Calling All Machinists - Valve Cover Gasket Bolt Size (1 Viewer)

[GremlinMobile]

I know there have been a number of threads about this, but this question is more regarding these metric sizes in general..

I took off my valve cover, and one of the bolts was really hard to get out. I got lucky - I backed the bolt out a little bit at a time, sprayed in a penetrant oil, waited, and gave it another crank until it eventually came out, but it could have easily snapped on its way out. So, before putting the cover back on, I wanted to clean out the threads on the bolt and on the receiving end on the engine.

I have a metric tap and die kit. I seem to have found that the bolt is a M6x1.0. The die I have for that size fits the bolt perfectly and I was able to run the die up and down on the bolt to clean it up. It was snug, not too tight, not too loose. Then, when I grabbed the matching M6x1.0 tap, it was super tight to get into the hole on the engine body. I stopped. I tried to insert that tap into another spot on the car that received an M6 bolt just to see if it would fit. It was super tight and wouldn't go in. I then found a random M6 nut in my toolbox that went onto the valve cover bolt perfectly. I took that nut and went to run the tap through it and it was REALLY tight. Using a ratchet, and some oil, and working the tap incrementally, I was able to run the tap all the way through that sacrificial nut, but it definitely cut deeper threads into the nut. The valve cover bolt now goes into that nut, but it's more sloppy.

I purchased a new M6x1.0 tap (made in Japan), and it functions the exact same way - too large. My caliper measures the tap to be larger in diameter than the bolt.

What is going on here? The die fits the bolt, but the matching size tap is too large for the nut? How is this possible? What kind of tap do I need to chase the threads on the engine so that I have an easy time putting the bolt back in? The bolt nearly snapped on its way out so I want to make sure the threads are good before I put it back in.

 

[MountaineerLC]

I don’t have a direct answer for you, but you may need a thread chaser vs a tap. The chaser will clean up the existing threads vs cutting more.

 

[excessive]

i believe the thread pitch on those is m6 x 1.25

 

[GremlinMobile]

No. The thread pitch isn't the problem. I have a thread gauge in my tap and die kit that fits spot-on with the 1.0 pitch. Also, the M6x1.0 die spins perfectly on the bolt. It's the diameter of the bolt and the matching tap that's the issue.

 

[TioCoyote]

Could it be the class of fit, possibly?

The other option would be that the tap is for a different style of bolt. Galvanized bolts, for example, use a larger diameter tap than standard bolts.

 

[suprarx7nut]

i believe the thread pitch on those is m6 x 1.25

That's not a JIS size, so that would surprise me. Anything M6 on a Toyota should be M6x1.0.

Could it be the class of fit, possibly?

The other option would be that the tap is for a different style of bolt. Galvanized bolts, for example, use a larger diameter tap than standard bolts.

Yup. Thread class.

There's the diameter, the pitch and then the class. You can think of class as the descriptor for the "tooth" of the thread. JIS is typically Class 2, it appears. Now, how that compares to the generic M6x1.0 tap you'd get from Craftsman or Husky... I have no idea.

 

[GremlinMobile]

That's not a JIS size, so that would surprise me. Anything M6 on a Toyota should be M6x1.0.



Yup. Thread class.

There's the diameter, the pitch and then the class. You can think of class as the descriptor for the "tooth" of the thread. JIS is typically Class 2, it appears. Now, how that compares to the generic M6x1.0 tap you'd get from Craftsman or Husky... I have no idea.

I guess that's what I was trying to find out - if there's anything else to this other than diameter and thread pitch... I've talked to countless people so far and nobody has any idea why it wouldn't work. I can't even get a straight answer as to why a M6x1.0 tap won't fit into a M6x1.0 die from the same kit!

I was advised to get a thread chaser instead of a tap, idea being that the tap might not catch onto the existing threads readily and might want to cut new ones whereas the chaser is essentially a bolt with a few cleanout slots. My issue with that is the diameter of this alleged 6MM bolt doesn't match the M6 tap, so why would I think that some chinese M6 thread chaser would be any different?

Where the hell do you even get a tap or chaser for this JIS Class 2 M6 bolt hole?

