My Mk1 (1.6) has recently lost a lot of power, now feels very slow to accelerate - had the timing belt changed a few months ago, so wondering if the timing is off - seemed OK after the change, but could it have slipped, or just worn in and now needs re-adjusting?
More worryingly though, it’s a short nosed crank engine, and it looks to me like the crankshaft is wobbling… Have read various horror stories about this, mostly related to timing belt changes…
Have linked to 3 videos - the first while the engine is warming up, the 2nd after a drive, and the 3rd shows the engine revving. Does this look like dreaded crankshaft wobble, or is it just normal engine vibration?
One other thing - the revs have been dropping very low while idling recently (especially while warming up, where it often stalls e.g. when pulling up at the first junction after leaving driveway) - have adjusted the idle speed (took a good few turns anti-clockwise of the idle speed control valve screw!) and that problem now seems better, but just mentioning it in case it could be relevant. It also seems to be running hotter than usual, but not 100% sure on this.
EDIT: revs still drooping, engine still stalling for no reason while warming up, so my ISC valve screw adjustment hasn’t helped after all…
Any advice much appreciated! (video links below - you’ll have to cut and paste them tho, sorry, couldn’t figure out how to embed)
Well I,m no expert either. And it’s not really possible to see much from the video. However my understanding of crank wobble isn’t actually the crank wobbling. It’s the incorrect fitment of the front pulley, usually after a cambelt change, which then makes the key / key way wear and the the front pulley comes loose. This then wobbles. If I,m correct, and it’s more than likely I,m not, I think if you remove the alternator belt and then try to move the bottom pulley by hand it might answer your question.
I,m not sure how this would cause a lack of power though. Hopefully a real expert will comment.
5 yrs ago on my old eunos, the short nose crank pulley “wobbled” the same resulting in a bad loss of power getting worse aver 200 miles coming home. I seem to remember it was the crank keyway/bad tightening/lots of wear. not repairable in my case so I took a flyer & spent £150 on a replacement engine from a scrapped 5, replaced it & turned out it was a better engine than the original not suggesting that as a solution but an option which by luck in my case was brilliant.
some people have welded the pully on, not recommended.
Thanks for replies - I’ve checked the 4 bolts are all tight, which they are, but like someone said, can’t tell much more without dismantling things. I also don’t have the equipment to check the timing itself.
However on friday I’m taking it back to the garage that changed the cambelt a few months ago, so hopefully they can diagnose. They’re mx5 specialists, and have done good work in the past, but if my crankshaft is damaged, it’s hard not to link this the cambelt change, as before this, the engine ran great…
Will report back when have more info!
by the way, the revs are still drooping at idle, and still stalling for no reason while warming up - so it seems my re-adjustment of the ISC valve screw didn’t help after all… Definitely not a healthy engine right now!
Only other clue that may be relevant is that when I checked the airbox/air hoses, I found the connector where the large air hose joins the throttle body was loose. Now this doesn’t just come loose by itself, so I’m having to presume it was left like this since they cambelt change… I’m no expert in this department, but could this have caused dirty/unfiltered air to get into the engine, and could this have caused/contributed to the problem?
I doubt this, we (my mate and I) had the whole air box pipe off to access the drive belts, and I put them back on. The pipe to air box and throttle body is a very tight fit, so takes some pushing to get it seated properly. The clamp is almost redundant, but it’s does stop the connection coming adrift - IMHO.
Good to know, thanks - the more things I can rule out the better - it definitely was fitted on properly, just the clamp that was loose.
I swear it’s lost even more power now, had real trouble climbing hills yesterday, hope it makes it to the workshop tomorrow…
Just wondering, if it is a wobbling crankshaft, is there some point at which the engine just stops running at all, and could this be dangerous if it happens while moving??
If it’s the crank pulley (tight pulley bolts does not mean no wobble) then the power will just get less & less eventually not having enough puff to pull away on a hill.
hope your specialist blokey gets to the bottom of it
I’m afraid this thread isn’t getting the responses I had hoped for - no criticism of existing posters intended.
So I did a search, I suggest Alligatorlizard does the same - just enter ‘Short nose crank problems’ in the subject area of the search, and don’t bother with ‘Posted by’ names at all.
There’s a long post by our original tech expert (John Cookson) Which seems the most detailed of many posts from the past that bears reading, though it raises complex issues which may or may not be necessary.
Also one from Mazda Mender - which is short and to the point. His comment seems - as always short, but to the point that matters - “Never take the pulley off to do a cam belt change” - followed by “If yo do, then always fit a new bolt - never use the old one, and fit a new key as well”
John goes deeper into the key fitting, and while correcting the term ‘Woodruff Key’, which he describes as a ‘Feather key’ which apparently needs ‘crafting for the job’ rather than just fitting a new standard key.
