Sheared two crankshaft gears. Help Please.

[ross2006B7]

Hi Everyone.

Car is a B6 1.8 A4 2005. I'm rebuilding the bottom end and having some trouble with the crankshaft gear.

I have an APR bolt and have tried tightening it to the specified torque( i think it was 74fbs then a 1/4 turn using 30w oil).


Attempt 1: The engine was on a stand, I locked the flywheel, and torqued to 74, then got on it to do my 1/4 turn with a breaker bar. I heard a snap, the crank gear moved with the bolt but flywheel did not move. Check timing marks and sure enough, they were off.

Took off the gear - and the key fell out, sheared clean off. ( First gear on left / OEM one.) Crank still looked perfect at this point so I just ordered a new gear.


Attempt 2: Engine in-car mounted to trans and ready for the head to go on, just have to get this gear in and tighten it first (new OEM gear ordered from FCP euro, gear in the right on the picture. Locked the brakes, and put it in 5th, tightening the bolt until it shifted a bit and then couldn't get any more, maybe moved a little less than 1/4.

Thought it would be all good, then the timing didn't line up again. Pulled it off and then felt sick to my stomach as the crank now looks damaged - which happened loosening the bolt.


So my questions are : Can i just pin the crank with a new gear and be ok? and WHAT the hell is the best way of tightening this bolt without shearing another gear.


As always, thanks a ton and all the best,

Ross.

[KHARDa4]

My suggestion would be to use IE press fit timing gear but based on what i see i don't know if you can use that now. It could be worth a try to file down the flared edge and use the press fit gear but at that point you're gambling. Not something i would personally try myself, I would probably source a good used crank and rebuild it.

Sent from my SM-G955U using Tapatalk

[ross2006B7]

My suggestion would be to use IE press fit timing gear but based on what i see i don't know if you can use that now. It could be worth a try to file down the flared edge and use the press fit gear but at that point you're gambling. Not something i would personally try myself, I would probably source a good used crank and rebuild it.

Sent from my SM-G955U using Tapatalk

Appreciate the response. I'll probably get the gear. I'm dying not to tear this all out again so i may try that.

[Kevin C]

The crank will be fine. The keyway is to locate the sprocked and does not add that much to holding it. As long as a fully seated sprocket fits snugly, your good. What keeps the sprocket in place is the friction force from the nose of the crank to the back of the sprocket. How much friction you get depends on the clamping force to the bolt. That's why the torque procedure is so extreme. What I think is happening it that the friction between the bolt head and the sprocket is much higher than the friction of the sprocket to the crank nose, that causing the sprocket to rotate as you tighten. Lube under the bolt head and dry from the sprocket to the crank would help. I would also look at the bolt to understand why its turning the sprocket on the crank.

If it was my motor I would get a new sprocket and place a diamond washer from the 2.0T under it. That will increase the the pulley to crank friction by a factor of 3 to 4X. That will insure it assembles right and stays that way, I would also use a stock TTY bolt. That's all you need, 3X better than stock and way better than using the ARP bolt.

Do you have a picture of the underside of the ARP bolt head and the other side of the sprocket?

Diamond Washer:
https://www.ecstuning.com/b-genuine-...ch/06c105193b/

[ross2006B7]

Really appreciate the help, Kevin. I've attached the requested pictures. I was considering either going with the IE press-fit timing gear or to dowel pin the crank gear. Not sure if there is a professional opinion there, but leaning towards the dowels currently. The washer is great advice and I should have done that along with the oil on the back of the bolt head. And being I already have the ARP bolt, I'm hard-pressed to go buy another but if the consensus is that its necessary then I'll go that route. Thanks again!

[KHARDa4]

To each their own i guess. If i was building this engine to make serious power there is no way I would use that. To much to risk. I went down the big turbo built engine route and the OEM timing gear is trash, even pinned. I personally know a 1.8t local to me with a 2 pinned OEM timing gear that rotated away from the crank causing severe engine damage. The IE gear is the only way to go imo. Good luck with it.

Sent from my SM-G955U using Tapatalk

[ross2006B7]

Do you have a picture of the underside of the ARP bolt head and the other side of the sprocket?

Forgot to tag you in the post but I uploaded pictures you're looking for.

[Kevin C]

No problem. Thanks for posting the photos. Looking at the bolt and the pulley, I don't see anything obviously bad. This may be a lubrication issue causing the rotational friction under the bolt head to be much higher than the rotational friction from the pulley to the crank snout.