 

[suprarx7nut]

Your tap and die question is easy.

One word: clearance.

The female threads created must be slightly larger than the male threads. They absolutely cannot be the same.

The tap creates the female threads and is larger than the die which creates the male threads. If the tap fit into the die it would be impossible for them to create compatible parts.

The size difference between the tap and die is essentially your thread class.

 

[GremlinMobile]

That explains that, but what explains why a M6x1.0 tap does not fit ANY M6 threads on our cruisers? Let's face it, the steel on these cars isn't known for being the most corrosion resistant. A number of us have sheared off bolt heads on the skid plates and other parts. Re-threading is necessary and it would be helpful to the community if we figured out what tools we can use to deal with broken nuts and bolts and cleaning up threads as these cars become older and more corroded.

 

[TioCoyote]

You can make a thread chaser by cutting longitudinal gullets in a bolt. This gives the junk somewhere to travel. Work it slow and clean it out often

 

[mokrunka]

Sometimes, depending on the condition of the threads, it can be difficult to tap. What I normally do is use a lot of oil, and go in a half turn, back out a 1/4 turn, and just continue working it that way as you go. You have to keep the tap lubed with cutting fluid, and backing out a bit lets you clear chips as you go.

I recommend getting a chunk of aluminum, drilling the tap drill size in it, and practicing to get a feel for, well, how it should feel. You don't want the first time you tap a thread to be on your cylinder head.

 

[Rhetoric]

I would be wanting to use a thread chaser in this instance as you want to just clean the threads.

When I lived in TDI land I would use this 10mm spark plug rethread tool to chase the threads of glow plug holes as they had the same fragility as these valve cover bolts.

 

[89BIGBLUE]

I guess that's what I was trying to find out - if there's anything else to this other than diameter and thread pitch... I've talked to countless people so far and nobody has any idea why it wouldn't work. I can't even get a straight answer as to why a M6x1.0 tap won't fit into a M6x1.0 die from the same kit!

I was advised to get a thread chaser instead of a tap, idea being that the tap might not catch onto the existing threads readily and might want to cut new ones whereas the chaser is essentially a bolt with a few cleanout slots. My issue with that is the diameter of this alleged 6MM bolt doesn't match the M6 tap, so why would I think that some chinese M6 thread chaser would be any different?

Where the hell do you even get a tap or chaser for this JIS Class 2 M6 bolt hole?

You could peek at McMaster Carr.
They might have one.

 

[suprarx7nut]

That explains that, but what explains why a M6x1.0 tap does not fit ANY M6 threads on our cruisers? Let's face it, the steel on these cars isn't known for being the most corrosion resistant. A number of us have sheared off bolt heads on the skid plates and other parts. Re-threading is necessary and it would be helpful to the community if we figured out what tools we can use to deal with broken nuts and bolts and cleaning up threads as these cars become older and more corroded.

Have you tried a JIS M6 tap specifically?

I think the generic taps are going to have a larger tap so that bolts fit easier.

Automotive tolerances, especially Toyota, are tighter than Ace Hardware or Home Depot, haha.

 

[Rednexus]

They are all M6x1.00 and any cheap M6x1.00 bolt/tap should work. My rig is a mixture of real Toyota M6x1.00 and M8x1.25 hardware and M6x1.00/M8x1.25 hardware I buy by the pound at our local farm supply store. They all work together just fine. No issues on the few times I've had to re-tap things as well.

 

[2001LC]

If anyone finds a JIS thread chase kit. Please let me know where. I'd love one.

Some parts store lone out these kits. Oreilly's is one I know has them.

It's not JIS, but works well enough.

 

[GremlinMobile]

They are all M6x1.00 and any cheap M6x1.00 bolt/tap should work. My rig is a mixture of real Toyota M6x1.00 and M8x1.25 hardware and M6x1.00/M8x1.25 hardware I buy by the pound at our local farm supply store. They all work together just fine. No issues on the few times I've had to re-tap things as well.

