Engine Rebuild
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- Posts: 98
- Joined: Tue Apr 30, 2013 8:54 pm
Engine Rebuild
I've never worked a bike engine before, so any advice would be great. I'm currently trying to get the engine off frame, and my clymer manual's in the mail. I have the carbs off and will look inside em tomorrow.
I've seen a few different kits out there, some with more parts to replace etc. I'll only replace what looks like crap, but as far as jets go, where can I pick up a better than stock set? I'm going to put strait filters to the intakes and eliminate the airbox.
Also, when I get to the pistons, what should I replace in there? I'm going to lap the valves, but should those and the springs be replaced? and what else?
I've seen a few different kits out there, some with more parts to replace etc. I'll only replace what looks like crap, but as far as jets go, where can I pick up a better than stock set? I'm going to put strait filters to the intakes and eliminate the airbox.
Also, when I get to the pistons, what should I replace in there? I'm going to lap the valves, but should those and the springs be replaced? and what else?
Re: Engine Rebuild
First, Your not experienced in tuning these engins So do your self a HUGE favor and stick with the stock air box. If you put stacks on the bike, you will run into al sorts of problems. Best to get everything right first, then if you still want to go to stacks, do it when you know the bike is running right and you are only chasing one problem.
I wouldn't do anything to the valves until you have the head off and do a leak down test. If you do end up doing valve work, make sure you replace the seals on the reassemble. On these engines, when you replace valve guides, you have to ream them to the correct size. I'm going to assume you are not set up for that, So don't open up that can of worms unless you have to Of course the "big" rebuild item is the pistons and rings. Here's where you run in to a real problem. Your not going to find overbore piston and rings short of a very expensive "big Bore" kit. Most will simply hone the bores and put the old pistons back with a new set of rings.
I would get one of the kits that have all the gaskets (including the head gasket) If you pull the head. Replace everything with new. to give you an example... I had a guy I met pull the head and only replace the head gasket. Well there are a couple of o-rings between the jug and head that he didn't replace. Soon after he put the bike back together he had the tell tale oil leak between the head and jug, That ment pulling the engine down again (and replacing the head gasket again) An expensive lesson in "replace everything".
I didn't see in this post which engin this was (year), but re building the carbs is your biggest step. DO NOT remove the carbs for the rack! Post the year you have so we can give you more recommendations. Or just buy my bike with the engine rebuilt right <BMFG>
Craig
I wouldn't do anything to the valves until you have the head off and do a leak down test. If you do end up doing valve work, make sure you replace the seals on the reassemble. On these engines, when you replace valve guides, you have to ream them to the correct size. I'm going to assume you are not set up for that, So don't open up that can of worms unless you have to Of course the "big" rebuild item is the pistons and rings. Here's where you run in to a real problem. Your not going to find overbore piston and rings short of a very expensive "big Bore" kit. Most will simply hone the bores and put the old pistons back with a new set of rings.
I would get one of the kits that have all the gaskets (including the head gasket) If you pull the head. Replace everything with new. to give you an example... I had a guy I met pull the head and only replace the head gasket. Well there are a couple of o-rings between the jug and head that he didn't replace. Soon after he put the bike back together he had the tell tale oil leak between the head and jug, That ment pulling the engine down again (and replacing the head gasket again) An expensive lesson in "replace everything".
I didn't see in this post which engin this was (year), but re building the carbs is your biggest step. DO NOT remove the carbs for the rack! Post the year you have so we can give you more recommendations. Or just buy my bike with the engine rebuilt right <BMFG>
Craig
Re: Engine Rebuild
OK, I did a little looking and you have an '82. That is good because you have screw in low speed jets which are easier to rebuild then the 81s.
Why don't you tell us a lot more about your bike, whats wrong with it, what you want to do to it. I would not even think of the brake change until you get it up and running. What condition is the engine in? Can you pot some pics?
We love projects, but we need to know a bit about what your working on and where you want to end up.
