Mi16 Head Bolt

[jas-E 1]

hey guys,

 

Was about to finish my mi16 rebuild, but have come to a complete stop. I was putting the head back on last week and got new head bolts from QEP. i followed the tightening sequence as i found on the forum, and the 9th bolt to tighten (thats the one on the flywheel end) was being an arse to turn by 300 degrees. Every other bolt torqued up without any problems but this one was being a pain past about 220 degrees. (I was building the engine with someone who has been working on engines for about 20 years, and even he said it dint feel right!!). I changed the bolt with the one in the 10th hole, and it was still the same. Used an older bolt and it felt like it would snap past about 230 degrees. So decided i should leave it at that.

 

I got warned that if i leave it, it will come and haunt me later, so decided to act on it. The thread is a non standard one so having a hard time finding a tap for it that would also be long enough to fit thru the head, so just cut out some ferrels on an older bolt and past it through just so it was finger tight, and it came out with a little bit of swarf on the end. So the machinist suggested that if we shorten the bolt by about 3-4mm, and then try it might be ok to get to 300 degrees because it wont go as far as whatever was stopping it from being torqued. So shortened an older bolt, and started the tightening sequence, and at about 270degs, it went SNAP!!!

 

thought i had snapped a bolt but it wouldnt just pull out!! so undid it, and the threads from the crank case came out at the end of the bolt!!!there was no sign of any swarf in there, and no one at work knows why it wouldnt torque up and why it pulled the threads out!!!!!no i have a head on an engine with everything torqued up, and one bolt hole with no threads!!!

 

Is there any proper fix anyone can recommend??i dont mind removing the head - iv convinced myself that its not a bad thing as long as i know what to do with the head..!!can i use a helicoil in there??would it hold the pressure? or maybe there is enough space in there to fit an insert?? Any suggestions will be greatly appreciated...!!

 

Sorry for the extra long post, tried to shorten it as much as i could!!

 

thanks for all your help guys

 

Jas

[pug_ham 242 3 Cars]

It sounds like you have stripped the block.

 

There isn't anything at the bottom of the thread hole stopping the bolt is there?

 

You'll have to take the head back off but you can get the block helicoil with a stainless steel insert but if you are doing one I'd get them all done at the same time.

 

When I next rebuild an XU alloy block I'm seriosuly considering getting this done as an extra safety measure just to avoid instances just like this.

 

Graham.

[jas-E 1]

hey Graham..

 

I checked and even passed through some m8 studding to see if there was anything blocking the hole, and there wasnt!!its strange i tell you. I have removed the head now and have taped up the whole crank case bar the holes to prevent anything from falling in.

 

Im taking it to a local engine builder that did my cylinder head. Hopefully he will be able to come up with an explaination!! and like you said, might just get him to sort out all the threads while he is at it - if it doesnt cost too much!!

 

Since i have had the new bolts all torqued on the head, and now i have removed them, is it ok to re use them now??

 

thanks for your reply mate

 

Jas

[taylorspug 7]

It almost sounds like there is something in the hole that is stopping the bolt from tightening down, as Graham has said. Seeing as the made up tap went down with relative ease (im assuming), it must be a fundamental issue with the head bolts bottoming out on something? Sounds really weird anyway...

[rapidmi 4]

helicoils the way to go mate

[jas-E 1]

we didnt take the tap - well an older bolt with a ferrel on it right through because though tit would be better if we shortened a bolt and got it right first time. But it pulled the threads at 270degrees!

 

I was thinking of a helicoil, but we werent sure if they would be good enough to with stand the pressure a headbolt goes through..or the torque pressure that would be applied to it.

 

Any thoughts??

[ORB 227 1 Cars]

I had this very problem on a K-Series I was working on for a friend.

 

When I eventually got him to agree to let me pull the whole engine out and strip it down to inspect, it turned out to be a snapped head bolt that was left in the block from a previous H/G change.

 

There was about 10mm of the end of an old bolt left in the bottom of the block holes. I only worked it out when I got the old head bolts out of the bin to see that one had been cut down by about 15mm.

 

I could not get the leftover bit out, I gave the block to a friend who is very clever with this sort of thing, and he got it out for me.

 

I hope this is not the case for you as it is a complete bitch to sort out!

[pug_ham 242 3 Cars]

I was thinking of a helicoil, but we werent sure if they would be good enough to with stand the pressure a headbolt goes through..or the torque pressure that would be applied to it.

 

Any thoughts??

A helicoiled thread done proerly will be amazingly strong, far stronger than the threads cut into the alloy block originally imo.

 

They use helicoils on aircraft engines & various other high stress areas with no issues so it will be fine on a car engine. The tighter the threads are done up to more the helicoil insert grabs into the block.

 

Graham.

[DamirGTI 329]

Hi !

 

I feel your pain I've had same problem this year when i was rebuilding my engine (one major rusty head bolt has snapped when i was untightenig the head bolts in order to remove old head - was snapped deep inside the block and it was a big F****G nightmare to pull him out - anyway i could not do that it was so rusty inside almost as it was welded with the block surface so i have to scrap the block )

 

And also I've had one time snapped head bolt during that silly 300deg. tightening of the head bolts (it was new bolt not old one reused..)

 

From that time I'm using this method of tightening , rather than using scary 300deg. i do that this way :

 

1stage - 30Nm

2stage - 55Nm

3stage - loosen each bolt one at a time 1/8th turn and retighten to 55Nm

4stage - 80Nm

5stage - 101Nm (75lbf ft)

 

and after that , next day i do the final 'settle' - undone each bolt not more than 1/4 turn and then retight back to 101Nm (75lbf ft)

 

Cheers !

Damir

[jas-E 1]

thanks for that Damir

 

S should i scrap the recommended way of tightening the headbolts and just use this method? I didnt do all the 300 degrees at one time. I did them 100 degrees at a time so guess wasnt that bad. And this was the only one i had trouble with.

 

I had ot sorted by the way. Guy down the road charged me £70 because it took him one and a half hours to helicoil it!!something about making extensions. Had to be paind in the end i guess.

 

Thanks for all the help guys

 

Regards

 

Jas

[pug_ham 242 3 Cars]

Did you get them all helicoiled or just one?

 

Graham.

[jas-E 1]

Hey Graham,

 

I just got the one thread helicoiled..!!Was thinking that if he was going to charge me a tenner id have them all done, but £70 is a little steep for me!!

 

Anyway i have put the head back on and it tightened up perfectly..

 

Thanks again