Need a specific machine screw - does it matter?

[JHZR2]

This is auto repair but it’s more general.

I’m trying to reseal a diesel injection pump. One of the T30 screws was messed up and stripped. My attempt only made it worse.

A rocket socket made short work of the removal. The cover is keeping oil in this:

I also removed the back plate to seal that. Also T30. Of course the two screw types are different.

I need the one on the right. The threads on both screws are the same. But the one on the right has that little flat top. Why?

The screw barely appears from the top…

I can apply torque to the buggered threads for loosening and tightening. They were just too hard in there after 32 years.

Is this a special variety of screw? I’ve seen them before but don’t know their name.

Do I dare use it again with some antiseize and some more on the hole on the top? I can’t imagine that I should be tightening any of these very much. I have no spec.

Thoughts?

Thanks!

 

[SC Maintenance]

If your referring to the little tapered protrusion at the bottom of the threads, its there to make it easier to get the bolt started and make it harder to accidentally cross thread. As long as the threads are the same and the head size is such that it doesn't interfere with anything else, it shouldn't matter. Just make sure you don't get it started cross threaded.

 

[Nukeman7]

You should be able to source a replacement fastener at a good hardware store. The style of screw is called a T-30 Torx socket head capscrew. Try screwing the original screw back into the body of the pump without the cover plate or gasket to see if the threads can protrude through the back opening of the pump. If so, the flat shoulder serves no critical purpose. If you have problems locating the T-30 capscrew in the correct metric size, you can substitute a metric socket head hex capscrew that uses an Allen wrench in lieu of the Torx bit.

 

[eljefino]

The only concern I would have with a substitute fastener is getting a similar metallurgy and plating. Yours looks cadmium plated. Not knowing what it's going into, I would say avoid stainless due to galling and mild steel due to not being particularliy corrosion resistant. If it were up to me I'd take the existing one and cut a slit in it so I can drive it in with a flat head screwdriver, or find one in my junk drawer that's from a car, preferably a Mercedes, so it matches the others in quality. I've had a lot of auto parts store/ hardware store fasteners that corrode quickly or take a slightly different size driver.

Both the threadless upper and the torx drive are innovations engineered for faster, more robotic assembly. The Torx bit stays put in its driver better at the factory.

 

[vavavroom]

That's a locating screw for easier installation.

 

[doitmyself]

It appears to be metric hardness 8.8 (not 5.8, 10.9 or 12.9.)

 

[spasm3]

My local home Depot has cap screws in stock. I would think steel with antiseize should work. Eyeballing it it looks like an m8 x 1.25

I recently bought a thread checker to have in my garage, so I know the size to order online if I have to.

 

[andyd]

Another vote to slot and re-use

 

[CleanSump]

The only concern I would have with a substitute fastener is getting a similar metallurgy and plating. Yours looks cadmium plated.

Coating is irrelevant. It's holding a stamped sheet steel cover plate on an aluminum mechanical injector pump housing.
Not like going into a titanium BMW transmission or titanium Mercedes engine block. Carbon steel or stainless is fine.
Cadmium plating is going the way of mercury due to environmental rules making it a problem for manufacturers. Google persistent pollutants and manufacturing.

 

[MSCH]

This is auto repair but it’s more general.

I’m trying to reseal a diesel injection pump. One of the T30 screws was messed up and stripped. My attempt only made it worse.


View attachment 153402

A rocket socket made short work of the removal. The cover is keeping oil in this:

View attachment 153403

I also removed the back plate to seal that. Also T30. Of course the two screw types are different.

View attachment 153404

I need the one on the right. The threads on both screws are the same. But the one on the right has that little flat top. Why?

The screw barely appears from the top…

View attachment 153405

I can apply torque to the buggered threads for loosening and tightening. They were just too hard in there after 32 years.

Is this a special variety of screw? I’ve seen them before but don’t know their name.

Do I dare use it again with some antiseize and some more on the hole on the top? I can’t imagine that I should be tightening any of these very much. I have no spec.

Thoughts?

Thanks!

if the threaded fastener is not proprietary in nature or has a high yield specialty markings and has standard SAE or SIO threads, you can use whatever fits.

