Mushroom Head Tappet/Rocker Adjusters (2005)

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Mar 7, 2005
I have just had some work done on my 850 head (new exhaust valve & seats).

There is some pitting on one of the rocker adjusters. Now is the time to replace them if I am going to ride this Australian summer.

I see that you can get Mushroom Rocker Adjusters for Triumphs but I haven't found any listed for Nortons.

I also see reference to socket adjustment.

Without seeing the different types I'm not sure what way to go.

The mushroom head has a more even contact with the valve stem which will help reduce top end clatter.

Parts available in Canada at Walridge Motors for $ 40 set

Mushroom tappet adjusters for Nortons are available from Raber's Parts Mart in San Jose, California. However, I recommend their use only on the intake valves. There is an awkward angle between the exhaust valve and the rocker, which becomes quite ugly when mushroom adjusters are installed. You end up with point contact between the valve and mushroom, defeating the purpose of the larger adjuster.

Try- - US$ 28 plus shipping
Mushroom Head Tappet/Rocker Adjusters (2005)

I have a set, but have yet to install them - the business end of my adjusters look like a pitted moon surface, the threads are chewed up from over zealous locknut tightening and the locknuts have been mauled by a vise-grip gorilla. :shock: I turned down and polished the faces, but plan to install the 'shrooms this (Canadian) winter.

Jason - can you elaborate on the exhaust angle? Considering the mushroom head is a dome - isn't all contact between a dome and a plane, point contact?

Another nice photograph there Fastback!

As you say, technically there will be single point contact between a spherical surface (mushroom) and a flat surface (valve stem). In reality, wear will tend to match the two surfaces, resulting in a larger contact patch. And this larger contact patch is the perceived advantage behind using mushroom adjusters.

Now, the exhaust valve rockers, owing to their stubby length, appear to rotate on a shorter arc than the intake valves. Therefore, when the exhaust rocker begins to contact the valve stem, the adjuster is not perpendicular to the stem. This angle causes the adjuster to make contact on the edge of the valve stem, or nearly so.

For example, if you take the mushroom rocker that is standing up in your picture and pivot it 20 degrees to the table, it will give you a visual of what I’m attempting to describe. Next, with the adjuster at this angle look at where the mushroom head is contacting the table. The edge of the adjuster is making contact quite a distance away from its center. The larger mushroom head increases the angle of contact between the stem and valve. This larger angle causes the adjuster to contact the valve stem more toward its edge. Also, as the valve opens, the adjuster must rub from one edge of the valve stem to the other side (possible side loading, point loading and scuffing will occur).

The contact angle between the mushroom and valve stem is not as severe on the intake side. So, I use the mushroom adjusters on the intakes, but not the exhaust.

Jason, I think your way off on this. All rockers do this, start and finnish at an angle. The only time the adjusting bolt is inline with the valve is when it is right in the middle of it's travel. When setting up any changes to the valve train you adjust the push rod length to make sure that the contact area is symetrical on the diameter of the valve stem. These adjusters with radised tips simply prevent scuffing of the valve stem tip. It is up to the owner to select one that does not cause geometry problems. The ones in the picture do not, they are bolt on. But always should be checked. I have also used ones that were so large as to require grinding of the rocker and end caps for the stems. lots of extra work. norbsa
Thanks Jason -
I can visualize what you are saying, and it seems to make sense.
Would the geometry be improved if the diameter of the exhaust faces were reduced- that way you gain the benefits of the mushroom with less potential for sideloading.

I'll have to check it out when I pull the head off. Is there enough clearance to install the new tappets just by pulling the head off, or do I need to pull the spindles out too? My memory suggests that there will be enough space to come in from below without disassembly.

Thanks for the compliment on the photo, but I can't take credit- it is the pic on - now I'll have to take one myself. :wink:
This is from another board but fits in well.
Ol' 441
Member # 4049

posted October 23, 2005 11:53
After reading some discussion about pushrods I decided to add my 2 cents worth...

