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  • In order to help others find info on a particular bike, be sure to put the year, make or model of bike that you are asking a question about, in the Topic Title. This will allow people to pass by posts they have no interest in.

1974 Honda CB450 K DOHC

Vmass

Vmass

Forum Sage
Past Site Supporter
I have had this bike for a couple years now. Pushed it aside a couple of times for other projects. When I bought the bike it had been sitting idle for nearly 20 years. I did the carbs, valves etc and got it up and running and thought all was good. It is actually almost completely done with new tires, brakes, petcock etc.

The other day I found that the compression is one cylinder is 90 psi, while the other is 150 psi. Poured a little oil in the cylinder and the psi jumped to 130 psi, indicting rings.

So, this is a turning point with the bike. I need to decide whether I want:


1) Tuck it away or another 20 years.

2) Sell it to someone who will do the work, I would price it high enough so it doesn't end up as a parts bike.

3) Attempt the repairs myself, I am not much of a case cracker, mainly due to my skill set and time constraints.

4) Research and find a specialty shop that will do the work, I have heard good things about this one: http://www.madhousemotors.com/

Just thinking out loud here....I would love to learn more about this engine, but I think doing this one myself is my least favorite option.

Does anyone here have experience with this bike?

 
Change the oil, adjust the valves, plate it and ride the snot out of it.
 
That's a fine looking bike. Like rustybronco said ride the snot out of it . The compression will most likely come back up ,probably a stuck ring from sitting.
 
yank said:
That's a fine looking bike. Like rustybronco said ride the snot out of it . The compression will most likely come back up ,probably a stuck ring from sitting.
Click to expand...


Well, that would be nice!!
 
I agree. Ride the snot out of it and abuse the throttle.... way up and way down.... and yank that piston around a while..then recheck the stats after a few weeks of rattling its cage

Oh and by the way, that was the first street bike i ever rode on pavement.
 
Last edited:
Sounds likely, it usually works on GSes that have been sitting. Run it hard for a month and check it again. Even if it does need rings, the top end on a twin is easy to do. Several hours worth of work is all, even if you have to spend a bit of time reading about it. Find a high school auto shop class to do it if you can't spare a few hours to do it yourself. Maybe there's a motorcycle mechanic shop in the local community college or trade school that does stuff like this?

Or just pay someone who works on old motorcycles, like someone on this forum maybe. I'd do it as that model has always interested me, except I have way too many projects going...

I would think that model in that shape is worth paying to have it fixed? Whatever you do don't take it to a place that sells new bikes, their job is NOT to keep old bikes running forever.


On second thought, 90psi in one cylinder is NOT going to cause it to run like crap. I have run many many bikes with lower compression than that, they mostly run OK. Lopsided idle maybe, could be a bit hard to start, perhaps a tad down on power but that's about all. Going down the road you'd never know it. It could cause it to foul a plug but that's not too likely. If it is truly running bad I'd look at the carbs, they always go bad from sitting. Also look at the ignition points. And all of the usual places where neglect shows up.
 
tkent02 said:
On second thought, 90psi in one cylinder is NOT going to cause it to run like crap. I have run many many bikes with lower compression than that, they mostly run OK. Lopsided idle maybe, could be a bit hard to start, perhaps a tad down on power but that's about all. Going down the road you'd never know it. It could cause it to foul a plug but that's not too likely. If it is truly running bad I'd look at the carbs, they always go bad from sitting. Also look at the ignition points. And all of the usual places where neglect shows up.
Click to expand...

Actually forget the hard to start and down on power part. Those are the ones with about ten psi in one cylinder.
 
Maybe a little down that jug as well and let it set a day or two..then run the smoke off by going for a long spirited ride.
 
Well, this is strange. Yesterday after reading the suggestions of adding a little sea foam in the case, I did just that. I also put a straw full down the jug. Immediately after doing this, I checked the compression with a different gauge ( and without my Honda Helper). I came up with 190 psi in both sides.

I decided to fire it up and it ran poorly. The side that I thought had low compression was not running as hot as the other side. Some misfires and just doesn't sound right.

Fast forward to today.... I decided to check the compression again, thinking that maybe adding the sea foam to the jug gave me a false reading as it coated the bad rings? Well, after 24 hours + of sitting I get a reading of 190 PSI in both cylinders. Each time the compression was checked while the engine was cold and the carbs on. I know this is not correct, but consistent.

So, I guess the good news is I have a crappy running bike with good compression. Back to the drawing board!
 
It was carbed, timed, condensed and valved.................I will do it all again.
 
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