REBUILDING A 79 ENGINE


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herdygerdy
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Re: REBUILDING A 79 ENGINE

Post by herdygerdy »

If you are in New Zealand and need replacement cam chains or tensioners for the CBX, contact this guy - brentmopar@xtra.co.nz. He's in Auckland.

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

Yep, I can do that with my trusty micrometer......
I went thru my buddy's inventory yesterday and he has about 6 complete sets so Im sure I can find a complete correct set to suit.
I noticed the cams are identified with [as an example] INL L or INL R and then a number '2' or '3' stamped on them. My cams all had '3' so I got only cams with '3' on them and Im hopeful I have the right ones as its -32 here this week and Im not keen to go back into his unheated shed again.
Thanks for the input.
Al

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Re: REBUILDING A 79 ENGINE

Post by daves79x »

Or the shop manuals give the actual lobe heights of each year cams.

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Re: REBUILDING A 79 ENGINE

Post by EMS »

Be careful with the shop manual numbers. In some versions of the 1980 addendum, the lobe heights are wrong. They show a intake lobe height of 37.8 -37.06 with a service limit of 37.7 ,which does not make sense, and which is a higher number than for the 1979. Similar is true for the Exhaust as listed with a height of 37.80-37.16
I found these values useless when checking cams.

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Re: REBUILDING A 79 ENGINE

Post by daves79x »

Relatively, they will tell you which year cams you have. Yes, there is a misprint, but it is so far off you can easily extrapolate what it should be. I have all the correct lobe heights written down somewhere and have posted them here several times.

Dave

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

OK, I think I have the correct cams, but the next issue relates to the main camchain.
We have installed the cams, torqued the head and slacked off the camchain adjuster, but the camchain is as tight as a banjo string......
The chain was purchased from our esteemed Florida supplier and its shown at 120 links on the packaging.....
Just how tight should the chain be, please help with guidance/advice.....????
Al

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Re: REBUILDING A 79 ENGINE

Post by daves79x »

I assume you mean the long vertical cam chain? Are you sure you pulled the tensioner all the way up to max slack? It can be sticky. That said, and it's too late now, but there is a spec in the shop manual for the chain length. I do not know off-hand the number of pins.

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

Yes its the main chain Im referring to. Im meeting with my engineer buddy at his heated garage today to review the engine as it sits with the tight camchain. It surely has to be related to the tensioner.......there's no other explanation.
Al

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

Anyone else have any suggestions to consider? I guess my biggest issue is I don’t know what is normal tension on these hyvo type chains when new.
Al

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Re: REBUILDING A 79 ENGINE

Post by herdygerdy »

Assuming you are using OEM tensioners, then the correct procedure is as follows:

1. Loosen off the chrome 10mm dome nut on the back of the cylinders (it has a copper sealing washer under it).
2. Then, using a pair of multigrips, pull UP on the round topmost part of the (long) 'A' chain tensioner. The idea is to reduce the amount of spring-loaded bow in the blade that is pushing against the back-side of the long camchain.
3. While holding the tensioner in the UP position, nip up that 10mm dome nut to hold the tensioner in that position.
4. Remove the RH end cap from the RH end of the crankshaft.
5. Using a 17mm spanner on the end of the crankshaft, put FWD (clockwise) rotational pressure on the crankshaft. This puts all load on the FRONT run of the long A camchain as the crank attempts to pull down on the camshaft sprockets. This also moves ALL slack in the camchain to the BACK run of the camchain. If you gently rotate the crankshaft fwd and back a few degrees, looking down into the camchain tunnel, you will see the cam chain slack 'swap' from front to back.
6. While holding that FORWARD rotational pressure on the end of the crankshaft, undo the 10mm dome nut. You should/may see/hear the camchain tensioner 'click' down and take up all the slack in the back of the chain as the spring in the tensioner pulls down and increases the bow in the slipper blade, forcing it against the back of the chain.
7. Sometimes the tensioners can bind up and not tension the chain correctly. Using your thumb, you can always give a firm push down on the top of the tensioner to take up the slack and then tighten the locknut.
Let us know how you get on.

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

hi herdy......
My problem is its a new camchain and it seems too tight, although the supplier says thats normal for the first few hundred miles.
We have the tensioner fully retracted and it could run as -is as the chain is quite tight, although we will release the tensioner before starting the engine.
I have done cam chain tensioning many times before so have no problem with the process, rather this is all about a new install that just doesnt appear to be quite right.
But thanks for the reminder......
Al

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Re: REBUILDING A 79 ENGINE

Post by daves79x »

The only answer to your question is something you don't want to hear or do - pull the chain out and measure it and compare to the original. Even a new correct chain should have a lot of slack with the tensioner pulled completely up and locked. That's the only choice you have and it's not an easy one.

Dave

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

yep, I dont wanna hear that but it seems to be the logical thing to do.
Thanks
Al

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Re: REBUILDING A 79 ENGINE

Post by herdygerdy »

OK Al, that's good that you are famil. with the process. The critical measurement that determines the degree of tightness of the camchain is the distance between the centre-lines of the exhaust camshaft and the crankshaft. Thick head and base gaskets add length to that measurement, decking the head, barrels or crankcase will reduce it.
The fact you managed to get the camchain on is a positive thing and I'd be tempted to run it as is, but be sure pull the camcover off again in about 500 kms to see how things are working out. Also use that opportunity to re-torque the head, drop the oilpan to check for, er, 'alien bodies' and to clean all your lint out of the strainer left in the engine from the cloths/rags used during assembly (you'll be amazed how much makes its way down there) and change the oil. Re-torquing the head may also reduce the tightness of the camchain by 'a bee's willy'. TBH, I'd be fairly confident your chain will settle in nicely as is. Others feel free to chime in...

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Re: REBUILDING A 79 ENGINE

Post by itsacbx »

Thanks Herdy,
Yes after sitting here gnashing our teeth for a few days and triple checking everything and talking to Preston Marks and a local CBX engineer/mechanic we have decided to button 'er up and move forward.
While the chain is tighter than Im normally used to with CB750's, Im sure it will settle in nicely, quickly.
Im shipping the engine to New Zealand and Im going to install it in my 79 and follow all your recommended protocols after about 500 km, then Ill decide whether to leave it in the bike or reinstall the 80 engine, whichever is the better of the two - [compression test etc etc]. Given how much Ive poured into this bike in cold hard Canuckbucks it will likely be this engine, but stranger things have happened in my Universe this year.
And all this assumes I can get my quarantine Voucher to actually get into NZ.
Thanks again.
Al

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