He also describes the exact same symptoms that you are experiencing as potential eventual failure of the engine altogether, where the eventual cure is fit a S/H engine. He also says “Don’t take the car to a Mazda dealer - they will just replace the pulley and fit a new key, which will get you nowhere” He suggests instead, “Take the car to a time served skilled engineer, who has the knowledge to measure clearances, make shims and craft the key to fit.” This assumes the slots in both crank and pulley are still square, and not damaged at all, he can fit a new pulley, but he cant do much with the crank slot. A new bolt is essential, as both point out the earlier bolt will be stretched from previous torquing, and MUST be replaced.
Part of the search reveals several photos, none of which appear to be available, though there is one of a later engine, with an eight slot pulley - why? - I have no idea! There doesn’t seem to be any downloads available on the problem.
As I said to start with, I’m no auto engineer, being of a different field - electrics, but I do know there’s been lots of good - and bad advice in the past, so the search reveals the kind of information I was hoping to see on here. I hope it helps.
Well it turned out to be every bit as bad as I’d feared… the crankshaft was wobbling even worse by the time I got to the specialists so it only took them about 3 seconds to agree with that part of the diagnosis! They then stripped down the front end and removed the main pulley - thing is, there was no damage to the bolts, the key looked fine, so they reckoned the damage had to be internal, e.g. worn crankshaft for whatever reason. So my engine is officially dead… Not much point repairing, and with other expensive repairs imminently needed (rust/sills/roof/brakes/etc) I’ve had to make the depressing decision that it’s probably not worth going thru another engine swap at this stage. This car’s come back from the grave many times over the 7 years I’ve owned it, but sadly, it does seem like the day has come I’m going to have to try to sell it as a project car, and look for something a bit more mechanically/structurally sound.
All those posts about whether or not to avoid SNC engines - probably best to avoid I say!! That said, it was a great engine while it lasted, and extended the life of the car a good few years. But wouldn’t risk a SNC again for any reason.
As for why it failed now, who knows. I did initially connect it to the recent timing belt change (for obvious reasons, if you google “SNC wobble”), but after talking to them in detail about this, I’m satisfied they took all necessary precautions, and like I said, there was no evidence of any ham-fistedness in terms of how the pulley had been replaced.
Anyway, thanks for all the advice! Not much left to ask on this one though I think…
One last thing - despite now barely having the power to move away from stationary, it was still leaving other cars in the rear view on the way home simply due to how supernaturally these things go round corners - so still able to put a smile on your face, even with a drastically failing engine!!
Bad luck for the car to run a crank. If there were movement in the shaft itself I would have expect oil to be pouring out from the crank seal, as well as a horrendous rumbling if the crank/ bearings were that badly worn. In my opinion that car simply wouldn’t run with that much movement in the crank shaft.
The crank pulley on these early SNC cars can be split via the four 10mm bolts, so cambelt can be changed without undoing the main crankshaft bolt AFAIK.
Just looked at the videos - definitely wobble there - revving the engine makes it clear.
Would be interested to see photos of the crank keyway/key and know if the garage removed the main crank pulley when they did the cambelt.
I didn’t photograph the crank key I’m afraid, tho I suppose I could dismantle things again myself if need be. The other day there seemed to be no visible external damage though.
The garage said they did remove the the main crank pulley when doing cambelt - they said it’s impossible to change without removing it?
I have checked this - the short nose crank pulley can be split via the 4 x 10mm bolts to remove the damper and outer pulley. The only reason to remove the inner pulley and crack the crank main bolt would be to replace the crank oil seal if it was badly leaking oil.
Bear with me here, I’m no expert on these aspects of the engine, but I think the part they said had to be removed was actually the outer pulley (which makes sense as you’ve got to remove the timing belt cover at front of engine) - however, is the part you’re referring to (the one that shouldn’t be removed) the bolt at the end of the crankshaft that is revealed when the pulley is removed? The part that the key fits around? Actually there’s pic in the thread you linked to: http://i457.photobucket.com/albums/qq299/mark_wendon/MX5%20Westfield%20Build/Engine%20Rebuild/IMG_2733.jpg
They were certainly turning this main bolt (with difficulty) when I took it in to get them to assess what was wrong. And you would think, when I mentioned to them that I’d heard you shouldn’t remove the pulley, they could have set me straight and explained that it was probably the main crank bolt that I’d been advised not to remove - and then let me know whether they’d done this or not… They instead assured me they used a system of clamps, I forget the details, but apparently some sort of specialist equipment to ensure nothing moved out of place while changing cambelt.
Hmmm… It is very worrying that the work they did could have caused this engine damage, though I don’t know how I’d go about proving this one way or another at this stage. If I was sure it was due to their work, I’d certainly not be letting this go so easily…
Can anyone suggest what to look for, or what to ask, to figure out if they did do something inadvisable? Or any other info/links/threads that may help me to understand the SNC issues as relate to timing belt changes?
I’m basically now shopping for another mx5, and while I’m looking forward to finding a somewhat newer and more reliable car overall, the fact is, that if my current engine hadn’t failed, there’s no reason why my old '5 shouldn’t have stayed on the road for a good while yet. If it’s just bad luck, and wear-over-time on what is acknowledged to be a less bullet-proof version of the 1.6 engine, then that’s one thing - but if something was done to cause this damage that could have been avoided… not good!!
