Author Topic: How does AVL decompression cam lift the valve?  (Read 8573 times)

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StillCrazy

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on: November 23, 2017, 02:46:15 am
My 2009 AVL 500 Bullet has previously been stripped of its decompression cable. I am trying to restore decomposition capabilities, but the lever on the plate at the base of the valves does NOTHING. I have read where it is supposed to raise the exhaust valve, but a I can't find a drawing anywhere in either the shop manual (AVL Bullet Electra) nor the Snidal (admittedly classic iron cylinder) of HOW THE CAM LIFTS THE VALVE???  Obviously something is missing on my engine, but I can't finds drawing.

Thanks
Dennis
2009 AVL 500 Bullet, 1975 XL175


longstrokeclassic

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Reply #1 on: November 23, 2017, 07:23:21 am
Technically (in its stock form) it doesn't lift the exhaust valve at all. What it does is keep it open once it's been depressed by the exhaust cam.


tooseevee

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Reply #2 on: November 23, 2017, 01:40:01 pm
My 2009 AVL 500 Bullet has previously been stripped of its decompression cable. I am trying to restore decomposition capabilities, but the lever on the plate at the base of the valves does NOTHING. I have read where it is supposed to raise the exhaust valve, but a I can't find a drawing anywhere in either the shop manual (AVL Bullet Electra) nor the Snidal (admittedly classic iron cylinder) of HOW THE CAM LIFTS THE VALVE???  Obviously something is missing on my engine, but I can't finds drawing.

Thanks
Dennis

           Portis is correct. The AVL system does NOT lift the valve. It only holds the exhaust valve push rod UP once it has been raised by the rotation of the engine and the rising cam.

           I have removed it all, including the switchset lever, from my '08 AVL (it is virtually USEless except for killing the engine). Would it help you if I took pictures of the mechanism and posted them?

            Did YOU remove the mechanism or did someone else?

             Is the collar installed on your exhaust valve push rod?

             Addendum PS: The AVL compression release system doesn't help at all with kick starting if that is your goal. As Ace said, and I hesitated to do, it is a useless piece of shit (except for killing the engine). I kick start my engine just fine without any kind of compression release and it has 9.8:1 CR with horrendous strong Ace valve springs also.
« Last Edit: November 23, 2017, 03:31:55 pm by tooseevee »
RI USA '08 Black AVL Classic.9.8:1 ACEhead/manifold/canister. TM32/Open bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades.


ace.cafe

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Reply #3 on: November 23, 2017, 02:04:24 pm
In the common vernacular,  it is a piece of shit.

If you want a working decompressor,  it would be advised to install one of the small button-head decompressors in your head, like the Harley hotrodders use. This frees you up to use Bullet cams and better tappets if you plan to sort out the AVL properly.

We have done this on several models, and there should be some threads about it in the archives.
Adrian has a lot of experience with it too.
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StillCrazy

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Reply #4 on: November 23, 2017, 08:15:54 pm
Thanks for all your comments, always helpful.
The decompression cable and whatever else was removed by prior owner as well as: 1- the electric starter and 2- the original carb (Ucal CV BS29) which was replaced with Mikuni TM32. I found notes where he was trying to "richen" the original carb prior to changing to TM32.  All of which suggests he was having "kick-back" problems too.

I am only trying to restore the decompression capabilities so I can shut down the engine that way (as was suggested here as a way to reduce "kick back" on starting).  I also will try the Champion plug as suggested by 2cv (?) and not giving throttle as also suggested.

Here is a picture of what I have.

Thanks and Happy Thanksgiving to all!
2009 AVL 500 Bullet, 1975 XL175


tooseevee

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Reply #5 on: November 23, 2017, 10:59:49 pm
Thanks for all your comments, always helpful.
The decompression cable and whatever else was removed by prior owner as well as: 1- the electric starter and 2- the original carb (Ucal CV BS29) which was replaced with Mikuni TM32. I found notes where he was trying to "richen" the original carb prior to changing to TM32.  All of which suggests he was having "kick-back" problems too.

I am only trying to restore the decompression capabilities so I can shut down the engine that way (as was suggested here as a way to reduce "kick back" on starting).  I also will try the Champion plug as suggested by 2cv (?) and not giving throttle as also suggested.

Here is a picture of what I have.

Thanks and Happy Thanksgiving to all!

