Clattering at specific load and rpm in valvetrain

kz6fittycent

I have an odd situation that is irritating me.

I have adjusted my valves and they are quiet at idle and through the rpm range, with an exception. A weird one.

When I am cruising at around 2k rpm (speed doesn't matter really), there is a loud clatter that sounds like the valves are not adjusted. The sound/clatter is load dependent. Meaning, if I am just cruising with almost no load on the engine, the noise is loud. If I even touch the throttle slightly to accelerate, it's quiet again. If I'm going about 70mph and the rpms are around 3000, it's quiet and smooth. If I decelerate, the clatter goes away. It's weird!

I can get it to happen with the truck in neutral and I operate the throttle and keep moving it back and forth. It's like there's some lash there when it's hot - and my next step is to do a hot valve adjustment; since I did it with a cold engine.

I am also about to change the timing belt, etc since it's due, but the sound isn't coming from there, it's definitely in the valve train.

Just wondering if this is normal for the B2000? I have read many threads where people have adjusted their valves until their fingers bleed and these engines just make a lot of clatter.

Anyway, I love my Mazda, and thanks for this forum @MazdaMitch !! This is perfect.

MazdaMitch

kz6fittycent I once had a similar rattle and it was back when I had cat converters on it and there was a "cage" around one? I don't know what to call it but it had a piece of gravel trapped in it and it was rattling at certain RPM ranges

kz6fittycent

That's a strong possibility. I replaced the entire exhaust on my truck with headers and welded up an exhaust all the way back. It could be a rattle I'm not seeing and could be resonating up thru the headers and into the head - making me think it's something it's not.

I need to get it up on ramps and start looking more closely.

Thanks man!

kz6fittycent

Definitely exhaust! It's basically two things on mine.

One of the header primary tubes is just a little too close to the lower control arm where the torsion bar mounts up.
The exhaust clamps I got were tight when cold and loose when hot! So I replaced them with different ones and it's significantly quieter.

I still need to clearance that one primary (I need a punch to get in there) and I should be good to go! Thanks @MazdaMitch !

brapamaldi

i have the same issue. rattling at a certain rpm range. definitely sounds like its coming from under the car and not in the engine bay. was supposed to get it up on ramps this weekend to investigate but had to put new brakes on my wifes car instead so didnt get to have a look yet.