The Miata is finally back together, and Jeebus H. Christ I'm wore out. That's the most total hours of wrenching in a 3 week period I've ever done.
I did the T-belt/tensioner/idler/water pump/cam-crank seals/CAS O-ring/valve cover deal. I've done many T-belts over the decades, and work carefully, following the factory manual for timing and accessory belt tension specs, everything was thoroughly cleaned, checked twice. Crank nose was perfect but I reassembled w/ new key, bolt, thorough clean, Loctite...All OCD style.
Back together there is a distinct whirring noise coming from the from of the engine. It sounds as though it's coming from the under-front-of-valve-cover region. I see at miata.net there's precedent for this happening.
Common thing, wears in goes away? open it up and have a look? drive it a few miles and see?
Over tight belt is probably the most common problem. Others might include the teeth slightly worn on the gears, so the new belt is not entering each tooth cleanly, or there is a small mis-alignment of the tensioner, causing the belt to run out or in on the pulleys, rubbing on the pulley edge. I'd probably pull the cover if its easy, and run the engine to see if there is anything obvious there. It might shut up after a couple hundred miles, too- wear the fuzzy bits off the belt or something.
It's pretty tough to over-tighten a Miata timing belt. Unless you guys are referring to an accessory belt.
What is common is having the timing belt covers refuse to clip together behind the water pump pulley. The plastic cover then leans up against the pulley and makes as noise as it erodes away.
I have put t-belts on a few different Mazda B-series four cylinders (always in FWD applications though) and the whirring sound comes from an overtightened belt.
The cars I've done have the following procedure (in a nutshell):
Push the tensioner all the way loose and tighten the bolt to hold it there
Put the belt on at TDC
Rotate the crank 3 teeth
Loosen the bolt that holds the tensioner
Let the spring in the tensioner do its thing
Tighten the bolt to hold the tensioner in place
Done!
A couple of times I tried putting a little extra pressure on the tensioner to make sure the belt was TIGHT and both times it sounded bad. I relieved the tension and did it the way the book said to and the noise disappeared instantly.
I'll pull the accessory belts and see what it sounds like - they'll need to come off for what's next...
BTW, I tensioned it per the factory manual - 2 turns through to verify correct installation then 1-5/6 turn to tensioner mark, loosen tensioner bolt, tighten tensioner bolt.
Place straightedge atop belt over cam pulleys, apply 10kg to midpoint of belt, measure deflection. 9.5-11mm acceptable range (or thereabouts - book is at home)
I had a bit more than the big end of the acceptable measurement - I went back to the tensioner mark and nudged the pulley over a tiny touch. The deflection at 10kg was 10mm.
The sound is more continuous than belt teeth should sound - considering it a day later. I'm guessing it's a belt shroud. We'll see anyway tonite.
I've gotta get the M3 ready for NJMP this weekend and the Mee-otter has to be driveable to the alignment shop the following Tuesday AM...
motomoron wrote:
BTW, I tensioned it per the factory manual - 2 turns through to verify correct installation then 1-5/6 turn to tensioner mark, loosen tensioner bolt, tighten tensioner bolt.
Perfect. If you just follow the rules, it works well. If it's not a shroud, I'd go back and undo the "little bit extra" you gave it. You can do this by just removing the upper part of the shroud above the thermostat neck and reaching down to the tensioner mark with a wrench. There are indicators on the lowest part of the shroud to let you do this easily - using the ignition timing mark at the marker at 12 o'clock. Quick and easy with a minimum of disassembly.