Craig
Why don't you tell us a lot more about your bike, whats wrong with it, what you want to do to it. I would not even think of the brake change until you get it up and running. What condition is the engine in? Can you pot some pics?
We love projects, but we need to know a bit about what your working on and where you want to end up.
Craig
Re: Engine Rebuild
Welcome here!
interesting username (it has a meaning in German)
My first question is why do you think you have to work on your engine at all?
One may replace the cam chain for precaution after say 45000mls and the valve stem seals in case of oil consumption, too. Beyond that, there is no necessary work if nothing is really damaged.
interesting username (it has a meaning in German)
My first question is why do you think you have to work on your engine at all?
One may replace the cam chain for precaution after say 45000mls and the valve stem seals in case of oil consumption, too. Beyond that, there is no necessary work if nothing is really damaged.
Cosky's great (free) online manual: http://cosky0.tripod.com
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
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- Posts: 98
- Joined: Tue Apr 30, 2013 8:54 pm
Re: Engine Rebuild
so... firstly its been sitting for 20 years strait. As is in the first pic. Just like so... for 20 years. Reg expired in 93. 24k miles i believe. There was a 750 i think, sitting next to it (which I plan to snag soon too). A bike engine cant be much different than any car engine I've worked with... anyways, I understand your concern, but that is what forums are for, as long as anyone's willing to teach, I'm more than willing to learn. I'd like to know more about this particular engine so I can tune it. But all im really concerned with is just ensuring integrity. That is what the project is all about to me. I love the build. I'm in no rush to get it on the road,. I just love the process of the restoration. I never planned on Not putting new seals in either. I would kill myself if i skipped that. I already ordered a complete engine gasket kit so far. I've yet to get to the pistons to really see if there's any problem. I've only lifted off the valve cover.
So far one of the carbs had a little build up, but the others were very clean. and I've only lifted off the valve cover as you can see in the photo. Very clean inside as well. The gaskets are in amazing shape if i may say so. Im still weary because there was a wimming pool n both exhausts leaving me to believe some maybe lots of moisture found its way into the block.
I plan on just replacing rings, lapping valves, repl valve bushings, all gaskets, honing barrels, painting pink unicorns on the pistons, rebuild the one bad carb... and thats about it. I hope you'll stay tuned cgswss, thanks for the look. Also, I may have to take them off the rail because the T lines snapped.
Volker, Thanks, I hope you can surmise why i'm looking in the block from my explanation above. The odometer claims to be at 24k, but I swore it said 37 when I rolled it in the garage. It may have been bumped....It wouldn't hurt to swap that as well.
dang, issues w/ uploading pictures to this post. ill try to add to my profile!!!!
So far one of the carbs had a little build up, but the others were very clean. and I've only lifted off the valve cover as you can see in the photo. Very clean inside as well. The gaskets are in amazing shape if i may say so. Im still weary because there was a wimming pool n both exhausts leaving me to believe some maybe lots of moisture found its way into the block.
I plan on just replacing rings, lapping valves, repl valve bushings, all gaskets, honing barrels, painting pink unicorns on the pistons, rebuild the one bad carb... and thats about it. I hope you'll stay tuned cgswss, thanks for the look. Also, I may have to take them off the rail because the T lines snapped.
Volker, Thanks, I hope you can surmise why i'm looking in the block from my explanation above. The odometer claims to be at 24k, but I swore it said 37 when I rolled it in the garage. It may have been bumped....It wouldn't hurt to swap that as well.
dang, issues w/ uploading pictures to this post. ill try to add to my profile!!!!
Re: Engine Rebuild
OK so to start, do you have the manuel yet?
[url]http://cosky0.tripod.com//url]
Now as you have the carbs off, and plan to split them, you should go here for some help.
[url]http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revD.pdf/url]. While I was doing it I chose to get the screw kit (SS cap screws to replace the junk screws that come with it.
