the change pivot bolt (Part No 90101422000) and this should improve the gear change.
• Oil change. John recommends changing the oil filter every 2000 miles and the oil every 1000 miles to keep these engines in top condition. Some engines he has stripped (even as high mileage as 90,000 miles) have been factory, fresh because the oil has been changed regularly. Other 20,000 mile engine without the same treatment have insides that are black. The CBX can suffer problems, especially if not cared for, but generally there are very few real problems with this magnificent and smooth six cylinder engine.

Following quote copied from a good article posted on the following site:

http://www.carolenash.com/insidebikes/n ... 45-cbx1000

If you’re simply collecting, then the condition of the cycle parts, not the engine, should be your main priority. Engines can be re-built and nobody can see if the piston rings are pattern parts, or original.
Hope this helps. Rich
Rich Pleines

Post Reply

Return to “Daily Discussion: By, For & About CBXers”