Increasing Strength:

To answer a few questions I ran some numbers.

What does just the center bolt do? I assumed 102000 N proof load for the crank bolt (22,930 lbs) , thats a grade 9.8 ,16mm bolt. Yes that's a lot of force! I also assumed a .7 coefficient of friction for steel on steel (dry non lube, may not be achievable) The ID of the thrust surface is 18mm and the OD is 34 mm (R=9, and R= 17).

Torque in Nmm: .7 * 102000 * 2/3*((17^3 - 9^3)/ (17^2-9^2))= 957491 Nmm or 958 Nm or 707 ft lb.

If a diamond washer is used the friction goes from .7 to 2.8 and the torque that the joint will hold is now about 2800 ft lbs.

Same case using lower friction values (oil on mating surfaces)

Assuming that the steel on steel is .2 (oil on the surface, pretty typical).

Then the joint holds 202 ft lbs. If you add a diamond washer to that you get 800 ft lbs.

Dowel Pins:

Most dowel pin setups are claiming to have 7200 lb sheer strength of the dowels. That appears to be 2 , 3/16" dowels. To sheer two dowels located at a radius of .433 " from the center of the crank would take 3100 ft lbs of torque.
One dowel would get you 1550 ft lbs.

In a perfect world that adds to the existing joint friction. Real world is a bit less forgiving. The problem is if the joint has any looseness and the pulley slips at the end of the crank snout the joint will see an impacts load. For the friction surfaces and the pin location to work together it all has to fit perfectly.

The problem with dowel pins is any slop greatly reduces how well they work and can lead to problem. You also don't get the ideal result since the walls supporting them are thin and will break first. Done right its a great solution, dont wrong it breaks easier.

As far as a press fit gear goes a .0008" interference fit would add about 220 ft lbs of torque capacity. Thats a really solid gain.

All are viable solutions. My preference for the diamond washer is its easy to install correctly. Pinning the pulley works but there is a lot more to go wrong. A press fit pulley is another solution that will work. Based on my calculations its more than enough but not as good as the washer solution and you have to deal with a press fit pulley.

The diamond washer fixed the same issue on the 2.0T motor, in that case the problem was the direct injection has a very fast pressure rise time and causes a lot more crank vibration. If that solution works on the 2.0T its more than enough for a port injection motor.

My other case for the washer is that your increasing the safety factor by a 4X from stock. If that doesn't work out have some other type of problem.

Summary:

Likely Root Cause: The original problem is most likely too much friction under the bolts head. It could be from loctite under one surface and oil under the other, surface finish or lube on the nose of the crank and dry under the bolt head.

I'm not convinced that the ARP bolt is a better solution and I really don't like that some instruction say that loctite is required. On the TTY bolts the biggest issue is getting them back out.

Feel free to check my calculations.

[Kevin C]

Also, ECS has the washers on sale for $22.

[ross2006B7]

One other thing that might help is to get a tool to hold the crank pulley as you tighten the bolt.

I've gone with your washer idea and the IE press fit gear. I'll clean up the back of the gear and its contact points, then lube the bolt head and I'll report back in a week here once the parts get in.

(Also I've looked at the tool I think..... are you referring to this - https://www.amazon.com/Elf-Bee-Crank...pe=all_reviews ).

Again, Thanks for all the effort put in with that post Kevin. It's much appreciated.

[KHARDa4]

Good job and info Kevin! All i knew was diamond washers held good, now I know why. I was working on a buddies Focus RS and was shocked to know there was no keyway on the timing gear. It was just held in place by a bolt with diamond washers. I also didn't know you could add them to our OEM timing gear or the FSI gear. I'm just worried if OP files it down for the pressfit gear to slide on the extra lip may not allow the gear to seat fully on the crank. Worth a try before getting a new crank. Good luck again OP!

Sent from my SM-G955U using Tapatalk

[KHARDa4]

Something else to know is the IE gear is precision made, there is no play to actually slide it on the crank. It has to be drawn on with the crank bolt. The crank has to be almost perfect for you to be able to do this.

Sent from my SM-G955U using Tapatalk

[Kevin C]

Something else to know is the IE gear is precision made, there is no play to actually slide it on the crank. It has to be drawn on with the crank bolt. The crank has to be almost perfect for you to be able to do this.

