Mi16 - Hit 3Rd Gear By Mistake At 110Mph :(

[SweetBadger 94]

So we were supposed to be racing at Donington Park last weekend, but it wasn't to be...

 

We went on a track-day the day before and all was going well - it's a fantastic track. Just before the end of the day my team mate when to shift from 4th to 5th @7600rpm (110mph) and hit 3rd.

 

I've worked out the engine probably hit 9200 rpm momentarily, the clutch was dipped very quickly, amazingly the engine seemed fine and my team mate continued for another half a lap with no obvious signs of an issue... Then the engine just died - no power and backfiring.

 

We couldn't work out what was wrong - cam timing measured up ok, compression a little down on one cylinder by not enough to stop it running. In the end we suspected the ECU as the engine would crank over with compression but was popping and banging out of the throttle bodies - so we had to miss the race and get it back home . Plugged in laptop when I got home and all seemed fine with the ECU so still a mystery...

 

I tried starting it again on Monday, and all of a sudden the engine stopped rotating and there was a horrible grumbling noise - the flywheel was spinning without the rest of the engine!

 

I think the flywheel bolts went, and then the flywheel friction welded itself to the crank in the wrong place hence the timing being off!

 

 

See below pics:

 

 

I'm a little worried about the state of the crank flange, the most damaged side of it is shown below:

 

 

 

It's taken a right hammering!

 

I should be ok removing the bolts and dowel - the dowel is only case hardened so I'll drill and tap it for an M6 bolt then pull it out, but I'm a little concerned I won't get the flywheel exactly centred due to the damage to the end of the crank.

 

I put the damaged flywheel back on without the locating dowel in place to see how much movement there was - in one axis there was none, but in another there was about 0.5mm.

 

Am I right in thinking that once the bolts are done up it's the friction between the flywheel and the crank that takes all the drive force? In which case it doesn't rely on a super tight fit between the flywheel and the locating flange on the crank? If so with the dowel replaced I think we'll get away with it.

 

My plan is to get a TTV lightened flywheel fitted while the box is off and see how we get on - it'll be pretty obvious if something's amiss due to vibrations. Looks like the engine will be going for a rebuild at the end of this season so I can get my spare crank in it, but I don't want to miss the last race of the season at Oulton Park...

 

What a pain! To be honest I'm quite impressed there's no apparent internal damage to the engine after it hit such high rpm (MI16 on stock internals and valve train this uprated cams so very little piston-valve clearance!)

[welshpug 1,657]

ive done 5th to 2nd in an 8v and did the same to the bolts and dowel, no damage at all to the crank though in my case.

 

I doubt youll be able to drill the dowel, I welded a bolt to it and pulled it out, most of the bolts wound out with grips iirc.

[SweetBadger 94]

I read the post you put up when this happened to you Welshpug as I was wondering how common this is. 5th to 2nd! Blimey that must have been a shock!

 

I've already tried drilling the sheared off bit of dowel and my cheap screwfix drill bits in a battery drill went straight through it no problem, so I think it'll be ok:

 

 

 

When I got through the other side and hit the case hardening it ruined the bit mind.

 

 

Mostly concerned about the damage to the crank (and potential internal damage to engine, although it ran happily for half a lap afterwards so fingers crossed its ok).

[calvinhorse 870]

Bloody hell!! You'd think the clutch would slip before it did damage like that.

[petert 586]

Unlucky. You'll still need to strip it entirely and check for piston smacks.

[Tom Fenton 1,541]

Whoops. I think that crank is toast from that picture. If the flywheel isn't perfectly centred on that spigot on the end then the thing will vibrate like hell, you may as well put square wheels on!

[petert 586]

And always look on the bright side of life. Treat it as an opportunity to add more compression, better valve seat area, increased capacity etc.

[SweetBadger 94]

Ahh balls! It would be nice to look at this as an opportunity to improve the engine, but I don't need to as the series we race in classifies cars on power / weight and we're right on the limit of a class boundary - if we had more power we'd just have to add ballast. I guess more low down torque would be nice, but to be honest we never had any complaints about the power delivery...

 

It looks like it's going to be a case of swap the crank in-situ and hope for the best - very unlikely I'm going to have time to build a new engine for it before Oulton... The engine has been living on borrowed time anyway after the ordeal with the threads pulling out of the block, and all the fancy expensive bits are bolt on and can be transferred to another engine easily enough if it does let go.

 

Will get a bore scope on it to check for any obvious signs of piston-valve contact.

[dcc 855]

You need an xud crank!

[SweetBadger 94]

 

Good news! Replacement crank in, new lightened flywheel on, and it lives again!

 

Once the lifters refilled the top end in nice and quiet so think fingers crossed that's it sorted.

 

Bloody annoying though - the old crank and bearings came out really clean with no signs of wear :-(