General: 850: - crossed threads?

donal · Mar 15th, 2007, 15:59

I think that I may have crossed the threads on one of the inlet manifold bolts (which I think is an M7). I started to do it up and then undid it a few times in an effort to get it to on the right thread, yet I couldnt seem to get it to thread freely. It seemed to be getting tight too soon. Anyway, eventually I tightened it up but it seemed to require a lot more torque than the others to do up. Even now there is a tiny gap btween the head of the bolt and the manifold. I am concerned that if I do it up more that it will strip.
As it stands the car runs perfectly. Maybe I should just leave it alone. The problem could be down the line if I need to do some other work on the engine at some stage and I need to undo this bolt. At that stage I guess I could try some Loctite "form a thread".
If that didnt work could I use a tap and create threads for an M8 bolt?

Any suggestions?

Georgey dee · Mar 15th, 2007, 16:34

Hmmmm,
Difficult one, do you leave it or try and fix it?? I would whip it out and inspect the threads and then wind a thread tap of the correct size down the thread. Remember that they're only 20 Nm each so don't swing off them.

I always opt for new bolts when I do engine work, they're only pennies and they save pounds.

donal · Mar 15th, 2007, 16:43

Thanks,

The threads on the bolt are fine. It did notice a tiny fragment of aluminium when I took it out - I assume this is from the head.

jimathan · Mar 15th, 2007, 16:46

Assuming it is M7, buy a no1 tap and run it down all the way with the manifold in place. (That will help guide the tap) This should cut out any crossed threads, thus back to how it should be. If the bolt lets go when you tighten it up, you could tap out to M8 but you will have to drill the manifold 8.5mm for clearance. The proper way would be to remove the manifold and fit a helicoil. This is a permanent repair but not that cheap, as a helicoil kit consisting of oversize tap, insertion tool, drill and helicoils may cost around £20-£25.

demonicwillow · Mar 15th, 2007, 18:00

Im a marine engineer and genuine Volvo Penta engines and drives are actually helicoiled from new so saves alot of problems in a few years, but I dont know about just Volvo, chances are bolt or stud holes have been helicoiled from new.

dmw

donal · Mar 15th, 2007, 18:26

Thanks, good suggestions.

Do you know if the bolthole in the head goes all the way through the head wall, or does it bottom out?

donal · Mar 15th, 2007, 18:31

Quote:

Originally Posted by jimathan

Assuming it is M7, buy a no1 tap and run it down all the way with the manifold in place. (That will help guide the tap) This should cut out any crossed threads, thus back to how it should be. If the bolt lets go when you tighten it up, you could tap out to M8 but you will have to drill the manifold 8.5mm for clearance. The proper way would be to remove the manifold and fit a helicoil. This is a permanent repair but not that cheap, as a helicoil kit consisting of oversize tap, insertion tool, drill and helicoils may cost around £20-£25.

Did you mean 7.5mm?

Mar 15th, 2007, 18:44

The bolts are M8, I think.

Incidentally, I did exactly the same thing when I replaced my own breather system! The third top manifold bolt refused to go back straight no matter how many times I tried to correct it.

It still tightened securely and clamped the manifold firmly so there is no need to mess with it. Unfortunately, in my particular case, it has to come out again (when the weather's nice), as I later realized I'd connected two of the breathers the wrong way around on the separator!

donal · Mar 16th, 2007, 08:56

thanks stuart.

pity you have to take it off again. at least it should be a bit easier the second time around. let me know how you get on with that bolt.

the problem is, if the manifold has a vacuum leak the engine will not idle properly. perhaps it will seal without that particular bolt. then again maybe you will be able to do it up again. failing that as the other posts have indicated, you can re-tap the threads or tap to a bigger size bolt.

Mar 16th, 2007, 22:07

It seals fine. I know this because it's ran fine since it went in in January

I won't be re-doing the job until some nice weather comes, since having the pipes swapped isn't so serious, it just means the oil vapours won't be trapped as effectively.

Remember that it's the gasket that provides the seal, and the bolt is clamping the manifold tightly to it, despite being crossed, so there's no problem (at least until I disturb it again

).