Sent from my SM-G955U using Tapatalk

I was also a bit worried about that. The keyway only looks to be damaged in the initial lead in, so once fully seated it will orient the pulley correctly. As you pointed out, its getting it initially aligned that could be a challenge (the Press fit IE part). In general the keyway is not intended to hold any force, just locate during assembly. Part of this is that the keyway has some slop, if the pulley moves within that slop then the surfaces will fail from fretting.

What fretting looks like:

[ross2006B7]

Thanks again guys for the input. Just to confirm. It's either the washer and OEM gear OR the press fit gear alone... is that correct. I would use both if it was advantageous.

I'll take a look when I get the press fit gear and weigh both my options at that time.

( I've emailed IE support and Dave (IE Sales) was unaware of the solution using the washer for this model and does not know if the press fit gear would work with it)

[Kevin C]

There is no reason the press fit cant be used with the washer. The issue I'm concerned with is getting the press fit gear on with a slightly damaged keyway on the crank.

[EuroxS4]

Stock crank gear is made of swiss cheese/very weak. Press fit gear is the way to go however with damaged crank the results may be similar. Need to have a good solid crank to start with. Also using a ekagrip diamond washer will probably help also ad torqing it to the proper almost impossible spec.

[Kevin C]

Stock crank gear is made of swiss cheese/very weak. Press fit gear is the way to go however with damaged crank the results may be similar. Need to have a good solid crank to start with. Also using a ekagrip diamond washer will probably help also ad torqing it to the proper almost impossible spec.

A few posts up I ran a couple calculation on using a diamond washer:

Center Bolt Clamping Force: Assuming a 102000 N proof load for the crank bolt (22,930 lbs) , thats a grade 9.8 ,16mm bolt. Yes that's a lot of force! I also assumed a .2 coefficient of friction for steel on steel

Torque in converted to ftlbs : .2 * 102000 * 2/3*((17^3 - 9^3)/ (17^2-9^2))= 270 Nm ~ 200 ft lb.

If a diamond washer is used the friction goes from about 4 X and the torque that the joint will hold is now about 800 ft lbs.

Also I don't think the pulley is made of swiss cheese. If that's was the case then yes it's probably no gouda; I actually think its made of powdered metal.

[EuroxS4]

A few posts up I ran a couple calculation on using a diamond washer:





Also I don't think the pulley is made of swiss cheese. If that's was the case then yes it's probably no gouda; I actually think its made of powdered metal.

Trust me swiss cheese with lots of air pockets. I love swiss cheese It makes me money!!! LOL Do it once and do it right and forget about it.

[Kevin C]

Trust me swiss cheese with lots of air pockets. I love swiss cheese It makes me money!!! LOL Do it once and do it right and forget about it.

Your saying you have seen stock 1.8T crank sprockets with air pockets in them that were large enough to be visible without magnification?

[ross2006B7]

Hey, just wanted to finish this off. I used the press-fit gear, the washer you recommend, ARP bolt, and counter holding tool.

I cleaned up the crank after filing my mistake down a bit and made sure the crank and gear contact areas were oil-free. Slowly pulled on the press-fit gear and washer with an impact to get it in place, (slid perfectly level all the way down at an even pace with no snags). Backed out the bolt(added some oil to the head) then torqued it to 74lbs, then with the counter holding tool, was able to safely get my extra qtr turn no problem this time.

Timing all lined up..fingers crossed it all holds.

Thanks again for the help

[KHARDa4]

Hey, just wanted to finish this off. I used the press-fit gear, the washer you recommend, ARP bolt, and counter holding tool.

I cleaned up the crank after filing my mistake down a bit and made sure the crank and gear contact areas were oil-free. Slowly pulled on the press-fit gear and washer with an impact to get it in place, (slid perfectly level all the way down at an even pace with no snags). Backed out the bolt(added some oil to the head) then torqued it to 74lbs, then with the counter holding tool, was able to safely get my extra qtr turn no problem this time.

Timing all lined up..fingers crossed it all holds.

Thanks again for the help

Glad it worked out for you bud. Those press fit gears are damn near bullet proof. I was spinning to 8500 with no issues or concerns of it breaking.

Sent from my SM-G955U using Tapatalk

[hightime80]

Your saying you have seen stock 1.8T crank sprockets with air pockets in them that were large enough to be visible without magnification?

Lol. I think u smell the samething i do 💩

[KHARDa4]

I think he's referring to his comment of swiss cheese and how it has air pockets in the cheese. He doesn't actually mean there is air pockets in the metal, just how weak of a gear it is. At least that's how i took it.

Sent from my SM-G955U using Tapatalk