Slippery
Slippery UltimaDork
12/22/24 3:04 p.m.

TLDR: 1990 (09/89) Miata on original timing belt. What are the chances of having keyway problems when doing a timing belt? 

My middle son just got his learner’s permit. We were talking cars and he wants a Miata “the one with the pop-up headlights”. Well, I happen to have an NA stored that I barely use, so I am thinking of getting it ready for him. 

I bought this Miata many years ago from a neighbor, it’s a short nose 1.6. I tracked it twice and never changed the timing belt, which probably has the 150k miles the odometer indicates and 35 years. I never cared because if it popped, iirc it’s a non-interference and I could just tow it home. But I'd like to do the timing belt if I pass it on. 

What are the chances the keyway will be a problem? Is this an overblown problem or are the chances high? If it is opened up, look for a replacement engine or do the fix?

EvanB
EvanB MegaDork
12/22/24 4:08 p.m.

It's been many years since I've thought about them but I think most of the issues stem from issues when replacing the belt. If it doesn't currently have issues you should be fine replacing the belt and installing the crank bolt with loctite and the correct torque.

Keith Tanner
Keith Tanner MegaDork
12/22/24 6:18 p.m.

Yup, Loctite, the correct torque and assembly and put it out of your mind. They did sometimes fail, but they failed fastest when the bolt backed off. Even the long nose cars don't like that. 

If the keyway does take damage, the Loctite fix (an actual recipe, not just using blue threadlocker) works. 

Remember that if the belt breaks it may not damage the engine, but sure will ruin your day. I saw one belt break at a big Miata event in Moab with the owner hundreds of miles from home. Sure didn't make for a fun event. Do it now,  do it right and you won't risk having to depend on a Jeep mechanic who's never seen a Miata before :)

I assume the front main seal is vomiting all over the front of the engine by now. Your water pump needs to be changed too. 

Slippery
Slippery UltimaDork
12/23/24 11:36 a.m.

OK, thank you guys.

So, I guess the keyway opening happens after the first timing belt if the bolt is not properly torqued and locked?

Anyways, yes, all front seals and water pump are on the list. The rest of the car is in very good mechanical shape ... I was just afraid of opening a can of worms so I left everything behind the tbelt alone.

I will also need to source a factory cat-back exhaust and figure out the AC leak, otherwise its a solid car (although ratty looking) for a 16 year old.

Apexcarver
Apexcarver MegaDork
12/23/24 11:49 a.m.

"Ratty"   uhhh, no?  That looks pretty good!

Keith Tanner
Keith Tanner MegaDork
12/23/24 12:42 p.m.

The keyway opening is wear that happens if the pulley is allowed to move around. It's only there for alignment, and once it's asked to be load bearing things go downhill. So yeah, loose bolt. 

I have a few extra AC parts (hoses, etc) if you need them. 

WonkoTheSane
WonkoTheSane UltraDork
12/23/24 12:53 p.m.
Apexcarver said:

"Ratty"   uhhh, no?  That looks pretty good!

Yeah, Slippery's definition of Ratty and mine are a wee bit different :)

Either way, Keith nailed all the important bits as always, but this sounds like a great first car project for your son!   I'm looking forward to doing maintenanc-y kinda things with my kids on their cars instead of mine in a few years. 

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