Timing belt and short nose crank.
Discussion
Next weekend I will be doing a big service on my car. It's just ticked over to 155,000km and as I don't know when anything was last done on it I'm going to give it the works for peace of mind.
My car has a short nose crank and I've read all the stories of engines being destroyed because of the issues some can have. My workshop manual says take the crank bolt out, other guides I're read say you can leave it on and still change the belt. I'm in two minds with what to do.
The crank oil seal isn't leaking as far as I can tell so I don't know if I should bother changing it. Part of me says that there isnt anything wrong with it, so don't f
k with it but the other part of me thinks that it must have had at least one belt by now so the bolt has probably been out before and it's still ok.
I want to know what other people's experiences/ thoughts on this are so I can finally make my mind up.
As a side note, next moth I'll be driving to Newquay from my house and it'll be my car's first big trip anywhere, around 350 miles each way so aside from giving the engine a proper going over what else would people recommend I check out for any potential problems?
My car has a short nose crank and I've read all the stories of engines being destroyed because of the issues some can have. My workshop manual says take the crank bolt out, other guides I're read say you can leave it on and still change the belt. I'm in two minds with what to do.
The crank oil seal isn't leaking as far as I can tell so I don't know if I should bother changing it. Part of me says that there isnt anything wrong with it, so don't f
k with it but the other part of me thinks that it must have had at least one belt by now so the bolt has probably been out before and it's still ok.I want to know what other people's experiences/ thoughts on this are so I can finally make my mind up.
As a side note, next moth I'll be driving to Newquay from my house and it'll be my car's first big trip anywhere, around 350 miles each way so aside from giving the engine a proper going over what else would people recommend I check out for any potential problems?
Edited by MikeOxlong on Sunday 30th March 17:31
Some good info here, might help to decide what to do with it:
http://www.miata.net/garage/crankshaft.html
Overall it seems to suggest a new bolt and some loctite:
"Yes, most of the fault lies with the weak design that asks too much of that bolt. For this reason, the solution is NOT to leave the bolt untouched. That bolt is becoming older and older everyday. Every time you start the engine, the risk for failure increases. The bolt should be on a regular replacement schedule. I would recommend annually.
If everything is in order, clean up the crankshaft and bolt shoulder seating surface with brake cleaning spray. Toothbrush the inside of the crankshaft threaded hole. Apply Loctite thread locker or sleeve retainer to a new bolt. Install NEW bolt and key. Torque to 87 foot pounds."
http://www.miata.net/garage/crankshaft.html
Overall it seems to suggest a new bolt and some loctite:
"Yes, most of the fault lies with the weak design that asks too much of that bolt. For this reason, the solution is NOT to leave the bolt untouched. That bolt is becoming older and older everyday. Every time you start the engine, the risk for failure increases. The bolt should be on a regular replacement schedule. I would recommend annually.
If everything is in order, clean up the crankshaft and bolt shoulder seating surface with brake cleaning spray. Toothbrush the inside of the crankshaft threaded hole. Apply Loctite thread locker or sleeve retainer to a new bolt. Install NEW bolt and key. Torque to 87 foot pounds."
That article is one of the reasons why I can't make my mind up.
It reckons that 92 onwards cars are fine from the issue, however my car is a 92 and when I was checking it the crank pulley indicated it was the short nose version as it had 4 holes in it. I'll check the vin numbers tomorrow I think.
I think I will end up changing it and putting a new bolt in like you suggest. If the worst should happen I can get another engine from EBay for 170 quid.
It reckons that 92 onwards cars are fine from the issue, however my car is a 92 and when I was checking it the crank pulley indicated it was the short nose version as it had 4 holes in it. I'll check the vin numbers tomorrow I think.
I think I will end up changing it and putting a new bolt in like you suggest. If the worst should happen I can get another engine from EBay for 170 quid.
The issue is confined to the short nose crank. If your engine has the short nose crank, replace the bolt and key (and torque it to about 85 pounds). If your engine doesn't have the short nose crank I wouldn't worry about it too much. The big issue is that people don't replace either and torque it to 120 pounds (the proper torque for the new crank).
If you have a 92 or newer you should have the new crank. To know for sure which one you have without taking everything apart, the pulleys are different. The old pulley has 4 holes on the front face of it (exposing the rubber on the inside of the pulley).
If you have a 92 or newer you should have the new crank. To know for sure which one you have without taking everything apart, the pulleys are different. The old pulley has 4 holes on the front face of it (exposing the rubber on the inside of the pulley).
An update for anybody who's interested.
I took it all to bits and changed the belt. I left the bolt as it was as it seemed OK underneath. The pulley was knackered so I ordered a new one and popped it on with some new bolts and thought that was that but it started to develop a wobble. Today I stripped it all down again and inspected it for anything that was causing it and it was clear that the bolt was not OK.
Removed the bolt (which was loose) and the crank gear to see the condition of the crank nose. For a car that's got 150K on it it wasn't too bad, there was a tiny bit of wear on the keyway (1mm) but nothing outrageous.
As a preventative measure I cleaned the whole lot up with degreaser, did the loctite fix and put a new bolt, gear and key in with some 243 on the bolt torqued up to 85/87 lb.ft. I'm waiting now for the fix to set before I put it back together properly and start it up. I also changed the oil seal as it was a bit tatty.
