Topic: CB650 - To rebuild bottom end or to not rebuild bottom end?

[ThePwninator]

Hi all

I'm removing the engine out of a CB650 -82 that i just purchased for repainting the frame and some other bits and bobs.
While the engine is out I will perform a rebuild of the top end but I'm not sure if it's worth it to dive deeper.

The bike is in so-so shape. I bought it as a no-runner that's been sitting unstarted in cold storage since -95 so I haven't had a chance to start her up yet (Carbs where a mess and the starter had rusted shut... Fixed now though!)

The engine turns and all that stuff and visual inspection into the engine looks ok to me. There is no visible oil leaks or damage to the engine. There is quite some aluminium corrosion built up on the casing though.

So, my question to the forum is this: Is it worth doing the bottom end while i have the engine out or should I save it for later? I feel its a bit of a monster task so wondering if there is a general consensus on when it's worth "diving in"?

Thanks for reading

/Johan

[Stev-o]

First off, welcome to the forum!

How many miles [or km] are on the bike?   So you bought it as a non-runner, guessing it "ran when parked"?!

Honda over engineered these bikes so as long as no water got inside the gear box, I would bet a little money that it is still fine.

Good Luck

[ThePwninator]

Hey! Thanks! 

it currently sits at 40000km so it has definitely moved around a little bit in its hay-day

The bike had been inherited by the neighbour of an older gentleman who had recently moved into a home so he had little info on the status of the bike other than that it had gone into the garage in 1995. It was also missing keys

the price was right though and i enjoy the challenge of getting it back into shape!

[BomberMann650]

Guess the leading question might be - are you comfortable working on cranks and transmissions?  Do you have the tooling to do it?

Fwiw - when i needed a newer motor for mine.  I just made sure the con rods weren't hosed and the transmission shifted before putting the top end together.

[fizzlebottom]

I considered doing the bottom end on mine a while ago. Crank bearings for the cb650 are nigh impossible to come by. And honestly, as long as it runs fine there's no reason to fiddle. If you're low on compression then do a ring job and take the opportunity to button up the usual oil leak points. Otherwise maybe freshen up the exterior and enjoy.

[ThePwninator]

are you comfortable working on cranks and transmissions?  Do you have the tooling to do it?

mje.. i have done full engine rebuilds on 2 strokes and smaller dirt bikes but feel the scale of this one is a bit daunting. I suppose in a lot of ways it would be the same only more bolts to loose track of..

Leaning towards leaving it as is and just do the top end rebuild which i feel very comfortable doing!

Crank bearings for the cb650 are nigh impossible to come by.

Thanks for the heads up!

[ThePwninator]

Just bought the Athena full gasket set but will stop at doing the top end at this time. Have a feeling the other bits might come in handy later...

Thanks for the input

[DaveBarbier]

I also agree on leaving it alone. But once you get into the top end you’ll have a better idea of what’s in the bottom end.

Drop the oil pan and look for bits of steel or bearing material. You will fine sludge which is completely normal. And have a gander at the primary chain tensioner to see if it’s doing it’s job, too.

You may find this link helpful. It’s a full o-rings, seals, chains, etc. list with Honda factory part numbers. I made that list…oof, about five years ago now. http://forums.sohc4.net/index.php/topic,140833.msg1877156.html#msg1877156

Some other links in my signature might be of use too.

[flatlander]

if you don't notice any problem with the bottom end i'm with those who say don't touch it, it'll be safe to leave it as is. these bikes are generally over engineered, and especially the bottom end is bullet proof.

40k is not much. i know in the US bikes often run a lot less but in europe they clock this amount of km easily, and much more. in roughly 40 years of service that these bikes have that's about 10k a year which is not much. i bought my 550 with 38k on it and more then doubled the kms in the 7 years i had it. i did a lot of work on it, but nothing in the bottom end and still see no reason to touch it.

[ThePwninator]

I also agree on leaving it alone. But once you get into the top end you’ll have a better idea of what’s in the bottom end.

Drop the oil pan and look for bits of steel or bearing material. You will fine sludge which is completely normal. And have a gander at the primary chain tensioner to see if it’s doing it’s job, too.

You may find this link helpful. It’s a full o-rings, seals, chains, etc. list with Honda factory part numbers. I made that list…oof, about five years ago now. http://forums.sohc4.net/index.php/topic,140833.msg1877156.html#msg1877156

Some other links in my signature might be of use too.

oh wow, super useful! Thanks!!

i bought my 550 with 38k on it and more then doubled the kms in the 7 years i had it. i did a lot of work on it, but nothing in the bottom end and still see no reason to touch it.

Good info, thanks

[Stev-o]

Drop the oil pan and look for bits of steel or bearing material. You will fine sludge which is completely normal. And have a gander at the primary chain tensioner to see if it’s doing it’s job, too.

Dave has given you very good advice here.

Start a thread in the "Project Shop" area so we can follow along.

[kerryb]

While you have the oil pan open, try to get a look at the starter clutch.  Rumor has it they are a weak spot on an otherwise excellent motor.  On mine, the bolts holding it on backed out, damaging the rollers and the springs.  Good news is, a used one from a 125cc atc was a cheap, perfect fit and slid in w/o much trouble.  There is an excellent tutorial on making the repair on cb650.com

[ThePwninator]

Start a thread in the "Project Shop" area so we can follow along.

I'm not sure my skillset is good enough to compete there...

While you have the oil pan open, try to get a look at the starter clutch.  Rumor has it they are a weak spot on an otherwise excellent motor.  On mine, the bolts holding it on backed out, damaging the rollers and the springs.  Good news is, a used one from a 125cc atc was a cheap, perfect fit and slid in w/o much trouble.  There is an excellent tutorial on making the repair on cb650.com

Thanks! I will definitely do that

[Jimcg]

I'm not sure my skillset is good enough to compete there...

Haha, have a look at my project thread and you will change your mind. There are always people who appreciate other bike projects, so please do.

Welcome by the way!

/Jim

[ThePwninator]

I'm not sure my skillset is good enough to compete there...

Haha, have a look at my project thread and you will change your mind. There are always people who appreciate other bike projects, so please do.

Welcome by the way!

/Jim

Thanks! And also thanks for the encouragement

[flatlander]

the best thing is that you will learn an awful lot by people just peering over your shoulder and commenting. you'll get useful advice on things that you wouldn't even have thought of asking.