Topic: At what point does a SOHC become "high mileage?"

[Holden]

I have a '74 CB750 with 31k miles.  It has mid 150's to mid 160's compression across all cylinders.  It revs freely and shifts well.  Would you consider it high mileage? 

How many miles do you have on your bike?  What do you think one can expect from a properly maintained CB750?

[MCRider]

Properly maintained, should go 100k+. The real issue now is shear age. All the rubber bits get hard, cables get corroded internally, etc. Swingarm bushings likely are seized if they've never been serviced. (Rrequires disassembly).

[BoCoJohn]

I have a 1973 CB 750.  It has 21,000.  I would consider 10K low, 20K about average and anything above 30K starting to get high.  Even though I am sure these bikes can go well over 50K running nicely if properly maintained.

[HondaMan]

MCRider has it right, if the oil was changed on schedule and 20w50 oils were used. If 10w40 oils were used, the rings and valve guides will be done at about 50k miles, tops, and the rod and crank bearings will be worn to near maximum clearance, needing replacement. So will the primary chains and cam chain. The 20w50 oils will keep the chains together far longer: mine have nearly 140k miles on them, now, and are reaching their wear limits.

Don't confuse the 750 with the wet-sump bikes, like the Kawis, Suzys, and Yamahas, or even the Honda 500/4 and 550/4. In terms of engine life, the 750 is essentially a car engine by comparison, due primarily to the high-volume oil system and dry sump oiling. In other words, it is SERIOUSLY overbuilt for the HP it develops in stock trim. 

[bollingball]

My 750 K8 has 25000 I would say it is just broken in good. Like MC said it is the rubber bits if no leaks no problem. Mine smoke a lot when I got it after sitting 6 years but I knew what to do and after oiling the cyls. a few days and 100 miles it stopped and has been fine for 2000 miles. The worst thing for these bikes is improper storage

                             Ken

[BoCoJohn]

Hondaman,

Would you suggest running 20W-50 in all the K 750's even with low mileage ?  I've always been one to follow the factory specs.

[MoMo]

I have three 750s,  40000 miles properly maintained-no problems whatsoever, 19000 miles poorly maintained-broken engine case,  17000 miles poorly maintained-seized.  MC Rider and HM are right-100000 is easily obtained with proper oil and maintenance...Larry

[fmctm1sw]

Hondaman,

Would you suggest running 20W-50 in all the K 750's even with low mileage ?  I've always been one to follow the factory specs.

Yes, please tell.  I LOVE oil threads!

[Greggo]

Don't confuse the 750 with the wet-sump bikes, like the Kawis, Suzys, and Yamahas, or even the Honda 500/4 and 550/4. In terms of engine life, the 750 is essentially a car engine by comparison, due primarily to the high-volume oil system and dry sump oiling. In other words, it is SERIOUSLY overbuilt for the HP it develops in stock trim. 

Is this to say with all things equal, my 500/4 engine will need a rebuild before a 750?

[bollingball]

No it just needs 250 more cc's 
Now the big bore guys can pick on me

[TrueSpin]

Yes, please tell.  I LOVE oil threads!

I think if it were HondaMan's answer, it would be "oil post" not "oil thread". I don't think anyone would argue.

[Stev-o]

I just bought a K4 project bike with 48K miles and do considered it high. It starts right up and runs good, I believe it was properly maintained by it's 2 previous owners.

[anotherCB]

Bought a K7 with 38,000 mls on it. It was running when I got it. I have already put 1,000 mls on it without doing anything else but cleaning the carbs, adjusting the valves and points. It runs great, doesn't smoke, pulls strong and I consider it a "teenager". Lot's of life left (but I plan to keep an eye on cholestorol and blood pressure  )

[HondaMan]

Hondaman,

Would you suggest running 20W-50 in all the K 750's even with low mileage ?  I've always been one to follow the factory specs.

I'm not sure what you're referencing: Honda has always called for 20w50 oil in the 750 at summer weather temperatures. Their Owner's manuals were sometimes misprinted and showed 10w40 (on the post-1976 bikes), and on the smaller Fours the dipsticks were labelled 10w40 as the MINIMUM weight allowed (although this was largely 'lost' to the general public in the years since).

[HondaMan]

Don't confuse the 750 with the wet-sump bikes, like the Kawis, Suzys, and Yamahas, or even the Honda 500/4 and 550/4. In terms of engine life, the 750 is essentially a car engine by comparison, due primarily to the high-volume oil system and dry sump oiling. In other words, it is SERIOUSLY overbuilt for the HP it develops in stock trim. 

Is this to say with all things equal, my 500/4 engine will need a rebuild before a 750?

In a word, yes. At about 40k-50k miles, typically. Those rings usually lose their seal on the outboard sides of the #1-#4 cylinders, causing oil burn and lower compression, especially if the bike is now ridden infrequently. The only exception to this that I have seen is on 500/550 bikes with full touring fairings with lowers: they get a little more mileage because the temperatures across the cylinders is a little more uniform, and higher. this lets the bores wear more evenly on the outer pair.

[octagon]

i know cars are different, but there are rough similarities between the old vw engines and cb750 motors.  i ran the living #$%*e out of a couple of vw bugs and one bus in earlier days, before and after rebuilding their engines, and i found they all ran noticeably better on 20w50. the next best was straight 30w shell rotella. i even tried straight 10w shell oil on one bug - a guy i knew ran his old john deere tractors on that for some reason, and he talked me into it. trashed the motor in about two thousand miles.   

[Greggo]

This will not turn out well.

[sick_seven_fifty]

You guys use what you want.  I won't use anything but 3-IN-ONE oil...sometimes I make an exception and use a 3-IN-ONE, Extra Virgin Olive Oil blend (smells tasty).  Purrs like a kitten.  The only problem is that it takes so many of those damn little drip bottles to fill it up.

[MoMo]

You guys use what you want.  I won't use anything but 3-IN-ONE oil...sometimes I make an exception and use a 3-IN-ONE, Extra Virgin Olive Oil blend (smells tasty).  Purrs like a kitten.  The only problem is that it takes so many of those damn little drip bottles to fill it up.

You should try the vestal virgin olive oil ...Larry

[HondanutRider]

Love "oil threads"!
Just to report on what has happened along the years with Honda motorcycles (post SOHC-4 era), as I have experienced it, my 2003 Goldwing just turned-over the 100,000 km mark today.   It happened along a nice and empty stretch of highway, so to celebrate the occasion, with the odo still reading the 100k, I blasted it up to top the ton.  My Garmin was operating and recorded my max at 163 kph.  The Goldwing still runs and performs flawlessly as when new.
In the entire 100k life I've ridden this Honda, I've had nothing to do but the regular maintenance that I perform myself every 10,000 km.  This includes a new filter with 10W40 Honda motorcycle oil.

[Simpson]

MCRider has it right, if the oil was changed on schedule and 20w50 oils were used. If 10w40 oils were used, the rings and valve guides will be done at about 50k miles, tops, and the rod and crank bearings will be worn to near maximum clearance, needing replacement. So will the primary chains and cam chain. The 20w50 oils will keep the chains together far longer: mine have nearly 140k miles on them, now, and are reaching their wear limits.

Don't confuse the 750 with the wet-sump bikes, like the Kawis, Suzys, and Yamahas, or even the Honda 500/4 and 550/4. In terms of engine life, the 750 is essentially a car engine by comparison, due primarily to the high-volume oil system and dry sump oiling. In other words, it is SERIOUSLY overbuilt for the HP it develops in stock trim. 

Interesting observations... Thanks for posting!