1.9 Mi16 Alternator Tensioner Screw Thread Pitch

[jackherer 543]

I'm trying to properly sort out the alternator tensioner on my Mi16 engine, for a while it has just had a normal bolt so I've had to lever the alternator manually then tighten the bolt while holding the alternator in position which is getting boring now.

 

 

Number 3 is still available from Peugeot so I bought a new one, the long screw (number 2) is NFP but according to Service Box it is just an M8x1.25 screw.

 

However the thread in the tensioner (number 3) that I have here (that was in a sealed Peugeot bag) is definitely NOT M8x1.25. If anything it looks coarser but M8x1.5 seems to be extremely obscure so I don't think it is that.

 

I've done a bit of searching and I found this thread which sounds like the same problem - http://forum.205gtidrivers.com/index.php?showtopic=128455

 

Can anyone who has an Mi16 alternator tensioner to hand let me know what the thread of the screw is?

 

If it is meant to be M8x1.25 as it is labelled I'll try running a tap down it or something but as it is a brand new part I want to be sure.

[welshpug 1,657]

can't imagine it being anything other than 8x1.25.

 

8v one is 6x1.0, other stuff like TU and xu10 is 8x1.25 also.

[jackherer 543]

I agree but it definitely isn't!

 

I can wind an M8x1.25 nut onto the male part of the tensioner and I have plenty of M8 x 1.25 screws that also wind into the same M8x1.25 nut but none of them will go into the female part of the tensioner.

[Miles 331 1 Cars]

Yes it's not a normal pitch, never got around to finding out what it is thou

[jackherer 543]

Cheers Miles, it's good to know it's not just me, especially as servicebox says it is just M8x1.25!

 

I'll try my local fastener specialist tomorrow, and I'll post the result here.

 

The only thread I can find in theory that is approx. 8mm dia. and a slightly coarser pitch than M8x1.25 is 5/16" imperial which would be very surprising...

[JeffR 51]

Definitely 8 x 1.25 pitch. It's the angle of the threads which differs from a standard M8 x 1.25 bolt.

 

Edited August 5, 2017 by JeffR

[Tom Fenton 1,541]

Interesting one, I've noticed before that its a strange looking thread but never investigated further. Is it a twin-start thread so it screws in and out "faster" for the pitch?

[petert 586]

Aye. Lead = pitch x number of starts

[jackherer 543]

Thanks for that, very interesting indeed. I've seen twin start self tappers for steel sheet and wood before but I wouldn't have even thought of it in this context.

 

Suffolk Fasteners are closed today so I'll see what they can do on Monday.

 

I've now remembered having this problem in the past, on one occasion I just assumed the threads were damaged so I drilled them out and fitted an M8 helicoil which worked fine so it raises the question why did Peugeot use such an obscure screw thread for something as simple as an alternator tensioner?

[Tom Fenton 1,541]

I wouldn't hold much (read: any) hope of buying a twin start m8 off a shelf. You could have one made but to be honest if it was me I'd do as you describe and fit a standard m8 helicoil and a suitable standard m8 set screw.

 

I can only imagine they did it to make tensioning faster/easier but agreed it seems overkill. But then who knows what Peugeot were thinking many times, rear beam strap for example?!

[jackherer 543]

I'm sure you're right but they hate it when they can't supply something and they seem to like a challenge!

Our sales counter (open Monday to Friday) services local industry, as well as members of the public who usually come in looking for that "unusual" or "no longer available" fixing, knowing that we can more than often supply it and, if not, offer a suitable alternative.

 

Remember: "If you can't find it, let Suffolk Fasteners find it for you"

 

I'd forgotten about rear beam straps until last week when I swapped a beam for a mate and had to remove one and explain why we didn't need to keep it.