             As you will see from the picture of mine below, you are missing the collar on the exhaust push rod. Without it the cam has nothing to engage in order to hold the push rod up. The cam rotates to bear against the lip on the collar and hold it up. The collar is held in place by a teeny tiny #%^&^%^&**^%# circlip.
RI USA '08 Black AVL Classic.9.8:1 ACEhead/manifold/canister. TM32/Open bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades.


Adrian II

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Reply #6 on: November 23, 2017, 11:26:09 pm
I haven't fitted the small button head decompressor valve but I did fit the cast iron Bullet decompressor to my AVL hybrid engine's head, Mick Bailey did the same with his Electra-X. Using the C.I. Bullet decomp valve means you can operate the thing with a handlebar lever, either a classic chrome job or the plastic lever in the l/h switch cluster, details here:

https://forum.classicmotorworks.com/index.php/topic,25254.0.html

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


StillCrazy

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Reply #7 on: November 25, 2017, 04:58:37 am
Again thanks for the help.
While I really like the idea of a better decompression valve, and I will modify later, I need to solve the kick-back first. So I would like to restore the stock decompression system so I can shut down with that system.

Q: can I install a decompression collar without removing the head and lifting the valve? The service manual don't show enough detail for me to determine this. 

I'm sre this is an obvious question if you've had it apart, but I haven't and any guidance is appreciated.

Also it has been suggested that the tapper adjustment suggests a non-standard cam. Here is a picture of both tappets - do they suggest anything?

2009 AVL 500 Bullet, 1975 XL175


heloego

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Reply #8 on: November 25, 2017, 11:58:11 am
You won't need to pull the head.
Off with the tank (or lift it enough to access the exhaust rocker cover).
Remove the rocker cover.
Remove the oil line banjo bolt for the exhaust rocker, being careful you do not drop the rocker spring clip into the head.
Remove the exhaust rocker to free up the rod.
Install the decomp collar.
Remaining installation is the reverse of the above.

Guys? Did I miss anything?
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tooseevee

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Reply #9 on: November 25, 2017, 01:29:38 pm
           Your picture of the push rod adjusters wouldn't suggest that you have non-stock cams one way or another. Who gave you that idea?

           You would still adjust the free play in the same manner with both valves closed at TDC compression.

************************************************
StillCrazy,

         Since I wrote the above I've been thinking all morning about when I tried to install the special deep shrouded adjusters (and the modified collar) back in 2013 before I sent the head off to ACE.

          If I'm remembering correctly, you will not have any trouble installing an OEM collar if you have factory OEM adjusters. You can remove the adjuster, install the collar and circlip and reinstall the adjuster without prying up on the rocker arm or removing the rocker arm shaft.

          The problem arises with the special adjusters (they are longer) and the collar that goes with them (it is different than the stock one).

           The lifter must also have the groove for the circlip (which it probably does). When I bought my spare circlips from CMW in 2012 or '13 they were $3 and they are very fiddley.

            I might try installing these special adjusters again this Winter after some careful use of my Dremel tool and get rid of the collar at the same time.
« Last Edit: November 25, 2017, 05:05:29 pm by tooseevee »
RI USA '08 Black AVL Classic.9.8:1 ACEhead/manifold/canister. TM32/Open bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades.


ace.cafe

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Reply #10 on: November 25, 2017, 03:07:02 pm
Actually, if a previous owner put Bullet cams in it, the cam base circles are smaller, requiring longer pushrods.
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Bullet Whisperer

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Reply #11 on: November 25, 2017, 04:47:26 pm
           Your picture of the push rod adjusters wouldn't suggest that you have non-stock cams one way or another. Who gave you that idea?
 

             

                 
That was me, speaking from experience. It is possible to fit the earlier type Bullet cams, such as the 'S' cams, without changing the pushrods, but the adjusters have to be screwed about 2mm further out to compensate for the smaller base circle of cams such as those. The amount of threads exposed on those adjusters could suggest something like that has been done and the valve lifter collar being absent suggests the cam followers need to drop further than usual, perhaps to cams with smaller base circles.
 In the picture below, is 'Asbo' 11, an Electra X fitted with 'S' cams and standard pushrods. Both valves are closed, with the piston at TDC, the inlet cam retarded by 1 tooth. The adjusters on the pushrods are not screwed out very far because I also shortened the cylinder barrel by 2 mm and modified the piston crown to clear the squish areas on the cylinder head.
 B.W.
« Last Edit: November 25, 2017, 06:34:52 pm by Bullet Whisperer »


