mx5cartalk.com

While doing the radiator change this weekend, I noticed the pulley on the end of the crankshaft seems to move forwards and backwards a bit when the engine is running.

From reading on miata net, this is potentially a symptom of imminent crankshaft failure, which concerns me

How far does it normally move?

I'll try any grab a video of it moving...

A low quality movie of the crankshaft...

movie...

That sux Liam,

Take it to your mechanic and get the crank pulley taken off and check if the keyway is damaged.

Who did your timing belt change?

Does it affect NB8B's too?

My last one (NA6) wobbled way worse than that, and it still went strong.
The rods however look like Uncle Arthurs

Okibi wrote:That sux Liam,

Take it to your mechanic and get the crank pulley taken off and check if the keyway is damaged.

Who did your timing belt change?

Timing belt was done at a dealer at the 100k service.

It's 3k off the 200k service...

Is the bolt tight Liam? If so I would think that it has been that way since the belts were replaced last - your opportunity to correct it will come with the next replacement. New pulley and key should do the trick. It is amazing how much punishment a crank can take - I've seen a pulley run out over half an inch and did no damage

Yeah If it's been like that for 97 thousand k's it's not going anywhere

I looked at it with one of the mechanical gurus here at work, and it seems like the pulley is not straight, but the bolt is centred ok, so it just looks like the pulley is dodgy

The PWR radiator looks damned sexy though I'll take some pics soon...

I updated my sig, as the car is not quite bone stock anymore

Thanks for the ideas and advice guys

BJ sent me his suggested solution

OI You forgot the ARp head bolts, end caps, the T28 aswell just to add some spice to the rear wheels

BJ

PS I think a new pulley and key may do the trick aswell.

bjones wrote:OI You forgot the ARp head bolts, end caps, the T28 aswell just to add some spice to the rear wheels

Of course we'll be using your new shed and hoist (when it's in) to do all this

Wow, that certainly looks nasty!

It goes in for the 200k service soon, I'll get i sorted out then...

Well Jason from ttauto has had everything apart to measure it all, and while there is a bit of end play and runout it's nothing spectacular. He's replacing the pulley and all should be good!

He did say that a lot of the stuff that was meant to be done at the 100000km service looked like it had never been touched.

So my car should be ready shortly, with a new less wobbly pulley, fixed oil seals and fixed coolant leaks (the new gates hoses don't appear to be very good, or it could just be my installation work )

Hurrah!

i had the exact same problem recently at the mx5 challenge day at wakefield.

my key ended up shearing and i had to vulture a replacement of a guys SE that had broken no4 piston. though in the process of testing my spark leads and plugs i stuffed one or more of my plug leads so the car still wasnt happy.. running on a questionable amount of cyclinders.. still went out for the last race on the sunday though and didnt come last

the design from factory is pretty terrible with the pulley wheel only engaging the crank shaft by a little over 5mm the rest of the cranks nose as its been refered too is taken up by the timming belt gear. apparently its becoming a common problem with the nb8a's as the approach the 10year mark.. the keyway and key just wear out getting sloppy and eventually something gives in. that being said if the keyway is worn a new key and pulley will not fix it for ever, the keyway will need to be repaired.. which means new crank shaft other wise it will just keep chewing up keys untill its more flogged out than borats sister.

im hoping the replacement key and pulley in mine lasts atleast a year as i rebuild another motor.

and I thought this was only an issue with the early NA6's

My car has 200000km on it and recent observations lead me to believe the 100000km service wasn't done all together well, so I wouldn't take this result as an indication that there is anything inherently wrong with the NB8B engine.