Of all things Pushrod:

Disclaimer: I am certainly no "expert" however I probably have much more experience in some of these matters than your average wrench twirler, having said that please feel completely free to take what I write with a grain of salt and also feel free to pick me apart if you care to do so...

Pushrod length is not critical however it is important to retain the correct valve train geometry to both increase performance and reduce valve guide wear...
The easiest way I have found to determine the correct pushrod length is to make an adjustable pushrod to use while setting up the engine... I used a standard steel pushrod with one end cut off an inch or so and brazed a nut to the top end of the now shortened pushrod,,, I installed a round head screw in the nut with a spring under the screw head to retain the adjustment of said screw... Now I adjusted the pushrod to the standard length required for my engine as a starting point... To make my life less complicated I installed a light spring on the valve I was checking and used a black marker pen to show me where the rocker arm was actually contacting the top of the valve stem... This done I assembled the pushrod/rocker arm assembly to the correct running clearance and turned the engine over a few times... Now my valve stem shows exactly where the rocker arm was contacting the valve stem by wearing away the color of the marking pen on the end of the valve stem... This wear pattern should be well centered on the valve stem tip, if the wear pattern is towards the rocker arm side of the valve stem the push rod is too short, if the opposite is true the push rod is too long for proper valve train geometry...
A pushrod length that is either too long or too short will have a tendency to push the valve stem towards or away from the center of the valve guide causing increased friction and accelerated wear...

Pushrod material: I believe the pushrods in my little B44 engine are made of an aluminum material with hardened steel inserts pressed into the ends but I haven't had the engine apart in so long that I can't be certain about this either <sigh> My guess would be that BSA used aluminum for the pushrod material to closer match the expansion rate of the aluminum cylinder there by retaining the valve clearance through a wide range of temperatures... This should be taken into consideration if a person were to replace the aluminum pushrods with those made of steel, the valve clearance will more than likely increase as the engine warms up to normal operating temps because of the lower expansion rate of the steel material... Steel has about 3 times the strength of aluminum and it is also about 3 times the weight of aluminum size for size so we really do have to determine which is the lesser of the two evils when contemplating a change in materials for this application...

I could go on but I don't care to bore anyone, I hope I have cleared up a wee bit of this mystery for at least one of our readers, if so this was time well spent...

Ol' 441

Ol' 441


The mushroom adjusters are bigger than stock adjusters. As such, their contact with the valve stem will be further off center than stock adjusters at any angle other than perpendicular. So, at the beginning of valve actuation, the adjuster will contact one side of the stem. It will then travel to the other side of the valve stem at the end of the valve actuation cycle. The bigger the adjuster the more this side-to-side scuffing will occur. This phenomenon is more pronounced on the exhaust side, owing to the smaller arc that the rocker travels through.


You do not need to pull the spindles in order to install the mushrooms. In fact, you may not even need to remove the head in order to install the adjusters (but don’t hold me to this). Smaller exhaust mushrooms will reduce side loading of the valve. However, this will also decrease the bearing area, putting you right back where you were with the stock adjusters. Install the mushrooms on the exhaust side and see what you think; you can always go back to stock.

Based on the input I think I will stick with the standard rocker adjusters. It wasn't noisy before so I will see what happens. It looks relatively easy to change the rocker adjusters in the future if needed.

I want to keep the appearance of the bike near standard but use superior parts where possible. The major exception to this is the front brake. I am reviewing the braking thread with interest.

I note that the term 'adjusting the tappets' is used when setting the rocker clearance. Is this technically correct? The tappets do not appear to have any adjustment capability.



850 MkIIa Interstate
I was in there the other day (under the valve covers) - the mushroom head adjusters need to come in from below as the mushroom won't fit through the hole in the rocker... I didn't check the intake, but no room on the exhaust. With everything in place - someting has to go - the question is both head or head and spindle...