This is VERY important! The screws that go threw the choke butterflies are NOT to be reused! When they are first put in they are split so they won't come back out under vibration. DO NOT put the old ones back in. Get 8 ( 3mm X .5 X 6mm ) socket-head Screws. Try to get Stainless grade A-2 (aka 18-8). When you reassemble the carbs clean the holes in the choke rod with Acetone just before installing the screws using RED loc-tite. (you will have to heat the screws up with a heat gun if you ever take the rack apart again)
When you first open up the float bowls, unscrew the low speed jets in drop them in a cup of Acetone to soak. Later you can use the little wand on the caned carb cleaner to blow then out. These jets should allow a strong stream from the carb cleaner when clean. I will bet you dollars to donuts that you will find at least one and most likely all of these will be clogged.
Replace ALL the float bowel gaskets and the float needles.
Very important to disassemble the #2 carb. Be very carful when removing the accelerator pump diaphragm. It is ultra important to make sure the passages under the diaphragm are clean and free flowing. I hope the diaphragm is still good. If they were not so hard to find, I would tell you to just replace the diaphragm on general principles.
OH, If the bike still has the vacuum shutoff attached to the carbs, get rid of it and plug the vacuum line.
I would also line up a set of the rubber connectors between the carbs and the head. I replace the clamps with new SS hose clams as well. The problem is finding some that are narrow enough
For rebuilding, I hope you have a torque wrench that you can go down to something like 6 or 7 ft lbs. You will need one. These engines have a whole lot of little bolts holding the head down instead of fewer large heavy studs you see on other engines. Also don't forget to get and use a small squeeze bottle assembly lube. I would also sugest you invest in a couple of thread chasers as I will bet you will find a couple of the head screws will have messed up threads.
I have build a LOT of overhead cam engines, so the removing the cam to get the cam chain free is a snap for me, but I'm betting this is will be a bit of a chore for you. believe me that once you remove those two screws, there is a way to slide that cam thru the timing gear- just take it slow and be careful turning the cam to get the lobes thru.
[url]http://cosky0.tripod.com//url]
Now as you have the carbs off, and plan to split them, you should go here for some help.
[url]http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revD.pdf/url]. While I was doing it I chose to get the screw kit (SS cap screws to replace the junk screws that come with it.
This is VERY important! The screws that go threw the choke butterflies are NOT to be reused! When they are first put in they are split so they won't come back out under vibration. DO NOT put the old ones back in. Get 8 ( 3mm X .5 X 6mm ) socket-head Screws. Try to get Stainless grade A-2 (aka 18-8). When you reassemble the carbs clean the holes in the choke rod with Acetone just before installing the screws using RED loc-tite. (you will have to heat the screws up with a heat gun if you ever take the rack apart again)
When you first open up the float bowls, unscrew the low speed jets in drop them in a cup of Acetone to soak. Later you can use the little wand on the caned carb cleaner to blow then out. These jets should allow a strong stream from the carb cleaner when clean. I will bet you dollars to donuts that you will find at least one and most likely all of these will be clogged.
Replace ALL the float bowel gaskets and the float needles.
Very important to disassemble the #2 carb. Be very carful when removing the accelerator pump diaphragm. It is ultra important to make sure the passages under the diaphragm are clean and free flowing. I hope the diaphragm is still good. If they were not so hard to find, I would tell you to just replace the diaphragm on general principles.
OH, If the bike still has the vacuum shutoff attached to the carbs, get rid of it and plug the vacuum line.
I would also line up a set of the rubber connectors between the carbs and the head. I replace the clamps with new SS hose clams as well. The problem is finding some that are narrow enough
For rebuilding, I hope you have a torque wrench that you can go down to something like 6 or 7 ft lbs. You will need one. These engines have a whole lot of little bolts holding the head down instead of fewer large heavy studs you see on other engines. Also don't forget to get and use a small squeeze bottle assembly lube. I would also sugest you invest in a couple of thread chasers as I will bet you will find a couple of the head screws will have messed up threads.