Mar 15th, 2007, 15:59	#1
donal Member Last Online: Jan 4th, 2013 12:56 Join Date: Sep 2006 Location: Athlone Town, Ireland	crossed threads? I think that I may have crossed the threads on one of the inlet manifold bolts (which I think is an M7). I started to do it up and then undid it a few times in an effort to get it to on the right thread, yet I couldnt seem to get it to thread freely. It seemed to be getting tight too soon. Anyway, eventually I tightened it up but it seemed to require a lot more torque than the others to do up. Even now there is a tiny gap btween the head of the bolt and the manifold. I am concerned that if I do it up more that it will strip. As it stands the car runs perfectly. Maybe I should just leave it alone. The problem could be down the line if I need to do some other work on the engine at some stage and I need to undo this bolt. At that stage I guess I could try some Loctite "form a thread". If that didnt work could I use a tap and create threads for an M8 bolt? Any suggestions?

Mar 15th, 2007, 16:34	#2
Georgey dee Premier Member Last Online: Feb 14th, 2024 18:36 Join Date: Dec 2005 Location: Norwich View Photos By: Georgey dee	Hmmmm, Difficult one, do you leave it or try and fix it?? I would whip it out and inspect the threads and then wind a thread tap of the correct size down the thread. Remember that they're only 20 Nm each so don't swing off them. I always opt for new bolts when I do engine work, they're only pennies and they save pounds. __________________ HAD; 440 GLT(Loved it), 850 GLT auto(Loved it), S70 2.5T(Nothing but problems!), 850R auto(Loved it!!), S60 D5 SE (Nothing but problems!) GOT; S60 D5 SE Lux Auto RAF Marham Track Day Co-Ord'

Mar 15th, 2007, 18:00	#5
demonicwillow yer-tis ! Last Online: Aug 16th, 2008 12:46 Join Date: Mar 2007 Location: Bridgend View Photos By: demonicwillow	Im a marine engineer and genuine Volvo Penta engines and drives are actually helicoiled from new so saves alot of problems in a few years, but I dont know about just Volvo, chances are bolt or stud holes have been helicoiled from new. dmw __________________ I used to be a kleptomaniac .... now I'm taking something for it .. PS, If you go any slower, you'll pass yourself on the way back!!

Mar 15th, 2007, 16:43	#3
donal Member Last Online: Jan 4th, 2013 12:56 Join Date: Sep 2006 Location: Athlone Town, Ireland	Thanks, The threads on the bolt are fine. It did notice a tiny fragment of aluminium when I took it out - I assume this is from the head.

Mar 15th, 2007, 16:46	#4
jimathan Senior Member Last Online: Feb 21st, 2023 16:01 Join Date: Mar 2007 Location: blackburn View Photos By: jimathan	Assuming it is M7, buy a no1 tap and run it down all the way with the manifold in place. (That will help guide the tap) This should cut out any crossed threads, thus back to how it should be. If the bolt lets go when you tighten it up, you could tap out to M8 but you will have to drill the manifold 8.5mm for clearance. The proper way would be to remove the manifold and fit a helicoil. This is a permanent repair but not that cheap, as a helicoil kit consisting of oversize tap, insertion tool, drill and helicoils may cost around £20-£25.

Mar 15th, 2007, 18:26	#6
donal Member Last Online: Jan 4th, 2013 12:56 Join Date: Sep 2006 Location: Athlone Town, Ireland	Thanks, good suggestions. Do you know if the bolthole in the head goes all the way through the head wall, or does it bottom out?

Mar 15th, 2007, 18:44	#8
stuartsharp Guest Location:	The bolts are M8, I think. Incidentally, I did exactly the same thing when I replaced my own breather system! The third top manifold bolt refused to go back straight no matter how many times I tried to correct it. It still tightened securely and clamped the manifold firmly so there is no need to mess with it. Unfortunately, in my particular case, it has to come out again (when the weather's nice), as I later realized I'd connected two of the breathers the wrong way around on the separator!

Mar 16th, 2007, 08:56	#9
donal Member Last Online: Jan 4th, 2013 12:56 Join Date: Sep 2006 Location: Athlone Town, Ireland	thanks stuart. pity you have to take it off again. at least it should be a bit easier the second time around. let me know how you get on with that bolt. the problem is, if the manifold has a vacuum leak the engine will not idle properly. perhaps it will seal without that particular bolt. then again maybe you will be able to do it up again. failing that as the other posts have indicated, you can re-tap the threads or tap to a bigger size bolt.

Mar 16th, 2007, 22:07	#10
stuartsharp Guest Location:	It seals fine. I know this because it's ran fine since it went in in January I won't be re-doing the job until some nice weather comes, since having the pipes swapped isn't so serious, it just means the oil vapours won't be trapped as effectively. Remember that it's the gasket that provides the seal, and the bolt is clamping the manifold tightly to it, despite being crossed, so there's no problem (at least until I disturb it again ).

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)