As far as tappet adjuster vs. rocker adjuster - I guess rocker adjuster is correct but considering the gap has to do with the cam-to-valve-train - it is all the same... is it a tappet or cam follower... :wink:

If you remove the stock adjuster and disconnect the rocker from its pushrod, you can tilt the rocker WAY back. In fact, I believe it will tilt back far enough to install the mushroom adjuster from the bottom of the rocker; try it and let us know.

Thanks Jason,

I tried that but I couldn't get the pushrod out of the way to tilt the rocker arm back.
No big deal - I will take the head off this winter anyway!
The term "Tappet adjusters" is olde english & has nothing to do with tappets, it refers to valve clearances. I bet it arose from side valve engines where tappets shoved valves directly
I noticed the same thing Jason did when fitting the mushroom adjusters. The head is not on the bike so I'm not sure what the final geometre will look like but it sure appears the adjuster is going to contact the edge of the valve stem rather than flat on the surface. In other works, you couldn't set the clearance without having the feeler gauge deflected down by the adjuster. All that being said, the mushroom adjusters should work if the geometry could be set up right. I'm using a Megacycle 560HR cam which has .396 lift at the valve. My rough measurement of the length of the exhaust rocker on the valve side is 1 1/8 inches. That means the rocker will rotate through a 20 degree angle during operation. The following pictures show the mushroom adjuster with a line at 10 degrees off square. This represents the edge of contact during a 20 degree rotation if the adjuster is in line with the valve at half lift. The other picture show the mushroom with a line at 18 degrees off square which looks like about the limit of contact on the radius. Also a picture of a beat up standard adjuster. You can see the extent of contact, it's well away from the edge. The length of the contact on the adjuster is determined by the radius of curvature on the end. The larger radius on the mushroom needs a wider area to sweep through a given angle.
Anyway, all this leads me to believe the rocker geometry is hard to get right on the exhaust side particularly with higher lift cams. I'm curious to see what it looks like when assembled. The head's been milled 0.040" but the rods are stock length. Ideally the centerline of the adjuster should be 10 degrees off the valve stem for this cam when it's on the base circle.

Mushroom Head Tappet/Rocker Adjusters (2005)

Mushroom Head Tappet/Rocker Adjusters (2005)

Mushroom Head Tappet/Rocker Adjusters (2005)
There is a third option - ball ended adjusters. They have an articulated ball with a flat that contacts the valve stem.

They always have full valve stem contact over the whole area and produce negligible side loading on the valve stem.

Down side is that I'm not sure there's a drop in replacement for a Commandos
I liked the thought/concept of the mushrooms and therefore, picked up a set from Old Britts. Upon installation, they just didn't look right and ended up pulling rockers to return to stock. Awkward angle, point loading and appeared to need a smaller radius to accomplish their intent. I hate going backwards when I'm trying to move forward. I may try them again in the future after tweaking the heads.

zackybilly1 said:
I hate going backwards when I'm trying to move forward. Z

Welcome to my world. I tell sure is getting old fast with this whole 1 step forward, 2 steps back scenario.
Here we go again. Leo suggested I put mushroom adjusters on my 69 head. $50. I am always reticent to upgrade things like this because it always seems to make more adjustments and spend more money down the line because nothing seems to work out for the better with after market items. (Especially the hooker headers my wife got me for Xmas years ago) Just my experience. I see I can get them from RGM for 7.7 pounds which including shipping would be a whole lot better than $50, but they do not include the lock nuts and as Leo says there are a bunch of them out there with the wrong thread. I'm sure that is the case. I really don't want to have to adjust the length of my push rods.

Any more recent experience with this mod.

Ms Peel has mushroom adjusters that run on hardened caps.
They worked fine and withstood tach needle disappearing
on a stuck throttle event. 7000 hard earned miles so far
but Ken Canaga says head read to run 8K all day.

I lucked out they fit as well as factory clunkers.
Don't remember if Dreer sources or where w/o checking files.
Main benefit is a bit less mass by the Al nuts and hopeful
a bit more wear/friction tolerances.
Valves stems may need milled down to fit the hardened caps
and this it how to get good geometry w/o pushrods fiddle.

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