Do you know of any models that use M8x1.0 valve adjustment screws?

[rcx132]

I have an aluminium valve rocker with damaged adjustment screw thread. It's an M7x1.0 thread, so I thought no problem, tap this out to M8x1.0 (same pitch so should work nicely) and fit some VW T1 / Beetle screws. That almost worked, the VW screws are the correct diameter and pitch but are 2 mm too short :/

Does anyone know of other cars that use M8x1 tappet screws?

 

[AVI_8]

An air cooled 911 has an 8mm x 1mm thread pitch, think they’re 30mm but they have a swivelling elephants foot which sits on the valve, not sure if that would be a problem with your application
Obviously though there’s a hefty price tag to go with the part though as with all things Porsche

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[hotponyshoes]

Could you not just helicoil it?

 

[addjunkie]

Just use a socket cap screw thats lon* enough and the right thread, cut the head off……jobsa goodun

 

[Ubique]

Or hard face 2mm onto the end of the screw?

 

[rcx132]

Just use a socket cap screw thats lon* enough and the right thread, cut the head off……jobsa goodun

It needs to be hardened (I only realised this from another post).

 

[addjunkie]

Id think 12.9 grade would be fine

M8 x 1mm x 80mm Fine Pitch Socket Cap Head Screws (DIN 912) - High Tensile Steel 12.9 Self Colour

M8 x 1mm x 80mm Fine Pitch Socket Cap Head Screws (DIN 912) - 12.9 High Tensile SteelSocket Cap Heads are a widely used machine screw, which feature

www.gwr-fasteners.co.uk

 

[PhillipM]

I think the Peugeot TU engines are M8x1

 

[Beeezer]

I think the Peugeot TU engines are M8x1

No they don’t.

 

[PhillipM]

Apologies, just checked my box of titanium shiny race bits, they're M10x1

 

[frank horton]

new rocker time....pain to fit tho......

 

[Agroshield]

...2 mm too short

Are they too short at the top or too short at the bottom?

There is a point to what seems a facile question: is it possible to alter (lower) the end that is not too short to gain the extra 2mm at the end that is too short?

Possibly face off the top of the rocker arm where the lock nut bears and thin out the locking nut a little.

 

[mike os]

Thread repair insert ... timesert by choice

 

[Agroshield]

Thread repair insert ... timesert by choice

The problem is that he has already removed the correct M7 x 1 thread and replaced it with an M8 x 1.

This place says an M7 x 1 STI tapping drill is 7.2 (https://www.thorintl.com/Drill-Sizes-HeliCoils-Metric.shtml) so it might be OK.

Is there such a thing as oversize thread repair inserts just in case it is not OK?

 

[hotponyshoes]

Is there such a thing as oversize thread repair inserts just in case it is not OK?

Yes.
You can get oversize inserts.
If it's really bad you can use one insert inside another

 

[hotponyshoes]

Also,
Depending on what caused the damaged thread in the first place, you might just want to fit inserts to all of them while it's apart

 

[rcx132]

Also,
Depending on what caused the damaged thread in the first place, you might just want to fit inserts to all of them while it's apart

So the rockers were new, and original, albeit they were Suzuki-Maruti, which is basically made under partnership in India. I tightened the rockers to factory torque and one of the threads stripped. I checked the other rockers and all of them had slightly loose threads, not big enough to fit an M8 screw, but too big for the M7 they should take. Unfortunately I couldn't return them as they'd sat around for a bit over the chargeback period. So all the rockers should be fixed. The engine itself is low value, I'm only fixing it for personal interest, so I'm not willing to buy rockers from the dealership.

As @Agroshield says, I could mill down the rockers a bit to take the VW screws. I could also put the nut under the rocker (that's worked for now), again using the VW screws. Helicoil... not sure that would work as the screw goes all the way through? I haven't used inserts before but they look interesting.

 

[hotponyshoes]

You can use the inserts on through-holes with no problems
There is a bit that you use to wond them I with but that's designed to be knocked off and.leave the thread clean

 

[Agroshield]

If it's really bad you can use one insert inside another

Is that a recognised and documented manufacturer procedure?

At first glance it sounds dodgy: the inside of the bigger insert will be its nominal thread size (e.g. M8 x 1). The outside of the smaller insert will be the STI thread size for its internal thread size. AFAIK, STI thread dimensions are not the same as ISO metric dimensions. If it were so, you would not have to buy a special STI tap - you could just use the first or second next size bigger same pitch tap.

 

[rcx132]

I've looked at the Timesert inserts. The thread on the outside of the insert is the same pitch as the thread on the inside. So presumably I can still fit them on the rockers I've tapped to a larger size.

The Timesert website is down so I can't find the correct tap size for an M7x1.0 hole.