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koolio said:
Right, does anyone have any idea how you shift a frozen valve adjuster screw? ;)

I've managed to get the lock nut off, but the screw is completely rusted locked, I've applied ACF-50/penetrating oil and tapped with a hammer. May pull out the blow torch tomorrow.

Also one of the valves adjuster screws has rusted together with the lock nut, so adjustment is with the lock nut only, I'm afraid of trying to rotate the lock nut more to open as it drags the valve adjuster with it.

For future readers, you can just throw a box end wrench on the locknut. then use a screw driver to hold the adjuster screw in place.
then use a hammer to tap on the open end of the box end wrench until it pops. (just had to free mine on two of my 3 cb450 engines)
 

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Howdy,

I have a '74 CB450 and I have been trouble shooting poor compression and poor performance. (Bike wont go over 50mph). I previously set the points timing -- I set the valves at TDC with a .0015 gauge as previously discussed, buttoned everything up and went to kick it over tonight. The bike was banging and jumping on the center stand trying to hold idle. Freaked me out... A lot.

When I first adjusted the valves, they could be wiggled, letting me know I was TDC. Knowing that small clearance adjustments can really affect performance, I am confused.

Can someone recommend a set of double check instructions because this is very wrong and I need my bike back :(

Thanks all and stoked to have found this forum!
 

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Welcome! We appreciate a posting up in the introduction section with pictures, all the guys like pictures of these old beasts.

The valve adjustment is a PAIN on these bikes for sure, it sounds like you might have set them in the wrong spot, TDC happens twice in 4 cycles, and if you set them on the TOP of the exhaust stroke you might have set them considerably loose.

AS a test I like to just use the next FULL size gauge up from the one you are using to set clearance. See if it will go back in under the cam, without pushing the valve open. IF it does you are still too loose, if it doesn't you should be right.

Because there is so many parts flying around in these engines I set the clearance and then spin the engine over several times and then check them ALL again. Its also a good idea to set the cam chain tension BEFORE you set the valves. Its also a good idea to pull the cam tensioner OFF and make sure it is working properly, then reinstall it with the plunger all the way in so when you loosen the lock bolt you will hear it POP back out.

Feel free to post up about your other issues, there's plenty of knowledge floating around here. :lol:
 

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Sir Sherwood said:
Howdy,

I have a '74 CB450 and I have been trouble shooting poor compression and poor performance. (Bike wont go over 50mph). I previously set the points timing -- I set the valves at TDC with a .0015 gauge as previously discussed, buttoned everything up and went to kick it over tonight. The bike was banging and jumping on the center stand trying to hold idle. Freaked me out... A lot.

When I first adjusted the valves, they could be wiggled, letting me know I was TDC. Knowing that small clearance adjustments can really affect performance, I am confused.

Can someone recommend a set of double check instructions because this is very wrong and I need my bike back :(

Thanks all and stoked to have found this forum!
You need to make sure you are at TDC on the compression stroke. See my thread:
viewtopic.php?p=166063#p166063

Here are some tips to know you're at the right spot:

There are these ways I've learned to find if you're on the compression stroke at TDC:

1) Start moving the crank counter-clockwise. Put your finger over the spark plug hole. When you start to feel a "push", then you are nearing where you need to be (which is going to be "LT" if you're doing the left cylinder or "T" if you're doing the right cylinder. The "LT" indication of the crank will "fall" when it's in the compression stroke, and I've been backing it up clockwise and holding it there. For the "T" indication, it stays put.

2) You should see the lobes face out on the cam if you're in the right spot.

3) You should be able to wiggle the rocker mechanism with your finger when you're in the right spot.

4) You should see the intake valve start to close if you choose to not put your finger over the spark plug hole and see that the piston moving to the top. This is an indication that you're close.

5) Having mechanic friends watch over you also helps, but they confirmed that I am at TDC in the compression stroke, so my methods mentioned must be accurate.
 

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Thanks for the tips y'all!

I followed procedure to an (L) T on this valve tune and wondering 2 things...

