M8 Adjustable Rocker Arms

Hey, welcome to Fix My Hog, I'm Mike Roen. In this video, we're gonna kinda give you something that nobody really ever thinks about. You know the M8, typically still a brand new motor. Not too many people diving into them but as you can see, this motor's coming apart and he hurt it really bad. And so, I just wanted to show you something that really is not on anybody's radar yet because this whole new configuration's all new design to the Harley world. I mean it's been in metric bikes for many years but what Harley has is they've got a four valve head. They've got one rocker arm here controlling to depress both valves at the same time. Everything's all wonderful when it's all new but let's just say down the road, 50,000 miles, things start to wear. If your valve face wears, the valve seat wears. The tip of the rocker arm can start to wear. And of course the tip of the valve. Pretty normal on a regular Evo or Twin Cam. Life would be okay because the lifter would just compensate for that. It'd take that clearance up. Well, if you think about this, and you look at the design of this, you're depressing two valves at once. So, let's just say, and I'll show you here, let's go to the head I've got on the table and I'll kinda help explain why we're looking at valve tip heights so crucially on a M8. So on this core head, what we do is, we just put an intake valve in here. And I got a little gauge to measure the tip height. So anytime we do a valve job, what we're doing is we're recording the tip height of the valve. Now, we're gonna take that same valve, we'll stick it in the other hole here and do a comparison. And believe it or not, right from the factory, the tip height is exactly the same 'cause Harley knows it's very crucial that those tip heights have to be the same for this rocker arm to work the same. Now imagine you send your heads out to the coolant guy, cylinder head guy. He does a valve job. He's not thinking about your rocker arm. He's thinking old school, one valve, one rocker arm. Doesn't matter if the tip heights change 10, 15007 inch. But it does. Can you imagine the difference in these tip heights? You've got a 10,000th difference. The lifter's gonna adjust to one valve only. Now you've got this difference of 10,000ths. What are you gonna do? Well, Harley actually came up with a Screamin' Eagle adjustable rocker arm and you won't even find it in their Screamin' Eagle book yet. I don't know why but they do make it, cause I've got one. So, here's your deal here. And basically, I mean metric motorcycles have been doing this forever and ever on their four valve design. They typically have a rocker arm adjustment on both valves. This just makes it simple. And all we're doing really is we're gonna take this rocker arm. And you can see it's just threaded here. And you run it down to zero clearance. You just lightly touch it off here and once that's zeroed out, you got no up and down movement. Take it and they want you to torque this thing. They've got a speck in there, it's like 120 inch pounds. Boom, there you go. So now, you've got a proper tip height. I mean, if you weren't able to do that, you're gonna have a valve that's not contacting the seat all the way, dissipating that heat, burning the valve. So Harley realized it's very important. But for you to think about it down the road, I mean, right now, your bike's low mileage, you probably haven't cracked the seal or you're not taking it apart but in time, when you get time on it and you don't wanna take the motor apart, this isn't a bad option. Or if you're doing a 114 kit on your bike, now would be the time to do it. The labor would be virtually free, so. Anyway, at least you got a nice little exposed view of an M8 here, if you've never had your motor apart or actually got to see one. You can, you know, see the different configuration over the Twin Cam. It's similar but it's different. Anyway, that gives you a nice birds eye view of the whole rocker arm setup on that thing. Really, you know, at the end of the day, it always comes back to the motors and air pump. It's gotta be efficient. That's gonna make it efficient. If you were to do a leak down on new engines or used engines, the leak down on every bike is gonna be different just because of the valve train typically. I mean, you know, if the valves being held open just a little bit, you don't have an efficient air pump. You don't have an efficient motor, so. Something to keep in mind. Thanks for tuning in again and always check out Fix My Hog for more informative videos.