You're wrong. I think you can prove that to yourself by going to ANY M6 bolt on your car right now, unscrewing it, and running "any cheap M6x1.00" tap through it. Please take a video of you doing it so we can all see. Your tap will be cutting threads HARD to fit into the hole. If you're lucky and your tap doesn't break, you'll cut much deeper threads into the hole and your bolt will go back in just fine but it won't have the same tolerances that Toyota had engineered.

 

[GremlinMobile]

If anyone finds a JIS thread chase kit. Please let me know where. I'd love one.

Some parts store lone out these kits. Oreilly's is one I know has them.

It's not JIS, but works well enough.View attachment 3589059View attachment 3589058View attachment 3589057

I believe the kit you're suggesting might work. Whether it's JIS or not, I don't know. Either way, this whole thing ended up being a moot point. I ran a die on the bolt that was difficult to get out to clean up the threads, oiled it, and it went in just fine. The problem I ran into is that I ended up snapping one bolt on each side of the valve body, so now my valve covers are missing one bolt. Seems like it's an impossible job to drill the studs out so I'll be stuck with this and will hope that it doesn't result in a growing oil leak.

 

[Rednexus]

You're wrong. I think you can prove that to yourself by going to ANY M6 bolt on your car right now, unscrewing it, and running "any cheap M6x1.00" tap through it. Please take a video of you doing it so we can all see. Your tap will be cutting threads HARD to fit into the hole. If you're lucky and your tap doesn't break, you'll cut much deeper threads into the hole and your bolt will go back in just fine but it won't have the same tolerances that Toyota had engineered.

My apologies for offering advice that was taken as offensive and generated such a reaction . Asking for a video of me tapping a bolt is, to be frank, a strange and unusually combative request that I am not going entertain. If you want to see some of my handiwork in turning (at this point) the majority of bolts in my rig, my build thread is linked below.

In all seriousness, seeing that you are located in NY, the bolts were probably hard to tap due to corrosion of at least the bolt and possibly galvanic corrosion of the steel/aluminum interface (which also weakened your bolts, made them hard to turn, and caused them to break off). It's going to be hard to tap because the I.D. of the hole is smaller than it was from the factory due to the buildup of corrosion that's clogging things up. Your die would have fit the bolt as the O.D. of the bolt would have been smaller due to some of it being left in the hole as corrosion. The tap is designed to clean out all of that gunk.

If you're too afraid to tap the hole, your other option would be to over-drill the hole and installing a helicoil (which, being steel-on-steel, shouldn't have the galvanic corrosion issue of the steel-to-aluminum the OEM bolt had). Otherwise, just go slow and clean it out.

 

[GremlinMobile]

My apologies for offering advice that was taken as offensive and generated such a reaction . Asking for a video of me tapping a bolt is, to be frank, a strange and unusually combative request that I am not going entertain. If you want to see some of my handiwork in turning (at this point) the majority of bolts in my rig, my build thread is linked below.

In all seriousness, seeing that you are located in NY, the bolts were probably hard to tap due to corrosion of at least the bolt and possibly galvanic corrosion of the steel/aluminum interface (which also weakened your bolts, made them hard to turn, and caused them to break off). It's going to be hard to tap because the I.D. of the hole is smaller than it was from the factory due to the buildup of corrosion that's clogging things up. Your die would have fit the bolt as the O.D. of the bolt would have been smaller due to some of it being left in the hole as corrosion. The tap is designed to clean out all of that gunk.

If you're too afraid to tap the hole, your other option would be to over-drill the hole and installing a helicoil (which, being steel-on-steel, shouldn't have the galvanic corrosion issue of the steel-to-aluminum the OEM bolt had). Otherwise, just go slow and clean it out.

You sound just like my wife! JK. Your advice wasn't offensive at all. Your theory about part of the bolt's threads being left in the aluminum, making the aluminum hole harder to tap is a fair theory, but it is just a theory. This issue exists with every M6 bolt/nut on this rig, steel/aluminum and steel/steel interfaces. A lot of the bolts are perfectly easy to get out, but the tap still doesn't fit the holes.

I'm just saying before you invalidate what I'm saying I'm seeing, and before you discredit everyone on this thread whom theorized that the treads are JIS class, try it out for yourself. Don't take a video if you don't want want