1.) Was there enough clearance (wiggle) on the lobes when I was finally tightened down.

2.) Is my cam chain tensioner shot.

I am going to be digging in this weekend again. A friend told me that sometime the top cog for the cam chain can be one tooth out of place and throw it off. And being that there is play naturally on that cog, it can tricky(er)

Will update as soon as I turn over again! Thanks!
 

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If you are concerned about the cam chain tensioner, take the tensioner off and inspect it.

The push rod should move freely and the wheel toothed. It's worth stripping it down if it feels sticky at all.
When you come to replace it,compress the spring and lock down the shaft with the bolt, Insert it land when you have got a little tension on the front section of the can chain the release the bolt you will hear it snick into place. It will be correctly tensioned now.
 

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The bike is fully reassembled, however is still producing the same low power and compression :?

The bike is revving super RPMs in the first few gears. I checked the intake manifold for leaks or bad seals with a can of WD40 and there was no surge in the RPMs...

Backtracking to when I first got the bike. I am in Colorado so I rejetted the Mikuni VM32s for the altitude. I lowered the main jet size to mix with lower air value and have the needle jet in the middle (of 5) grooves. Could there be another adjustment that I am missing that is causing the high revving and poor performance right in the carbs?!

If there is not something more readily identifiable as the problem, I am thinking this is a top end rebuild :? Am I missing something obvious? A noob mistake?


Thanks all!
 

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just run a compression test before jumping to conclusions.
I'm told min. spec. is 163 PSI per side. HOWEVER, right before I needed a top end tear down my bike magically started with ease despite having far lower compression numbers. Yes, a mystery to us all.... :lol:

sometimes all that's in order is new rings and re-adjusting timing, carbs, etc. Or in my case....a new rocker arm, cylinder boring and honing, new pistons, rings, etc. But hey, now I'm happy.

how did it run before you noticed a difference?
 

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I ran another compression test today and its reading between 120-125psi on both sides. I knew compression was low so now I am thinking that this is deserving of a top end rebuild :roll:

Can't say I didn't anticipate this from the start...
 

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Thats a definite sadly but it will be worth it. However before you do that.
Was the throttle and choke wide open?
Was the engine at operating temp
Did the compression change after you put some oil down into the barrel?
If it is a yes to all these then its a top end rebuild. If not your valves may need adjusting. And if that does not cure then you will still need to take off the head to inspect the valves.
 

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can someone local do you a solid and properly adjust the valves? Look around and see. Then check compression again.
could it be something as simple as a tight valve compromising the compression readings?

if it's worst case scenario and it's top end teardown don't panic, like I did :roll:
take your time to find a buddy or a trustworthy wrencher to help. If it requires the work I previously described your bike will def. run better, I guarantee it. I basically state I have a classic bike with an almost new (?) motor; pistons, rings, boring, etc.

Even if you pay some $ you'll be better off than buying another 450 because upon completing the work you will know exactly what was done and how, as opposed to the mystery of bringing another bike home.

continue posting, these guys know what's up and have been a valuable resource to me.
 

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MIGHT just need the valve seats recut/lapped and or new rings. Bikes that sit a long time will have valves and valves seats that rust and end up not sealing. Rings get stuck in the grooves on the pistons and don't want to do their job. A simple tear down of the top end with the manual and a caliper and inside micrometer will tell you a lot.

Has the bike been just sitting for a long time before you got it?

Side note, might be time to start another thread about this, don't all this info to clutter up this thread and get lost.
 

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Interested in what was said above, I thought I’d try it out on the CB450. I am just finishing the construction of a café racer and have pod filters that actually filter and don’t interfere with the vacuum ports of the stock carbs. The Main jet is 150. There is a 2 into 1 header and a cocktail shaker muffler on the exhaust.



I had set the tappets to .0015. It would occasionally race up on in rpm to 3.5k but not often and the bike felt like it had some power. Because of the increased rpm and what was said above, I felt that the tappets may be too tight. Today I re-set them to .002. I would have a hard time not being at a higher RPM and felt like there was no power. Clearly this engine wants the smaller gap. Or have I not considered something?
 

