Topic: Rebuild Question...

[AEngelsrud]

OK, so I'm progressing along nicely with my '74 CB550K.  I've gotten a good portion of it torn apart and I'm in the process of cleaning and polishing various parts - carbs, front forks, handlebars, controls, tank, petcock, etc.  What I haven't touched yet is the engine.  What I'd like to know from all of you is what are the benefits/drawbacks of pulling the engine off the frame and rebuilding that as well.  There were no major leaks and prior to starting my build the bike was running (badly and not for long).  Also, what are the additional costs that I can expect if I crack the case aside from a complete engine gasket set?  I have no desire to modify the engine in any way so I will not be doing anything to the cylinders or anything else.

I will add that I got this bike as a learning exercise as I have very limited experience with engines and it seemed like a solid place to start.  Is this more than I should take on?

Thanks for any advice you all can provide.

Aaron

[tlbranth]

'twere me, I'd give it a compression and leakdown test and leave it be if it passes. The bad running is probably due to external factors i.e. carburation & ignition.

[bryanj]

If you pull the engine you will need a Gasket Kit, Complete seal kit, And if going that far Primary and Cam chains

[luap]

find out the problem first I might do a compresion test an a leak down test on the motor to see if that is why it ran poorly to begin with. If it shifted through all 5 gears an didnt leak IMO i wouldnt crack the case
But if you do vesrah gaskit 100.00 seal kit 40.00 rings 100.00 hone 100 lapp valves 100 bearings 30-40 bucks
impact driver 10.00 vcb clutch plates an springs 45ish stainless bolt kit 40.00
get a good shop book, label an platic bag your parts use the right tools an ask questions an enjoy yourself.
Is this more than I should take on? thats up to you
paul

[Brantley]

+1 on all above advice. It may be more prudent to make it a learning to tune exercise first (and will be less expensive). Turning wrenches is fun, taking stuff apart is fun. Putting stuff back together can be confusing and frustrating, but I reckon this forum might not exist otherwise. If you go for it I'd recommend:

A digital camera that you don't mind getting greasy and taking several photos of every assembly you break down that isn't a complete no-brainer to reassemble. "Ah, I'll remember how that goes together" generally turns into "Aw, crap, how does this go together?" in my experience.

A Honda parts catalog. The exploded drawings are indispensable. Online fiche is cool, but greasy fingerprints on paper is much less annoying than on yr keyboard. And you'll have the original part numbers. Download one and print it out.

Gasket kits come with some o-rings, but not all. While you are in there replace the ones that don't.

Take lots of notes. Don't take any shortcuts.

[lucky]

find out the problem first I might do a compresion test an a leak down test on the motor to see if that is why it ran poorly to begin with. If it shifted through all 5 gears an didnt leak IMO i wouldnt crack the case
But if you do vesrah gaskit 100.00 seal kit 40.00 rings 100.00 hone 100 lapp valves 100 bearings 30-40 bucks
impact driver 10.00 vcb clutch plates an springs 45ish stainless bolt kit 40.00
get a good shop book, label an platic bag your parts use the right tools an ask questions an enjoy yourself.
Is this more than I should take on? thats up to you
paul

You cannot just take valves out and lap them. Once you take the valves out then you will see the hardened dried up valve guide seals and you need to replace those.
Then if you find out the valves wobble in the guides you cannot just put them back in and run it. You need to put in some new valve guides.

Either you rebuild the engine properly or you leave it alone.

Why not do it all? Then you have something of value.
Do you want it just half done? All clean and looking good but the engine is dirty and runs poorly,smokes etc.,. Remember it is 30 years old!! The engine really needs to come out of the bike and be inspected and some parts renewed.
If you do not want to do it then find a good shop to do it.
But do your homework do not just give the engine to anyone.

But just think how much a new motorcycle of the same size would cost these days.
They made more CB550's and cb750's than all new motorcycles combined. There are lots of parts.
The world is in a economic depression. This is the time to fix things.
We have more time than money.

[vaughnsmith]

My suggestion is to start with a compression test.  Warm up the bike for just a few min. then pull all the plugs.  Take a compression reading on each cylinder.   Remember to crank the bike with the throttle wide open and crank until the pressure stops going up.  Now go back and squirt a little oil into the spark plug hole and run a second compression test.  Not all compression testers read the same so the exact value is not as important as the  the reading from cylinder to cylinder and the difference between the "dry" and "wet" readings.  As an example on my #3 hole gives me 74 lbs. "dry" and 175lbs. wet.  That tells me 1. I have a compression problem and 2. its most likely the rings not the valves.

When I ride that bike the engine performance is very much "load related"  If I twist my right wrist hard in first, the engine pulls strongly up to about 7500 RPM  If I'm going a consent 55 mph and twist the right wrist I'll get a bad misfire.  If I slowly increase the throttle the bike will slowly run up to about as fast as I want  to go.

I know my bike needs rings, so in the near future I will be pulling the jugs and doing the "top end".  There is no reason to split the cases, so  I'll hone the cylinders and put in a new set of rings.  While I'm there, I"ll check the valves.  If they are showing any leaking, I'll pull all the valves, do a 3 angle valve job, replace the guides and seals.

I have a theory about bike,engine work... If your going to the effort and expense to go "this far" why not do it right?

[AEngelsrud]

Great advice all, thanks.

Question: can I do a compression test with a cold engine? It's not close to running but I could turn it over with the kick starter.

I do want to go this right and I want to learn more, so it seems like at least pulling the engine and doing a top end rebuild may be a good start.

Thanks again.

Aaron

[Brantley]

Question: can I do a compression test with a cold engine? It's not close to running but I could turn it over with the kick starter.

Yes, but expect slightly lower numbers (10%-ish?) cold. Kicking will also yield slightly lower numbers. But you should still get an idea of general engine health (like, if one cyl. WAY lower than the others). Even if the engine is out of the frame it's pretty easy to rig up a battery to make the starter do the work for you (make sure there's oil in it). If you have to kick it try to kick smoothly. Do each cyl. a bunch of times and average each.

[AEngelsrud]

Hello all!! I'm Back!!

I took a considerable amount of time off of this project to earn my Doctoral degree - that's done now so the bike comes back out! Woot!!

So, I've decided that I'm going to rebuild the engine and have fun with the process. I'm so glad to be back working on my bike again.

I've read back though this post - and my others - thanks so much for all the advice and guidance.  I'm sure I'll need a lot more.

Thanks!
Aaron

[Gman]

Welcome back!  Good luck w/the engine rebuild.  Post pics when you can...

Cheers,
G

[Sigop]

Btw, congrats on the doc, Doctor.

[bochnak]

Hey Doc,

Perform a compression and leak down test:

Top end rebuild if you need it:

[lrutt]

How many miles on the motor. If no leaks, ditto doing a proper tuneup. You really should run the motor a bit before checking compression. Checking on a motor that's been sitting won't be a reliable read.

If it aint broke....don't fix it.

[bochnak]

How many miles on the motor. If no leaks, ditto doing a proper tuneup. You really should run the motor a bit before checking compression. Checking on a motor that's been sitting won't be a reliable read.

If it aint broke....don't fix it.

I agree. If no leaks then they can run pretty good even with lower compression #'s.

[SOHC4 Cafe Racer Fan]

Just a brief, 5-year recess! Welcome back.  I'd do a compression test before tearing into it. Heck, I would advise trying to get it to run before tearing it apart.  It might just need a good tune AND (if you have a real winter where you live) you may want to enjoy the summer/fall riding season first.