tooseevee

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Reply #12 on: November 25, 2017, 07:44:56 pm
That was me, speaking from experience. It is possible to fit the earlier type Bullet cams, such as the 'S' cams, without changing the pushrods, but the adjusters have to be screwed about 2mm further out to compensate for the smaller base circle of cams such as those. The amount of threads exposed on those adjusters could suggest something like that has been done and the valve lifter collar being absent suggests the cam followers need to drop further than usual, perhaps to cams with smaller base circles.
 In the picture below, is 'Asbo' 11, an Electra X fitted with 'S' cams and standard pushrods. Both valves are closed, with the piston at TDC, the inlet cam retarded by 1 tooth. The adjusters on the pushrods are not screwed out very far because I also shortened the cylinder barrel by 2 mm and modified the piston crown to clear the squish areas on the cylinder head.
 B.W.

           That explains it all as you usually do. I went down and looked at mine and I have about three exposed threads. That was what looked strange to me about StillCrazy's picture; so many exposed threads. Now I get it  :) :)
RI USA '08 Black AVL Classic.9.8:1 ACEhead/manifold/canister. TM32/Open bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades.


StillCrazy

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Reply #13 on: November 27, 2017, 08:36:38 pm
Thanks to each of you for your thoughtful comments and pictures - my learning curve is very steep and your patience is appreciated.  It would be easier if I were starting from stock but I find the challenge most engaging.

BW, when you say "...and the valve lifter collar being absent suggests the cam followers need to drop further than usual, perhaps to cams with smaller base circles." that would suggest that I can't install a new collar IF the cam has been changed, is that right? So, is there a definative measurement I can take to know OR can I just buy a collar and will it be obvious when I try to install it? 

Thanks,
Dennis



2009 AVL 500 Bullet, 1975 XL175


ace.cafe

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Reply #14 on: November 28, 2017, 12:41:53 pm
Not to horn in on BW's answer here, but yes you have it right.

And to add my 2 cents, I then you are better off to have the better cams than to restore that crappy decompressor. You might even be lucky enough to have a set of the S Cams that BW had made up a couple years ago.
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StillCrazy

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Reply #15 on: November 28, 2017, 06:46:19 pm
Ace - thanks.  So how can I know for sure which cams I have?  I was going to remodel the bathroom, but this sound like much more fun!
2009 AVL 500 Bullet, 1975 XL175


ace.cafe

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Reply #16 on: November 28, 2017, 10:26:02 pm
Ace - thanks.  So how can I know for sure which cams I have?  I was going to remodel the bathroom, but this sound like much more fun!
You can take off the timing cover and measure the cam base circles. That procedure is somewhat critical and complex, and I don't have the time right now to type the instructions.
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Reply #17 on: November 29, 2017, 06:22:08 am
You can take off the timing cover and measure the cam base circles. That procedure is somewhat critical and complex, and I don't have the time right now to type the instructions.

Hi Ace,

Will the magnum cams 'fit' the AVL motor? If yes, how/what will they contribute? i.e. how do you expect the motor to behave with the Ace Magnum cams in reference to power band, throttle response, torque, hp etc without any porting/valve work?

Thanks.


ace.cafe

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Reply #18 on: November 29, 2017, 06:47:10 am
Hi Ace,

Will the magnum cams 'fit' the AVL motor? If yes, how/what will they contribute? i.e. how do you expect the motor to behave with the Ace Magnum cams in reference to power band, throttle response, torque, hp etc without any porting/valve work?

Thanks.
Yes, they will fit and work in the AVL like other Bullet cams.

They will do basically what S Cams do, but also will give more torque, due to higher lift. They have similar timing specs to S Cams, but more lift.

We have not used them with stock AVL valve springs, and would recommend a valve spring improvement when fitting.

I don't have a dyno test of an AVL with these cams in it, but would expect probably low 30's for peak hp around 6000 rpm with a 32 or 34mm carb. The port is bigger than a stock Bullet.
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heloego

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Reply #19 on: November 29, 2017, 02:12:35 pm
Are the Magnum cams and springs still available?
Sounds like a nice addidtional project for me.
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ace.cafe

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Reply #20 on: November 29, 2017, 02:31:06 pm
Are the Magnum cams and springs still available?
Sounds like a nice addidtional project for me.
Yes, but I will have to order some. I don't have them in stock right now.
Please PM or email me for ordering details.
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Reply #21 on: November 30, 2017, 02:19:58 pm
Here is a dyno run for a pretty standard engine, with no porting work, shortened barrel and modified standard piston and 'S' cams. A VERY loud exhaust and 36mm MK 2 Amal were fitted  ;)