One question I'm unsure of though is that whilst I was changing the oil seal and cleaning it all I managed to move the crank off it's mark. I couldn't turn it back to the mark so I used the old bolt to turn it clockwise back round to the mark (1 turn) I made sure piston 1 was back at TDC. Is the engine still in time or do I need to turn the crank through some more turns to set it back how it was before I put the belt back on? Google hasn't helped.
I took it all to bits and changed the belt. I left the bolt as it was as it seemed OK underneath. The pulley was knackered so I ordered a new one and popped it on with some new bolts and thought that was that but it started to develop a wobble. Today I stripped it all down again and inspected it for anything that was causing it and it was clear that the bolt was not OK.
Removed the bolt (which was loose) and the crank gear to see the condition of the crank nose. For a car that's got 150K on it it wasn't too bad, there was a tiny bit of wear on the keyway (1mm) but nothing outrageous.
As a preventative measure I cleaned the whole lot up with degreaser, did the loctite fix and put a new bolt, gear and key in with some 243 on the bolt torqued up to 85/87 lb.ft. I'm waiting now for the fix to set before I put it back together properly and start it up. I also changed the oil seal as it was a bit tatty.
One question I'm unsure of though is that whilst I was changing the oil seal and cleaning it all I managed to move the crank off it's mark. I couldn't turn it back to the mark so I used the old bolt to turn it clockwise back round to the mark (1 turn) I made sure piston 1 was back at TDC. Is the engine still in time or do I need to turn the crank through some more turns to set it back how it was before I put the belt back on? Google hasn't helped.
I don't recall ever having problems with the crank needing to be rotated more than once - thinking it through, the pistons will end up in the exact same positions after every revolution of the crank, so just get the timing mark on the crank pulley in the right place:
http://www.miata.net/garage/timingmarks_closeup.jp...
then line up the E and I on the camshaft pulleys as per the metal plate behind them:
http://www.sergionicolau.com/viatura%20-%20mazda%2...
I found I had to use a ratchet to hold one camshaft slightly against the valve spring force to get it perfect (can't remember which one it was) otherwise it ended up 1 tooth out.
http://www.miata.net/garage/timingmarks_closeup.jp...
then line up the E and I on the camshaft pulleys as per the metal plate behind them:
http://www.sergionicolau.com/viatura%20-%20mazda%2...
I found I had to use a ratchet to hold one camshaft slightly against the valve spring force to get it perfect (can't remember which one it was) otherwise it ended up 1 tooth out.
That's what I thought, but then I started overthinking the matter and doubted my own logic. I've got a cam locking tool to help hold things down as last time I did this holding the intake cam against the valve spring whilst trying to slide the belt on without missing a tooth was a pain in the arse.
I put it all back together today and although it's better than it was, I'm still not really happy with it 
It looks to me as if there is still a bit of a shimmy/ wobble going on. The new pulley I put on had two sections drilled out of the back, I presume to balance it so I don't know if its the pulley that's ever so slightly out or if it still has a problem.
I got a video on my phone of it doing it's thing, I'd appreciate it if someone with more experience than me could watch it and see what they think.
http://www.youtube.com/watch?v=xy0qoXK7Cls
It looks to me as if there is still a bit of a shimmy/ wobble going on. The new pulley I put on had two sections drilled out of the back, I presume to balance it so I don't know if its the pulley that's ever so slightly out or if it still has a problem.
I got a video on my phone of it doing it's thing, I'd appreciate it if someone with more experience than me could watch it and see what they think.
http://www.youtube.com/watch?v=xy0qoXK7Cls
Mine did it way worse than that for all the years I had the car and nothing bad ever came from it. I was really concerned at the start so I swapped to another pulley, but that one did the exact same thing, so in the end I just ignored it. No idea if my current 1.8 does it, but given how cheap and available replacement engines are I don't really worry any more until something either makes a nasty noise / smell , or falls off.
I guessed that it may have been the rubber joining bit in the pulley was a bit worn causing the wobble, but not sure if that's right or not.
I guessed that it may have been the rubber joining bit in the pulley was a bit worn causing the wobble, but not sure if that's right or not.
That's reassuring. My usual mantra is "fk it, that looks alright from my house" but the car is at my house so I can't hide from it.
As long as it's not going to suddenly fail and leave me waiting for the breakdown van to arrive then I'll just live with it.
If it does break then I have an excuse to buy more garage toys to fit a new engine.
Thanks for your advice
k it, that looks alright from my house" but the car is at my house so I can't hide from it. As long as it's not going to suddenly fail and leave me waiting for the breakdown van to arrive then I'll just live with it.
If it does break then I have an excuse to buy more garage toys to fit a new engine.
Thanks for your advice
Try hitting it with something like a hide mallet (or a metal one using a wood drift to dampen it) a bit to see if it moves at all. Don't overdo it as if it's loose enough to wobble when spinning then it wouldn't need much to move with a tap.
I suspect it's just the pulley itself that's a bit out. Certainly on mine you can see some wobble if you look at the face of the pulley but when you look at the belt itself it's rock-solid so it's just machining tolerances on the outside where it doesn't matter.
I suspect it's just the pulley itself that's a bit out. Certainly on mine you can see some wobble if you look at the face of the pulley but when you look at the belt itself it's rock-solid so it's just machining tolerances on the outside where it doesn't matter.
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