Rocker Arm Modifications

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The old hydraulic rocker arm issue. Personally I believe Mazda did not engineer their valvetrain in these trucks to be halfway bullet proof with a hydraulic valvetrain. Because of this I see strong gains in converting to the mechanical rocker arms (Sold Here) used in the 87-88 Mazda B2000 and 626. For the most part this modification is a direct bolt on but for those going farther you can make some improvements to reduce weight and chances of breakage. If you buy them from you will want 4 RAMA8A and 4 of RAMA8B rocker arms. Since the valvetrain has a known inability to maintain control of the valves at high rpm or higher than stock acceleration, and many issues with oil starvation I would consider any modification to reduce weight or increase lubrication to be far more important to relieving stress risers, especially if a performance cam grind is being used.

Shown below is a used rocker arm for illustration.

As you can see, especially with the picture on the right the stock castings are not the cleanest. All of these casting imperfections are a potential problem and are stress risers.

Think about it, if you take a piece of wire and put a tiny nick in the insulation and start bending it back and forth, where is the wire going to break? Where the nick is right. Or if you have a piece of metal protruding out of something smooth and it rubs against another object its going to get broken off, usually taking material below with it. This is what these stress risers are doing to the parts, especially on cast aluminum. To fix this we are going to do the same thing as Beam Polishing on connecting rods. This also helps lighten the part which by the time you are finished installing the mechanical rocker arms and cut you're modifications you will have lightened up the valvetrain by the weight of 1 full hydraulic rocker arm which is about 80 grams. We will also reshape part of the rocker arm and do some minor drilling to increase oil flow to the cam lobes.

Beam polishing is removing casting flash and burs off the surface of the part which can cause potential failure under high stress. Since we are actually removing metal to make the part stronger it is very critical that you know how and where to remove it otherwise you will weaken the part.

To do this you will probably need a dremel tool, a carbide bur like in the pictures below or sanding drum, 300 grit and 600 grit sand paper. You want to take the carbide bur or sanding drum and remove all of the burs and stuff sticking up from the surface, only take off the minimum amount of metal to bring it level with the surface.


When taking metal off you have to be careful which direction the tool is turning in relation to the part. You want all of the scratches to be going the same direction as the long axis of the rocker arm. This would mean that if you are using a carbide bur you want to try to keep it like I have shown in the picture above. If you are using a sanding drum you will want to try to keep the drum at a 90 deg angle to the long axis of the rocker arm, otherwise the scratches will make it more prone to break (like that notch in the wire).


Now that you have gotten all of the casting slag and burrs off it is time to slightly round most of the sharp corners. Also any abnormal indentations in the rocker arm need to be very carefully blended. Sharp corners are also stress risers. Think of when you strip a bolt or nut, the points are the first part to go. You don't need to round them much, maybe about 1/16“ depending on where you're rounding it.


Now we will get a little more involved. We are going to remove that great big round spot from where they poured the metal into the mold. This spot will probably be the largest effect on the strengthening of the rocker arm. It is big and bulky adding to weight of the rocker arm and it is on the lash adjuster side of the rocker arm meaning it has more reciprocating. Just think at around 4,000 rpm each of these rocker arms will be moving up and down at about 33 times a second.


Next we are going to cut the oil groove. This is going to be right above the cam follower. The best tool to use for this is probably the carbide burr shown above as it will give the parabolic smooth shape you want.


On the stock rocker arm oil puddles in the pocket where this groove is, the result is as the rocker arm is moving it slings oil up towards the valve cover. Oil all over the inside of the valve cover doesn't really help out lubrication much and the oil slung all over the place causes windage. This groove allows the oil to flow down the rocker arm and onto the cam lobe which might help decrease cam and cam follower wear not to mention reduce windage and rocker arm weight. Note that we are NOT removing material here to reduce weight, lighter weight just comes with the modification, the main purpose of the oil groove is to hopefully get more oil to the cam lobes. On the intake rocker arms you will want to aim the groove more towards the rocker shaft and on the exhaust aim the groove away from the shaft, the idea is to get the oil to drain onto the cam lobe before it reaches contact with the cam follower. Do not cut into the ridge of the rocker arm. I have modified a few setups like this an never had a problem with the rocker arms, even after pounding them pretty hard.

Finally take your 300 and 600 grit sandpaper and polish the aluminum casting, you will want to move the sand paper along the long axis from the cam follower end to the lash adjuster end. You don't want the rocker arm to be perfectly polished. Engine parts need surface area to dissipate heat to coolant, oil, and air, polishing the rocker arms perfectly smooth will reduce this surface area removing some ability to remove heat. Basically all you want to do with the sandpaper is even out the overall surface of the rocker arm to distribute stresses more evenly.

The most important modifications will come with increasing lubrication to the came lobes and valve tips. During normal operation a lot of pressure is placed on the cam lobe during peak lift. This causes much of the oil film on the cam lobe to be sheared off and metal to metal contact is made. Because of the oiling arrangement for the cam a quick and dirty solution is not easy. Besides the oil tray made into the head under the camshaft the only other lubrication for the cam lobes comes from a tiny hole in the rocker arm. This works great on the intake side because oil is sprayed onto the cam lobe right before the cam follower makes contact. On the exhaust side however the oil spray makes contact after the cam follower makes contact. This means that most of the lubrication on the exhaust lobes comes from the oil tray under the cam. If you are witnessing cam wear, or gouging of the cam lobes on the intake side we recommend slightly enlarging the oil jet drilled into the intake rocker arm. You want to use the smallest drill bit possible that will still enlarge the hole, .002-.005” can go a really long way and we don't want to reduce oil pressure to the rest of the valve train. Before drilling use a stiff pin of some sort to view the angle of the hole and try to match it when drilling, this angle allows the oil to be squirted right before the follower makes contact on the cam, if the angle changes you can significantly reduce the amount of oil on the cam lobe instead of increase it. Currently we do not have any recommendations for helping lubrication on the exhaust side since the oil jets in the exhaust rocker arms are pretty much useless, drilling them larger will not help the problem.

Modifications performed on this page are at your own risk although the author of this page has performed these modifications with some success they can cause severe engine damage if performed incorrectly. If you have any doubts about your ability to perform these modifications do not perform them, (or is not liable for any damages that may incur.

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draft/rockerarm.txt · Last modified: 12/09/2020 04:01 by reyxil
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