REBUILDING A 79 ENGINE


itsacbx
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REBUILDING A 79 ENGINE

Post by itsacbx »

Hey all, My 1979 CBX in New Zealand has an 80 engine installed and its using oil furiously, like I own Shell shares....
Id always planned to put the original engine back in and now the time has come to rebuild the 79 and do the swap. Ill sell the 80 engine as- is and use the cash to pay some of the costs of the rebuild.
The 79 engine is an unknown, and I know it will require major expenditures, based on the hack/chisel/saw marks along the bottom of the cylinders/head end caps/cases and much more butchery. Its one of the ugliest dismemberments of an engine Ive EVER seen.
So in a perfect world what parts should I upgrade, such as the Oldham coupling, drive shaft and so on? I already have a later clutch sitting in my boxes of parts. I also have a set of Viton valve seals.
Ill be re-ringing the bike at the very least and will add new pistins if needed, all chains, all gearbox bearings, mains and rod bearings, clutch plates etc.
Comments would be appreciated.
Lastly, where can I find the upgraded Oldham coupling sold in Europe please?
Pic of my bike with the 80 engine.
Thx
Al
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shiskowd
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Re: REBUILDING A 79 ENGINE

Post by shiskowd »

Al, I'm a newbie on the CBX engine but have dismantled 2 engines now and have read much as I plan my rebuild. If the '79 engine has any miles on it you'll likely need new valves with the proper seat work, maybe valve guides as well. Much has been documented about the low compression on these engines due to the soft valves. Common issue on the cylinders is pitting due to corrosion if they've been exposed to any moisture and/or wiped clean by fuel leaking form a carb - likely one of the contributors to your '80 engine using so much oil. New over standard pistons w/ re-bore to remedy. Cam tensioners are an issue but can be exchanged with the '80 engine should they be in better condition. Beyond those, measure the oil clearances on the cam, crank and rod bearings and compare to the service limits. Others with much more experience can pile on! :-)

You can buy the over-sized oldham couplings at SixCenter - https://www.sixcenter.nl/onderdelen/det ... 95&start=0
2010 KTM 690 Enduro Rally, 1979 CBX 'A' & 'B', 1975 Moto Guzzi 850T
Long Sleeping '79 CBX Restoration > viewtopic.php?f=102&t=11699

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Re: REBUILDING A 79 ENGINE

Post by EMS »

Here I am again, voicing my concerns about the oversize Oldham couplings. By design, these things are supposed to compensate for a radial offset between two rotating parts - here the cam halves. If the couplers do not slide freely between the two parts, there will be an undue radial load on them and the bearing supports - here the aluminum cam journals - will wear.
When the Danish CBX club came up with these oversize couplers 35 years ago, they supplied an instruction sheet on how to manually finish the couplers in order for them to slide freely when installing them. These instructions fell by the wayside, left out by those who stole the idea and sell the couplers for high $$$. Now, the "experts" recommend to freeze the couplers (thus shrinking them) for an easy installation. Guess what happens, when the engine heats them up again - they bind and your cam journals will go to the eternal hunting grounds.
This is just my opinion as a degreed engineer with some experience in applied Oldham connectors. You do whatever you want, and when someone tells you, they have used these that way on many, many bikes without a problem, go ahead and trust them.
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Re: REBUILDING A 79 ENGINE

Post by SIXHI »

"Id always planned to put the original engine back in and now the time has come to rebuild the 79 and do the swap"

itsacbx, good luck on the motor rebuild! That is a fun and a learning experience, just don't be in a hurry. Sorry the '80 is so thirsty for oil, my first red (used) '79 I picked up was like that. Didn't drip oil, and hardly smoked, but needed a pint or two a couple times a month.

For those interested in a direct swap motor replacement, I'll be selling a complete motor from a 1979, it was running fine and only had 11K on the clock when I pulled it out years ago. It was still running OEM carbs and exhaust at the time. It has been sitting in my living room for a decade and the missus has decided it is time for a proper coffee table instead of a CBX engine. I was the 3rd owner of that CBX, and only rode it a few times before pulling the stock motor and putting my race motor in, stock motor ran perfectly. Will probably put it up for sale in three or four months, have a few other priorities to tend to first.

Any suggestions about a fair market price for this motor and the best way to find a new home for it would be appreciated. Hopefully will go to an ICOA member or CBX enthusiast, I don't want to eBay it to just anybody.

jonb
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Re: REBUILDING A 79 ENGINE

Post by shiskowd »

EMS wrote:
Sun Aug 02, 2020 7:18 pm
Here I am again, voicing my concerns about the oversize Oldham couplings. By design, these things are supposed to compensate for a radial offset between two rotating parts - here the cam halves. If the couplers do not slide freely between the two parts, there will be an undue radial load on them and the bearing supports - here the aluminum cam journals - will wear.
When the Danish CBX club came up with these oversize couplers 35 years ago, they supplied an instruction sheet on how to manually finish the couplers in order for them to slide freely when installing them. These instructions fell by the wayside, left out by those who stole the idea and sell the couplers for high $$$. Now, the "experts" recommend to freeze the couplers (thus shrinking them) for an easy installation. Guess what happens, when the engine heats them up again - they bind and your cam journals will go to the eternal hunting grounds.
This is just my opinion as a degreed engineer with some experience in applied Oldham connectors. You do whatever you want, and when someone tells you, they have used these that way on many, many bikes without a problem, go ahead and trust them.
Mike - I've read your comments on other threads regarding the oversized oldhams. Makes sense to ensure the couplers are able to slide to manage any axial alignment imperfections. Otherwise Honda would have simply bolted the two cams tight to the chain sprocket. They must have anticipated slight twisting of the head during operation along its length. Are the oldhams unique to the CBX?

