[SteveThackery]

I've had a look at the automatic decompressor.  I can see how the curved weight is flung outwards by centrifugal force, which rotates a pin with a flat side and a curved side on it.

What I don't understand is what holds the curved weight inwards against the centrifugal force.  I was expecting to see some kind of spring, the tension of which would determine the speed at which the weight flings outwards.  As it is, it looks like the weight could be flung outwards at even the slowest of engine speeds.

What am I missing?

[singhg5]

There is a spring at the base. I will dig a picture or video and post it.

Here we go.

[SteveThackery]

Ah, you are right, singhg5!  I've just seen an exploded diagram in the manual.  I didn't notice it.  Next time I'm inside that cover I'll check to make sure it's there and working.

Sorry to have wasted everyone's time with this.

By the way, it looks pretty brutal to me - it's such a steep-sided little bump it must give the cam follower a heck of a thump as it passed beneath.  Does anyone know of other auto-decompressors and how they work?  I had a Honda-engined lawnmower with one, but that was virtually silent, with none of the horrible "clacking" our makes.

I wonder how much harm would come from removing it altogether.  Any thoughts?  Anyone done it?

[singhg5]

Ah, you are right, singhg5!  I've just seen an exploded diagram in the manual.  I didn't notice it.  Next time I'm inside that cover I'll check to make sure it's there and working.

Sorry to have wasted everyone's time with this.

By the way, it looks pretty brutal to me - it's such a steep-sided little bump it must give the cam follower a heck of a thump as it passed beneath.  Does anyone know of other auto-decompressors and how they work?  I had a Honda-engined lawnmower with one, but that was virtually silent, with none of the horrible "clacking" our makes.

I wonder how much harm would come from removing it altogether.  Any thoughts?  Anyone done it?

Yes, it has been removed in a few bikes. There seems to be no real issue except that they do not have the function of decompression, if they want it.   

[SteveThackery]

Yes, it has been removed in a few bikes. There seems to be no real issue except that they do not have the function of decompression, if they want it.

That's interesting.  My Electra X started just fine on the button, without using the decompressor (I never used the decompressor as it was disconnected).  As it's the same compression ratio as the UCE, I would think the UCE starter should cope equally well.

Presumably, when the mechanism is removed, that little flat-sided pin will have to remain in situ so the roller on the bottom of the cam follower doesn't drop down into the gap left behind.  There would have to be some way of jamming it in the "flat" position when the rest of the mechanism has gone.  Can you recall how this was done?

[Arizoni]

Starting was only one part of the decision to put the auto-decompression design into the engine.

More importantly, it was installed to prevent the kickback of the crankshaft when the engine is shut off.
The kickback caused by the piston being blown back down the cylinder by the compression on the last stroke can cause the sprag clutch to lock up.
If this happens, the energy thru the sprag clutch into the starter gear train and starter motor can greatly overload the  sprags.

I think the success of the design is shown by the very low numbers of sprag clutch failures the  new UCE engines have had.

By the way, most owners who still have electric starters on their iron barrels and AVL's highly recommend using the decompression lever to kill the engine on those bikes for the same reason.  It seems to greatly increase the life of the electric starter system.

[gashousegorilla]

By the way, it looks pretty brutal to me - it's such a steep-sided little bump it must give the cam follower a heck of a thump as it passed beneath.  Does anyone know of other auto-decompressors and how they work?  I had a Honda-engined lawnmower with one, but that was virtually silent, with none of the horrible "clacking" our makes.

I wonder how much harm would come from removing it altogether.  Any thoughts?  Anyone done it?

 

That's interesting.  My Electra X started just fine on the button, without using the decompressor (I never used the decompressor as it was disconnected).  As it's the same compression ratio as the UCE, I would think the UCE starter should cope equally well.

Presumably, when the mechanism is removed, that little flat-sided pin will have to remain in situ so the roller on the bottom of the cam follower doesn't drop down into the gap left behind.  There would have to be some way of jamming it in the "flat" position when the rest of the mechanism has gone.  Can you recall how this was done?

   There are a lot of different designs out there... Briggs and Stratton .... Other bikes as well. Some of the ones I have seen work on the rocker arm, in overhead cam Engine's.  And I haven't seen one that works quite like this one. Where it operates directly on the wheel of the Hydraulic roller lifter.... yeah, I think it can give that wheel a good whack, if it is malfutioning and if it activated at higher RPM's.  That's a lot of instability in that very long valve train, and the lifter relies on stability.  The lifters  I have found, pump very easily, and have very slow bleed rate.

  As fare as removing it, and the slot that the pin resides in.  The  flat of the pin does not sit flush with the base circle, it is recessed a bit.  It can't be due to the normal wear that can develop on the cam. So it is down in there..removing it in that regard doesn't matter.  However, I have seen sharp edges develop on the edge of that slot, that may cause the pin to hang-up. And I have also seen a slight pot hole develop over that slot, where the lifters wheel falls into it and gives it a bit of a bump as it travels around the base circle... not good with a Hydraulic lifter in my opinion.