I have build a LOT of overhead cam engines, so the removing the cam to get the cam chain free is a snap for me, but I'm betting this is will be a bit of a chore for you. believe me that once you remove those two screws, there is a way to slide that cam thru the timing gear- just take it slow and be careful turning the cam to get the lobes thru.
Re: Engine Rebuild
Thanks for the pictures.
In fact this bike looks like it could need some extra care.
One thing to keep in mind: the threads are very susceptible! You need a small enough torque wrench (maximum range not higher than up to 40Nm) and urgently keep to the stepwise pattern e.g. for cylinder head and its cover.
If you still have the stock black cylinder bottom gasket, have fun during replacement! I spent hours (or days?) scratching it off.
In fact this bike looks like it could need some extra care.
salzig hund wrote: A bike engine cant be much different than any car engine I've worked with...
One thing to keep in mind: the threads are very susceptible! You need a small enough torque wrench (maximum range not higher than up to 40Nm) and urgently keep to the stepwise pattern e.g. for cylinder head and its cover.
If you still have the stock black cylinder bottom gasket, have fun during replacement! I spent hours (or days?) scratching it off.
Cosky's great (free) online manual: http://cosky0.tripod.com
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
-
- Posts: 98
- Joined: Tue Apr 30, 2013 8:54 pm
Re: Engine Rebuild
ALCON,
Just what I was looking for. You guys have added to my to do list already!! cgswss and volker, Thanks! If it wasn't for the nasty looking valve's, I'd really regreated taking it apart to begin with. So far, all of the gaskets have such amazing play, stretch.. Alas, new seals = better.
I've had no issues with turning bolts so far, vice the mounting bolt (hi rear). We'll see when I pull the block apart.
The hose clamps for carb boots were in fairly good shape, although, replacing w/ hex/flat heads would be ideal for a future removal.
I haven't touched the accl. pump. yet, its soaking over night and no vacuum shut off. Just three airlines going from the box to carb and Intake valve.
No, no manual yet. I'm away for a week so It should get there by next. I do have a respectable collection of mechanic tools, but I am away from home. AD USN in Ventura CA. All the good stuff is back in FL in storage.
Thanks again. Any more info don't hesitate to drop it in. I soak up all knowledge!
Just what I was looking for. You guys have added to my to do list already!! cgswss and volker, Thanks! If it wasn't for the nasty looking valve's, I'd really regreated taking it apart to begin with. So far, all of the gaskets have such amazing play, stretch.. Alas, new seals = better.
I've had no issues with turning bolts so far, vice the mounting bolt (hi rear). We'll see when I pull the block apart.
The hose clamps for carb boots were in fairly good shape, although, replacing w/ hex/flat heads would be ideal for a future removal.
I haven't touched the accl. pump. yet, its soaking over night and no vacuum shut off. Just three airlines going from the box to carb and Intake valve.
No, no manual yet. I'm away for a week so It should get there by next. I do have a respectable collection of mechanic tools, but I am away from home. AD USN in Ventura CA. All the good stuff is back in FL in storage.
Thanks again. Any more info don't hesitate to drop it in. I soak up all knowledge!
Re: Engine Rebuild
I can see this part on your first picture. Placed on the rear top of carbs 3+4.salzig hund wrote:... and no vacuum shut off. Just three airlines going from the box to carb and Intake valve.
Cosky's great (free) online manual: http://cosky0.tripod.com
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
Re: Engine Rebuild
You'll probably break at least one head bolt so you may as well try to find a set.
I've only rebuilt one CB650 motor so these guys will probably give you more help in that regard.
But
You'll probably need to do a lot of electrical work; judging by the corrosion on the engine, the connectors will be corroded and loose.
The factory charging system is relatively well-engineered for the era, though ~30 years and quite a few heat cycles will have quite probably toasted the regulator and/or field coil - this is a very common problem with these bikes. You'll want to measure the resistance across the slip rings on the field coil.
Resistance should be between 4 and 10 ohms. Many manuals say <1 ohm but this is, most assuredly, incorrect.