Found this on YouTube on oldham function - https://youtu.be/Y5lsvb_gq4o
2010 KTM 690 Enduro Rally, 1979 CBX 'A' & 'B', 1975 Moto Guzzi 850T
Long Sleeping '79 CBX Restoration > viewtopic.php?f=102&t=11699

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EMS
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Re: REBUILDING A 79 ENGINE

Post by EMS »

As far as the particular application as a cam connector, the Oldham couplers are unique to the CBX. Long cams and drive in the center, made it necessary to split the cams.
Oldham couplers as such are not unusual in applications where it is necessary to connect rotating parts that can incur a radial offset.
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Re: REBUILDING A 79 ENGINE

Post by Rick Pope »

So, just how much oil is this motor using? And under what conditions? It's not unusual for an air cooled engine to consume some oil when ridden hard.
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Re: REBUILDING A 79 ENGINE

Post by Larry Zimmer »

Feedback from one guy: oil consumption on my 82 is approx 1 quart for 750 miles of hard riding. Better at lower speeds/milder riding. Compression oood/ performance good. New viton seals. Might just need some new oil rings. Don't know. However, adding a quart of oil is much easier than a rebuild.
Based upon someone else's recent experience with boring, I'll add this comment: IF you do a rebore, be certain that whoever does it measures each piston and cuts matching bores accordingly. AND, that he gives your the cylinder block with each mating piston identified for its corresponding bore. That's how my Suzuki was done. After 40,000 miles it still used effectively no oil. (It is an air cooled.)
Larry Zimmer
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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

thanks for the input....I wont be replacing the oldham couplings as they are actually one of the few parts on the 79 pile of parts which appear to be decent and a good fit.
Salman [other poster] is helping me with the rebuild and we are going for a decent quality rebuild, at the best value, given the bike will only do a few thousand km each year. New rings/gaskets/all chains/80 clutch/all seals and only those parts which dont exceed specs.
Appreciate the help
Al

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

OK, rebuild is underway by Salman, with me providing the credit card to pay for everything.
Next question is what is the difference between a 79 and an 80 clutch?
My 80 engine in New Zealand rattles like a bastard and only eases up with putting pressure on the clutch such as pulling the lever in and easing it out slightly.......
Ive always assumed that the damper rubbers in that engine are due for replacement but given that Ive never been inside that engine I dont know what an 80 clutch looks like.
I also know that parts of the rattle is the alternator, but after paying for this rebuild, an optional alternator is out of the question, but Im going to buy the heavy duty spring that is for sale on various sites.

And last question is where do I buy parts for the 80 clutch? Tims? Randakks?

After an examination of the 79 engine its obvious that it was thrashed to death with few oil changes, and likely even fewer camchain adjustments.
The big end bearings were worn, one was gouged badly so they are being replaced.
Mains are being all replaced, as are chains, bearings and lots more.
Cases are being painted and damage to fins and the cases proper has been repaired.
Al

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Re: REBUILDING A 79 ENGINE

Post by NobleHops »

80 clutch has 9 dampers to the 6 of the 79. Is it better? Honda thought so. The cat’s ass is the spring-dampened 81-82 clutch. Sixcenter.nl has your service parts.
Nils Menten
Tucson, Arizona, USA '80 CBX, sort-of restored :-)

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

thanks Nils,
I will call my buddy Ted and see if he has a later clutch, otherwise Ill buy the service parts.
Thanks
Al

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

Next Question.....
Can someone tell me how many alignment dowels are in the engine. And Im told they are the solid type, not the sleeve type?
And Ive lost/misplaced my valve spring base washers - not the correct name but thats what I call them. Yes I should have 24 of those.......
Anyone have 24 to spare please?
Al

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

All sorted on the above matters, but my next question relates to cams....
Many of the lobes on my cams have the hard facing worn through, so Ive called on my buddy Ted again for replacements and he has lots, but how do we tell the 79 cam from the later ones?
Thanks
Al

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Re: REBUILDING A 79 ENGINE

Post by EMS »

You measure the cam lobe height. The lifts on the cams are different.
You try to get a reading of the base diameter - which may be a little difficult - and then measure the overall lobe height, The difference is the lift.
79 and 81/82 exhaust cams are the same, 7.5mm lift. 1980 exhaust cams have a lift of 7.0mm
1979 intake cams have a lift of 8.3mm, the highest of the 3 models
1980 intake cams are 7.8mm
1981/1982 intake cams are 80mm
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