Sheared Bolts

[stownsend]

Hi

I've got an AQ151 with 290 leg. Did some work on the exhaust manilfold Sat afternoon, started her up and tweaked the carbs. Went to restart her and the startermotor is turning the fly wheel but nothing else is turning, found all 8 bolts on the flywheel to crank had sheared. Any ideas why it may have happened ?

I've been refurbishing the boat and engine, have just rebuilt it. The bolts were the orginal ones so may be weaker and could have been loose.

The engine and boat (since I'd bought them) are yet to see the water, I was hoping to launch in 6 weeks but thats a bit behind now !

Would drill out and replace be the best option ?

Cheers

Stu

 

[DavidJ]

Most unusual. The force required to shear 8 bolts is far more than a starter motor can deliver. I can only think that the bolts have corroded (by salt water) to such an extent that they have been weakened.
When you replace the bolts make sure you use high strength ones. There are rings on the bolt head to tell you the strength (your car Haynes manual usually has a page on it)
I bet the studs left in are well rusted so plenty of blowlamp heat and lubricant like 'plus gas' and plenty of luck. Maybe resign yourself to drilling out and retapping the next size if that's possible.
ps I'm selling a Beetle ...wanna buy one!!
http://cgi.ebay.co.uk/2001-Volkswag...ewItemQQptZAutomobiles_UK?hash=item1c10b592c3

 

[stownsend]

Below are the pics of the damage, got off lightly, just have to work out the best way to remove the studs.

Cheers

Stu

 

[sarabande]

it looks to me as if they all been sheared by sequential failure, which would probably for the deep gouges in the adjacent metal and at the shoulder of the thread.

 

[jfm]

Hi

I've got an AQ151 with 290 leg. Did some work on the exhaust manilfold Sat afternoon, started her up and tweaked the carbs. Went to restart her and the startermotor is turning the fly wheel but nothing else is turning, found all 8 bolts on the flywheel to crank had sheared. Any ideas why it may have happened ?

I've been refurbishing the boat and engine, have just rebuilt it. The bolts were the orginal ones so may be weaker and could have been loose.

The engine and boat (since I'd bought them) are yet to see the water, I was hoping to launch in 6 weeks but thats a bit behind now !

Would drill out and replace be the best option ?

Cheers

Stu

It's a complete myth to talk about bolts like that taking shear loads. If assembled properly, they should be loaded in tension only. Friction between the two components, created by the bolt tension, should take the shear load. The reason these bolts failed could be that they were not tightened up enough so that they were actually loaded in shear, which they shouldn't ever have been. Also fatigue (from spending too much of their life not tightened enough, which increases the stress amplitude hence the fatigue cracking) and corrosion might have contributed. Bolts must be tightened properly else you do all sorts of damage to them. It's a completely wrong to tighten them only modestly so as "not to strain them too much" as you see some fitters or amateur engineers doing

You can get a stud extractor to remove the studs. They need care but will work. Tool suppliers like Axminster sell them

 

[Heckler]

I would get a pin punch and start tapping gently on the remnants, I would bet that they come out pretty easily. Been there done that many times.
Stu

 

[Bilgediver]

Hi

I've got an AQ151 with 290 leg. Did some work on the exhaust manilfold Sat afternoon, started her up and tweaked the carbs. Went to restart her and the startermotor is turning the fly wheel but nothing else is turning, found all 8 bolts on the flywheel to crank had sheared. Any ideas why it may have happened ?

I've been refurbishing the boat and engine, have just rebuilt it. The bolts were the orginal ones so may be weaker and could have been loose.

The engine and boat (since I'd bought them) are yet to see the water, I was hoping to launch in 6 weeks but thats a bit behind now !

Would drill out and replace be the best option ?

Cheers

Stu

You mention studs?????? What we see are bolt heads and bolt heads threaded to the head as well!!!!! Are they marked B and Q

You will note that there are thread indentations in the flywheel holes which suggests that the flywheel has been allowed to run loose and the cyclic torsional vibrations on the crankshaft have done exactly what one would expect and sheared the bolts.

You say the boat has not seen the water. Did you buy the boat like this or did you replace the bolts.?

These are critical bolts on a very critical connection where a lot of forces come into play and the bolts that were there certainly do not seem to be what would be expected though Volvo Paul may comment further.

I would expect the correct bolts to be only partially threaded so that there is a threadless portion of the bolt in the holes in the flywheel and these bolts should be a good fit in the flywheel. Moreover the two mating surfaces should
be smooth and also a good fit with each other.

The bolts will no doubt be high tensile and in fact the correct bolts may be Allen bolts as on a Bukh and other engines and must be tightened to the correct torque.

 

[stownsend]

The bolts were the orginal ones, looking at the manuals they look like the correct ones. The boat has been a project, Invader 2200, the engine and leg come from a speed boat (the next project but that will be converted to take an outboard).

I've got a couple things to try over the weekend, and a extractor set is on order !

Cheers

Stu

 

[Heckler]

JFM mentioned studs, irelevant anyway, bottom line, get the broken bits out, whatever they are called. Allen screws, a red herring, as the man says they are original.
Stu

 

[GrahamHR]

Something in the pics looks odd to me; threaded holes in the end of the crank (pic 1, normal) with the remains of bolts, with the holes in the flywheel also threaded ( pic 2)? Strange indeed. Every flywheel/ crank assembly I have come across has threaded holes in the crank ( sometimes with additional dowels) with plain holes in the flywheel. If both the flywheel and crank holes were threaded, there's no chance of correct ( long lasting) assembly.