The resistance across all three stator wires (yellow) should be less than 1 ohm between each wire, with no continuity to ground.
If your field coil is shorted which is common, your regulator is probably burned out as well. Volker has a link to the manual in his signature that will show how to troubleshoot the regulator. HERE is a link directly to the VR Test page of the manual. Check the link in my signature for a cheap and effective replacement if yours is bad.
You'll probably want to get the bike running before doing any "upgrades" to minimize variables when troubleshooting, but if you want to upgrade your ignition the HEI conversion in my signature works very well.
I've only rebuilt one CB650 motor so these guys will probably give you more help in that regard.
But
You'll probably need to do a lot of electrical work; judging by the corrosion on the engine, the connectors will be corroded and loose.
The factory charging system is relatively well-engineered for the era, though ~30 years and quite a few heat cycles will have quite probably toasted the regulator and/or field coil - this is a very common problem with these bikes. You'll want to measure the resistance across the slip rings on the field coil.
Resistance should be between 4 and 10 ohms. Many manuals say <1 ohm but this is, most assuredly, incorrect.
The resistance across all three stator wires (yellow) should be less than 1 ohm between each wire, with no continuity to ground.
If your field coil is shorted which is common, your regulator is probably burned out as well. Volker has a link to the manual in his signature that will show how to troubleshoot the regulator. HERE is a link directly to the VR Test page of the manual. Check the link in my signature for a cheap and effective replacement if yours is bad.
You'll probably want to get the bike running before doing any "upgrades" to minimize variables when troubleshooting, but if you want to upgrade your ignition the HEI conversion in my signature works very well.
Last edited by Pinhead on Thu May 23, 2013 8:40 am, edited 1 time in total.
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- Posts: 98
- Joined: Tue Apr 30, 2013 8:54 pm
Re: Engine Rebuild
awesome. This has been the next headache ive yet to look into. I've just recently done some digging online, but this will help with ignition. The only variance will be the intake, but I want it to run with all original parts found then tweak from there. Pinhead, Thanks for reaching out!. Thanks all for looking!
Re: Engine Rebuild
I do need to get some pics/videos of the electrical mods I've done to my bike... I've told many people I would do it but haven't gotten around to it.
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- Posts: 98
- Joined: Tue Apr 30, 2013 8:54 pm
Re: Engine Rebuild
How bad are minor scratches on the rocker arms? You can barely see from the photos, but a few of the arms have taken a few nices scratches. Replace?
Re: Engine Rebuild
One bit of advice I recommend, as I'm currently helping rebuild a friend's '80 CB650:
1. Invest in a piston compressor.
2. Pay attention in the manual as to where the piston rings are to be positioned.
3. INVEST IN A MOTORCYCLE VALVE SPRING COMPRESSOR! I cannot begin to explain to you how much of a pain in the ass it is to try to put the valve retainers back in with an automotive valve spring compressor. It took a friend and I TWO hours to get through TWO springs; we're damn lucky we haven't lost any parts yet, after having them shoot off a few times.
4. If you know your stator is working fine, don't crack open the case. Supposedly, stator gaskets for the engine are hard to come by now, and the Athena gasket kits do not include a stator cover gasket.
5. This website is a GODSEND: http://www.jasonkent.ca/cb650manual.htm
1. Invest in a piston compressor.
2. Pay attention in the manual as to where the piston rings are to be positioned.
3. INVEST IN A MOTORCYCLE VALVE SPRING COMPRESSOR! I cannot begin to explain to you how much of a pain in the ass it is to try to put the valve retainers back in with an automotive valve spring compressor. It took a friend and I TWO hours to get through TWO springs; we're damn lucky we haven't lost any parts yet, after having them shoot off a few times.
4. If you know your stator is working fine, don't crack open the case. Supposedly, stator gaskets for the engine are hard to come by now, and the Athena gasket kits do not include a stator cover gasket.
5. This website is a GODSEND: http://www.jasonkent.ca/cb650manual.htm
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