  I like the Idea of a de-comp, but I'm not crazy about THIS design. In particular because of the possible troubles that it can cause with the lifters.   And I have had them, and I have heard about others who have had them.   Needless to say, mine is long gone.  The trench filled on the base circle, solid lifters used and I couldn't be happier.  As fare as the sprag goes?  Well my first  " WEAK" spag lasted 3 year with a ridiculous amount of E starts testing the mods I we did on my bike. And I'm? ... I guess around two years into the latest and greatest heavy duty up graded sprag.  No problems so fare.   I personally think the best thing you can do for your sprag, is to have a well tuned bike , that starts when you hit the button.  And of course a well charged Battery.

[Kevin Mahoney]

The design of the decompressor is an old one and may have been used by Briggs and Stratton in the past. The pros and cons are being grossly over thought here in terms of any ill effect. The only con to it is that it can be noisy. To run silently the flyweight and opposing spring tension have to be perfectly matched which is pretty tough. On the other hand with proper idle speed you will never hear it.

It was added to put less strain on the sprag clutch and for that reason alone. It is said to put 50% less stress on the sprag. Beyond that there is not ill effect from removing it nor is there an ill effect from leaving it. The bike we had in Bonneville was running at 12.5:1  and 225 lbs. compression with no sprag issues (probably 11.5:1 at that altitude).

As someone pointed out the decompressor in the AVL engines was all but useless and things worked fine.

[pmanaz1973]

Found this picture posted earlier by Kevin- makes sense once you see it like this.

[Kevin Mahoney]

I must have posted that in 1973.

[SteveThackery]

 
Needless to say, mine is long gone.  The trench filled on the base circle, solid lifters used and I couldn't be happier.

GHG, have you any idea why there is still a substantial amount of clickety tappet noise with these hydraulic lifters?  Mine are clearly audible, as are the ones I've heard on some of the videos.  I find this amazing: the hydraulic tappets on every car I've owned are always silent.  I was disappointed to find that the hydraulic tappets on the B5 make more noise than the solids on my AVL.  Any ideas why?

[ace.cafe]

GHG, have you any idea why there is still a substantial amount of clickety tappet noise with these hydraulic lifters?  Mine are clearly audible, as are the ones I've heard on some of the videos.  I find this amazing: the hydraulic tappets on every car I've owned are always silent.  I was disappointed to find that the hydraulic tappets on the B5 make more noise than the solids on my AVL.  Any ideas why?

Take off the tappet cover when hot after a ride, and see if ther is any up/down play in the pushrods. If the pushrods are not pre-loaded far enough into the lifters, then the vertical thermal expansion of the engine castings might be enough to cause some clatter. It could be possible that production variations of parts might allow this to happen on some bikes.

[gashousegorilla]

GHG, have you any idea why there is still a substantial amount of clickety tappet noise with these hydraulic lifters?  Mine are clearly audible, as are the ones I've heard on some of the videos.  I find this amazing: the hydraulic tappets on every car I've owned are always silent.  I was disappointed to find that the hydraulic tappets on the B5 make more noise than the solids on my AVL.  Any ideas why?

  Well, as you can guess, I'm not impressed with these lifters.  Thermal expansion does play a roll I think.... the use of aluminum rods as an example in an attempt to match the " Growth" of the head as it heats.  However, I have tried using adjustable rods with these lifter.... pre-loading to the center of the plunger travel.... No  better in my case. I still had lifter pump on occasion, verified with leak down tests... and burnt valve's and seats.

  I would pull your rocker covers's. Bring the engine to TDC on the compression stroke..... Lifters on the base circle's. And see if you have any down word push on the rod at the rocker arm.  If not ?.... give it a half hour and see if they bled down... If not ?   Check it tomorrow and see if they bled down.....

[ace.cafe]

Lifter pump can result from instability of the valve spring package too.
If the valve spring goes into a harmonic oscillation, or anything happens to make the valve spring lose control of the valve, the lifter will pump up to take up the room. And that, is when the burnt valve seats and such will happen. If the lifter takes hours/days to bleed down, then that also can make the problem much longer lasting, which means worse damage resulting.
While hydraulic lifters are known to have pump issues at high rpms, they are generally okay until higher than 6000 rpm and maybe up to 7000 rpm, PROVIDING that the valve spring package is giving good control.
If the pre-load is sufficiently deep to avoid any thermal expansion problems of excess lash occurring, then the primary cause of any pumping-up of the lifters would be loss of valve spring control over the valves.
Knowing what Enfield valve springs are like, especially since it is well known that the AVL had valve control problems at 5800 rpm, and the UCE valve springs are VERY similar(maybe identical) to the AVL valve springs, that might be where the pump up problem lies.

We always use our ACE proprietary valve spring package on all our heads, to avoid issues like this cropping up. Valves get out of control on solid lifters too, if the springs are lacking, but it doesn't cause the lifters to pump up.

We have resources to work some mods on the hydraulic lifters to solve various pump-up/bleed-down issues they may have, if that becomes necessary.

[gashousegorilla]

 Yup... been there and done all that.   The stock springs are good to around 5500-5800 WITH solids. Before it starts to blow out of the intake. If your reving that high.  Above that range you need to go heaver... or a Beehive.

 With THESE Hydraulics ?..... not for me.   Anti-pump Lifters ?.... perhaps. They will help with thermal expansion. But then again, your going to need an adjustable rod to set the proper pre-load, or at least a rod length checker. Then order rods for the proper length ?  But why when you could just use adjustable rods !    He...he..he.  For me, personally. Solid lifter's and adjustable rods work very nice...