 

[CleanSump]

if the threaded fastener is not proprietary in nature or has a high yield specialty markings and has standard SAE or SIO threads, you can use whatever fits.

Yep Sir. I've had three MBs with mechanical injection pumps. It just hold an access cover on. They are usually only removed to replace the gaskets. The screws are nothing special, just good quality and torx drive.

 

[JHZR2]

Another vote to slot and re-use

Well, I dont even think I need to slot it. I can drive it with the Torx bit, and can even remove it when there’s no galvanic funny business.

The rocket socket did minimal damage, and it’s upside down where nobody will see it anyway. If it weren’t for this one fastener, I probably would have done the gasket from underneath, upside down. There is some acrobatics involved but it’s a lot less work than pulling the IP.

Now the question is, since there’s no torque spec, and it’s essentially an o ring going in there, how much do I torque it???? Less is obviously better on the bad fastener for install and especially removal…

 

[mk378]

Stamped metal covers will deform and leak if overtorqued so you're right the torque should be low. This is a really non-critical application and any cap screw with the correct thread pitch (looks like M6 x 1.0) and threaded length will work. They should be reasonably available with hex key heads.

 

[spasm3]

Now the question is, since there’s no torque spec, and it’s essentially an o ring going in there, how much do I torque it???? Less is obviously better on the bad fastener for install and especially removal…

How much pressure does the pump produce?

 

[JHZR2]

How much pressure does the pump produce?

This gasket holds no pressure. Just the splash lubrication of the injection pump. It makes its way in through a bore in the block, and drains back out by gravity. Nothing fancy.

 

[spasm3]

This gasket holds no pressure. Just the splash lubrication of the injection pump. It makes its way in through a bore in the block, and drains back out by gravity. Nothing fancy.

I don't know what know nd of gasket, but it sounds like good and snug. Maybe if you wanted to make sure it's even, 3.3 ft/lbs, as I look at an m6 chart.
If it's m8 maybe 8lbs.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.fastenermart.com/files/metric_tighten_torques.pdf&ved=2ahUKEwjoxKu25NL-AhVckWoFHVHfDF8QFnoECCQQAQ&usg=AOvVaw2cP2K5Y1Kq0i4rYLZknaJ2

 

[64bawagon]

If its only marked 8.8 then almost any screw of similar thread and pitch will work, chose whatever your hardware store has that looks right, 8.8 is nothing special. Plating has really gone downhill in recent years, its not nearly as robust as in the old days. Anything plated will suffice, likely a simple zinc plating is what your store will have.
Like others have said the point is for guiding the screw into the threads, its a called a "dog" or "extended" point.

 

[Chris142]

You are overthinking this. Put in the slightly different bolt and forget about it.

 

[Astro14]

@JHZR2 you can get very close to the original screw here:

Torx Socket Low Head 8.8 Zinc M6X1.0 Coarse ISO 14580

Bel-Metric sells metric hardware & specialty automotive supplies nationwide. Visit our website to purchase metric fasteners, nuts, bolts, Time-Sert kits & more.

belmetric.com

If the threads in the casting are buggered, helicoil will provide plenty of strength. There’s enough meat in the casting to allow for the helicoil.

One other point - this fastener had a large head - this helps spread the clamping force over a large area to prevent distorting the cover.

Whatever you put on there - use a washer of the same size as the head to spread the load.

 

[Skippy722]

Well, I dont even think I need to slot it. I can drive it with the Torx bit, and can even remove it when there’s no galvanic funny business.

The rocket socket did minimal damage, and it’s upside down where nobody will see it anyway. If it weren’t for this one fastener, I probably would have done the gasket from underneath, upside down. There is some acrobatics involved but it’s a lot less work than pulling the IP.

Now the question is, since there’s no torque spec, and it’s essentially an o ring going in there, how much do I torque it???? Less is obviously better on the bad fastener for install and especially removal…

I’d go with a mild “gggrrr” with a hand tool, not too tight but enough that it shouldn’t work loose. Maybe like…. 10ft lbs at most, should be perfectly adequate.

I would use a new screw though. Doesn’t need to match exactly, just thread length and pitch.