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Can My Crank Be Saved?


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#1 BaronVonchesto

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Posted 09 August 2019 - 06:10 PM

Started my engine this morning to an awful squealing sound coming from the flywheel side of the engine. Took off the clutch cover to find the flywheel bolt had somehow come loose. Was able to remove the flywheel without a puller. Just pried it off with screwdrivers. Thats how loose it was!  O_O  To think the car seemed to be driving fine just yesterday...

 

For those who havent been following my posts, I just rebuilt my engine myself, and this engine is now 3 or 4 weeks old, and has done just under 400km so far. Don't know how a torqued up, threadlocked and lock-tabbed flywheel bolt can come loose. My mechanic suspects the flywheel key wasn't on the right way. The fact that I didn't know they only went in one way lends credence to this guess...

 

Anyway, took off the flywheel and was horrified to find that my crank taper had been scored. It's grooved quite deep in some places. The question is can it be saved? Perhaps by having it ground and sleeved? What can I do?

 

It's a nice 12A298 crank which i just got balanced for my rebuild. I'll cry if I have to scrap it...

Attached File  IMG_20190809_230836.jpg   31.61K   6 downloads



#2 wile e coyote

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Posted 09 August 2019 - 06:21 PM

Sorry that's scrap....



#3 Moke Spider

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Posted 09 August 2019 - 06:50 PM

It's bark is worse than it's bite I think.

 

Clean it up and then let's see. You would be best off to remove the crank from the engine to do this and it would be preferable to do it in a lathe.

 

No doubt the flywheel will be damaged, but finding another of these shouldn't be too hard.



#4 imack

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Posted 09 August 2019 - 07:52 PM

I'd be surprised if that was salvageable.

#5 BaronVonchesto

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Posted 09 August 2019 - 08:29 PM

It's bark is worse than it's bite I think.

 

Clean it up and then let's see. You would be best off to remove the crank from the engine to do this and it would be preferable to do it in a lathe.

 

No doubt the flywheel will be damaged, but finding another of these shouldn't be too hard.

Actually the flywheel doesnt appear to be damaged in any way. Only the flywheel boss which doesnt cost that much to replace.

 

However im not too keen on spending money sending the crank off to be machined only as a trial. it'd probably cost a similar amount to get a replacement crank (though it would have to be balanced again)

 

how important is the clearance between the flywheel and the crank in this case?



#6 BaronVonchesto

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Posted 09 August 2019 - 08:43 PM

Here's another picture of the Crank. The triangular chip at the front was there from before, perhaps the last person to rebuild the engine damaged the crank a little, since this crank isn't the original for this engine (its an A+ 998 not a cooper)

 

Attached File  IMG_20190809_230219.jpg   52.56K   2 downloads

 

Also the flywheel boss

Attached File  IMG_20190809_230855.jpg   55.13K   1 downloads



#7 phillrulz

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Posted 09 August 2019 - 08:56 PM

Sounds stupid, why does everyone say cranks like that are scrap, back at my old work the machine shop would spray metal deposit shafts to re build diameter then turn back down. 



#8 cal844

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Posted 09 August 2019 - 09:50 PM

That could be saved by welding and then refacing or even using molten metal and refacing, both not easy but would save the hassle

#9 Magneto

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Posted 09 August 2019 - 10:08 PM

But in both cases the crank would have to be removed from the engine.....if it was me I'd look for another crankshaft. And a new flywheel...

 

I would also be wondering what else you might have done wrong or missed given that you didn't notice that the keyed washer only goes on one way.......a book would be a good idea.


Edited by Magneto, 09 August 2019 - 10:10 PM.


#10 Moke Spider

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Posted 10 August 2019 - 01:00 AM

On on engine like this, there only needs to be 50% contact area on the Taper between the Crank and the Flywheel.

 

Looking at the Crank as is, I'd say cleaned up, you'd have close to 70%, but clean it up first.



#11 BaronVonchesto

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Posted 10 August 2019 - 01:42 AM

But in both cases the crank would have to be removed from the engine.....if it was me I'd look for another crankshaft. And a new flywheel...

 

I would also be wondering what else you might have done wrong or missed given that you didn't notice that the keyed washer only goes on one way.......a book would be a good idea.

i have a haynes manual and i did follow it. You are forgetting however that standard line in the Haynes manual "refitting is the reverse of disassembly".

 

I suspect my key must be worn because it did go into the groove of the crank. i just didn't notice that it didnt go in all the way. a different key wouldn't go in the wrong way round at all.



#12 BaronVonchesto

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Posted 10 August 2019 - 01:47 AM

On on engine like this, there only needs to be 50% contact area on the Taper between the Crank and the Flywheel.

 

Looking at the Crank as is, I'd say cleaned up, you'd have close to 70%, but clean it up first.

 

this is a promising sign. I'll take the crank out and check with my local machine shop if he can weld and resurface it to fit a new flywheel boss. If the cost is similar to changing the crank then i'll just change the crank.

 

sigh... feels like all the effort from the past 2 months rebuilding the engine has been wasted...



#13 Rorf

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Posted 10 August 2019 - 04:54 AM

Cleaning that crankshaft taper will take a lot of meat off, then the interference fit in the flywheel boss will be lost. This part of the crank takes a fair amount of torque and weld building up is fine on journals but I would be hesitant to do that on the taper.

 

If it was me I would get another crankshaft, 998s are common enough.



#14 timmy850

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Posted 10 August 2019 - 05:51 AM

I was looking at my crank, flywheel, key washer and bolt this afternoon. I couldn’t fit the keyed washer in the other way, it just doesn’t fit as the key is offset to one side

#15 Moke Spider

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Posted 10 August 2019 - 06:05 AM

 

On on engine like this, there only needs to be 50% contact area on the Taper between the Crank and the Flywheel.

 

Looking at the Crank as is, I'd say cleaned up, you'd have close to 70%, but clean it up first.

 

this is a promising sign. I'll take the crank out and check with my local machine shop if he can weld and resurface it to fit a new flywheel boss. If the cost is similar to changing the crank then i'll just change the crank.

 

sigh... feels like all the effort from the past 2 months rebuilding the engine has been wasted...

 

 

 

Cleaning that crankshaft taper will take a lot of meat off, then the interference fit in the flywheel boss will be lost. This part of the crank takes a fair amount of torque and weld building up is fine on journals but I would be hesitant to do that on the taper.

 

If it was me I would get another crankshaft, 998s are common enough.

 

In cleaning it up, I'm not suggesting 'machining' it back at all, only taking off the high spots on what's there now.

 

While I did suggest doing it in a lathe, if you take your time, you could do it it in the bench. Starting with a 2nd cut file, taking probably only 4 or 5 strokes at the most to take off the highest spots, the finishing with a Diamond Lap from there. It will take a bit of time,but the diamond lap will really only take off the high spots.

 

Of course, if a replacement crank is easy and cheap enough, they would be the best and easiest option, however, I know with where you are what a 'struggle' it's been up to this point (financially), a repair might be the best option?

 

 

Regardless of how the repair is done, key to keeping these tapers in good order and workable is getting the flywheel on really tight. The damage you've done there is mostly from the flywheel fretting (basically rubbing) on the Taper of the Crank and for some time. That's what damages them.

 

When I fit these together, after a light lapping of them together, I lube up the taper with a very very like smear of 3 in 1 oil, then really heave down on the Flywheel Bolt, probably getting to 150 - 180 ft / lb. Under the extreme pressure exerted on the taper, the oil film breaks down and there's a good friction joint between the two parts - and no fretting ! You will need a good flywheel puller to get them apart, but you can be sure that the taper on both parts will be in perfect condition.






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