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An extra half a thousandths tappet clearance is not going to affect the way the engine revs up. If it affects anything it will maybe smooth out the idle a (tiny) bit. If it won't rev up, there's another problem you need to address. Make the usual checks for air leaks, plugged jets, weak spark etc.
 

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Leigh said:
Figured it out. It was unrelated as far as I can tell. The screws holding the points base-plate had become loose so my timing was way off. The plate was fairly loose and when I moved it with a screwdriver the idle came right back to normal. Re-timed it and set the points. It's running very nicely with the valve clearance at .002" Pretty quiet too. Thanks for the info on valve clearances, it was very helpful because the recommended clearance from honda at .0012" was freaking me out. Sooooo thin!

Some observations from a first-timer on this 1971 cb450 valve adjustment:

The valves on my bike were set so that the leg of the "T" on the adjustment for 2 of the cam followers was pointed toward the spark plug instead of away from it when I started the valve adjustment. The cam lobes nearest the backwards "T"s had more wear than the others. Coincidental? Probably not. I simply loosened the lock-nut on the outside of the cam follower and was able to turn it around in the proper direction. I went very slowly and felt resistance when I went the wrong direction then turned it the other way and it all went fine. The adjustment could still be made when the "T" was turned around and facing the proper direction. No biggie. Setting the gap took some time to get the knack for tightening the lock-nut while maintaining the proper gap. Trial and error. It helped a lot to have the lock-nut already a little bit snug instead of loose when doing the adjustment because the adjustment kept changing when I tightened the lock-nut. Took the vacuum cylinder and vacuum piston off of the carbs to get better access to the intake-side valve cover but left the carbs on the bike.
This is nearly identical to how I did my procedure, with the exception to the perpendicular marks on the cam follower shaft, thankfully all four of mine were pointing away from the spark plugs. I noticed 3 out of 4 valves had larger than .003" of gap, fairly large, and probably the culprit of a noisy head. I went with the recommendations of others on this forum and set to .002–.0025".

It took me a couple of tries to get the adjustment to hold after tightening the lock nut. It only took experiencing this on one valve to learn.

After everything was buttoned back up I kicked her over and I too noticed a racing-idle, it screamed beyond 4k and I killed it.

I'm thinking the possibilities of this can be reduced to:

1. I didn't adjust the valves in the right position, and they are tighter than what the gauge said (.0025"), perhaps I wasn't aligned to LT, and was on LF when I did the adjustment. Is this even possible? I'm 99.9% sure I was LTDC on comp-stroke.

2. I failed to re-adjust timing after the valve-adj was made, meaning that timing was set to whatever spec the valves were previously at (much larger than spec).

3. The carburetor idle screws were set prior to valve-adj, and may have been turned too far

After noticing this, I went and re-timed to proper specs and adjusted both idle screws on the carbs. The bike runs pretty good, but the right side plug shows slight fouling and I'm getting some intermittent backfiring, and sometimes the bike will just die during idle.

Any ideas? Perhaps I should go through the entire process again just to be 100% sure?

Idle
 

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mike in idaho said:
An extra half a thousandths tappet clearance is not going to affect the way the engine revs up. If it affects anything it will maybe smooth out the idle a (tiny) bit. If it won't rev up, there's another problem you need to address. Make the usual checks for air leaks, plugged jets, weak spark etc.
I have a strong belief that there is a leak in the carb boot. will replace and see what current tappet clearance is like then.

Week spark revs an engine up?
 

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Replaced boots, random reving is fixed. still some other carb difficulties that will get worked out.
 

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we just went on a successful shakedown ride on one of our cb450s. fun to ride around on a cool night with my son...making lots of noise (straight pipes).

I'm hearing a lot of "ticking" on the left cylinder, and blowing flames out of the short pipes. I think I need to revisit the valve adjustment. we tried it once, but may not have gotten it right. does this make sense?

thanks to all you guys who have helped this rookie get a bike on the road.
 
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