Graham

 

[Bilgediver]

Something in the pics looks odd to me; threaded holes in the end of the crank (pic 1, normal) with the remains of bolts, with the holes in the flywheel also threaded ( pic 2)? Strange indeed. Every flywheel/ crank assembly I have come across has threaded holes in the crank ( sometimes with additional dowels) with plain holes in the flywheel. If both the flywheel and crank holes were threaded, there's no chance of correct ( long lasting) assembly.

Graham

If you look carefully at the holes in the flywheel you will see that those apparent threads are actually indentations caused by the threaded portion on the bolt impacting . The holes are only marked on two sides with the inner and outer part of the hole showing the correct plain surface.

This impact damage was probably caused when the bolts came loose and the flywheel started to oscillate on the flange due to torsionals and then sheared the studs.

Volvo have had problems with these bolts and studs on other engines. They need to be correct and tightened correctly. I am checking out a manual tomorrow.

 

[GrahamHR]

I didn't spot that feature (obviously!). Unless the bolts have been bottomed in the holes in the crank, shouldn't their remains be rather loose? Maybe the bolts were too long, bottomed in the crank then the flywheel was on the edge of being loose?

Graham

 

[Bilgediver]

I didn't spot that feature (obviously!). Unless the bolts have been bottomed in the holes in the crank, shouldn't their remains be rather loose? Maybe the bolts were too long, bottomed in the crank then the flywheel was on the edge of being loose?

Graham

I suspect the bolts can screw right through the flywheel flange...Will be looking at a manual tomorrow so can comment after.

 

[jfm]

JFM mentioned studs, irelevant anyway, bottom line, get the broken bits out, whatever they are called. Allen screws, a red herring, as the man says they are original.
Stu

WTF? I did indeed say "studs" and I was perfectly correct. A bolt with the head broken off is a stud, and the tool you buy to deal with it is a stud extractor. Go and learn some engineering before mouthing off

 

[jfm]

They need to be correct and tightened correctly.

Exactly! The bolts (actually they're screws if we're being pedantic) must be tightened to the correct spec so that they are loaded in tension only, not shear. This ensures they endure little or no stress cycling and hence little or no fatigue

 

[burgundyben]

Exactly! The bolts (actually they're screws if we're being pedantic) must be tightened to the correct spec so that they are loaded in tension only, not shear. This ensures they endure little or no stress cycling and hence little or no fatigue

If we are being pedantic I'd say they are 'hex head machine screws'...if metric they should say 8.8 or 12.9 on the head, that describes the tensile strength of the bolt.

Looking at the mating face of the crank and flywheel I think getting that flywheel secure on the crank is going to be more problematic than removing the broken remains of the hex head machine screws (!), As JFM describes earlier, the force applied between the mating faces by the tension in the hex head machine screws (!) causes the friction that holds the two together.

The mating faces appear rather mashed up in a couple of areas, no doubt caused by the jiggling around when loose, I reckon its been brewing for sometime. In a way its a pity its not friction welded itself together (although longer term that might be more of a mare to deal with).

Its hard to tell from the pics how bad the surfaces are.

If the damage to the surfaces is minor then a good lapping with grinding paste might clean it up enough for it to keep hold. Subject to visual inspection I'd say that was my first route forward.

If that fails we're into some machine shop work. Oh heck.

 

[jolly abseilor]

hi, in an attempt to remove the sheared studs out of the flywheel, i would go for the following;
1st and formost cover the bearing up in the centre, to protect it from any metal debris.
2nd centre pop the centres of each stud the nearer the centre the better.
3rd obtain a stud extractor and the relevant drill bit.
4th with patience and care drill the stud out
5th use the extractor to remove the broken stud.
patence is definately required but should come out fairly easily, this assuming that when you put the bolts in, tension was on the bolt head and washer and that you didnt bottom out the 'thread side of the bolt'.

best of luck
jon

 

[Bilgediver]

I
Its hard to tell from the pics how bad the surfaces are.

If the damage to the surfaces is minor then a good lapping with grinding paste might clean it up enough for it to keep hold. Subject to visual inspection I'd say that was my first route forward.

If that fails we're into some machine shop work. Oh heck.

I was also going to comment on this after looking at the manual. Yes those are the correct bolts if of the right tensile and only need 52 lbs ft torque however this is dependant on a good mating surface on the crankshaft and the flywheel.

Volvo say the runout must not exceed 5 thou so to achieve this on the face of the flywheel the OP might have to at least find a friend with access to a lathe big enough to swing the flywheel and clean up and true up the mating face.

HE might need to deal with the crankshaft with an oilstone to restore flatness. It is certainly not worth bodging back the flywheel without restoring the machined flatness or this will become an ongoing project. It the runout exceeds Volvos figures then the bolts will experience excessive cyclic loadings and probably fail again .

 

[stownsend]

Looks like I'm going to have a busy few days !

Thanks for all the help, I'll let you know how I get on.

Cheers

Stu

 

[Heckler]

WTF? I did indeed say "studs" and I was perfectly correct. A bolt with the head broken off is a stud, and the tool you buy to deal with it is a stud extractor. Go and learn some engineering before mouthing off

Hey, wind the neck in! The poster was intimating I said studs, there was no criticism of you! I was correcting his mistake!
Stu