[androu]

Greetings. Recently picked up a 71 CB450. Garage queen with 15,000 on it if the odometer is right. Tested compression, and super low, about 65 on both cylinders. Adjusted the valves (tricky and weird). Three were a little tight, exhaust on the left side had the mark on the adjusting screw 180 degrees out. Compression is a bit better, now about 90 on both sides. Seems likes a top end rebuild might be in order. Can anyone recommend a good shop in the SoCal area?

 

[jd50i]

Rings might just be stuck from sitting. Some members have used a mixture of acetone and automatic transmission fluid in the cylinders to free them up. Did you have the throttle wide open when you checked compression?

 

[androu]

I had the engine open, choke open, throttle wide open. Best I got was about 80 on both sides.

 

[J-T]

Compression test on a cold engine that's been sitting for years is pretty much irrelevant beyond telling you that there is some there. Soak the cylinders with whatever penetrating fluid you prefer (acetone/ATF for me), get it running, ride it a couple hundred miles, then check the compression and go from there.

 

[Rob Axel]

... everyone touts a compression test.. YES, it is good .. but it is only one test.. and tells you one thing..psi of what that cylinder produces..
Add into this a "leak down test" along with the compression .. it will help direct where your problem my located...
It will let you know if it's your rings, intake or exhaust valve, head gasket or leakage other than "rings"...

 

[spirograph]

What? The guy is looking for someone to do a top end rebuild for him, and you think he has a leakdown test kit on hand? I’m with J-T - if it runs, ride it.

If it doesn’t, we can walk you through a top end rebuild. If you don’t want to do that, someone might have a shop recommendation. Forum member TOOLS1 does great machine work that’ll get you halfway there.

 

[76TWIN]

Also depending on the gauge used, your compression readings may be wildly inaccurate.

 

[Rob Axel]

Well, not exactly sure where he is located.. but a lot of "auto part supply" stores will loan you tools to include a leakdown tester..
Plus, they REALY aren't as expensive as you think.. it will let him know atleast if his problem is rings or valves.

 

[spirograph]

A teaspoon of motor oil will let him know if his problems are rings or valves.

 

[tbpmusic]

Well, not exactly sure where he is located.. but a lot of "auto part supply" stores will loan you tools to include a leakdown tester..
Plus, they REALY aren't as expensive as you think.. it will let him know atleast if his problem is rings or valves. View attachment 246737

Gotta have an air compressor for a leak-down test.......

 

[Rob Axel]

Not true... you need a supply of air... this can range from a 02 bottle from a welding torches, or even a storage tank you fill at your local gas statiOn to add air to tires at home..
Yes, it is easier with a nice size compressor ..
if it runs.. ride it over to a shop (anything that has s compressor) bring a wrench to remove the plugs, install the tester.. when your done, replace the plugs and ride home..

 

[JamesPal]

Have you tried to start it?

 

[SuperFudd]

I had the engine open, choke open, throttle wide open. Best I got was about 80 on both sides.

I wonder if bad rings is a common failure at around 15000 miles on these 450s. That happened to one cylinder on my CL450 K5. Compression shot up temporarily with a squirt of oil into the cylinder so not valves. Compression slowly lowered over ~5000 miles.

 

[jseconds77]

To the op. Welcome!
be careful cuz this is not a question of just finding a shop, you must find one experienced with vintage and classics. Depending on where you;re located estimates can vary wildly but I bet, I just bet quotes of 1,000 dollars and up won’t be unheard of. If you still decide to pay up and enjoy owning it I guarantee that other things, at times costly things will come up. This is the big judgment call for you. Me? I scored mine cheap and it ran, idled, and was titled but man did I spend $$ once it had some needs cuz at the time I was just getting my feet wet with it but as time went on, thanks to this crew I improved but I still spent a lot of time researching and tracking down various parts....not even factoring the amount of garage time I put in. Yikes.

now? I made a deal with myself: do all I know how to do, spend $ reasonably for things I don;t and knock on wood, if something big and costly happens I gotta hang it up as I put too much $$ in over the years. Just think it over before you proceed cuz even the most carefully restored bike STILL needs some kind of attention and parts? Well, even if new etc. everything works....until it doesn’t. $$

good luck and you came to the perfect place. ��