bolt sizes (1 Viewer)

[Heartworm]

I don't have good measuring equipment so I thought I would seek advice from those who have the experience. Our 1987 FJ60 has the skid plate for the transmission/TC. Unfortunately, it is not on the vehicle. The PO said that there was a flood and he removed it to clean up the mud that accumulated. In the process, he twisted off all five (5!) bolts!
I have drilled one of the bolts through but with a drill that is smaller in diameter than the bolt. I removed a bolt from the skid plate from my 1986 FJ60 and it measures 1.25X8M according to the cheesy tap and die set that I have. The bolt will thread perfectly into the 1.25X8M die that I have, but the 1.25X8M tap makes a hole that is way too big. I am suspecting that the tap is mislabeled.
So, am I alone in this particular problem or have others dealt with this mess? Do I just drill out to a bigger size? What would you recommend...a 10mm bolt? Or, some US size bolt?

 

[grant5127]

Seems your tap is bogus..... you could get another or I have gone the 10mm route myself... I prefer to stay with metric tho....

 

[GulfShoresFJ60]

Does the tap fit in the die? If not then I agree with grant5127 that your tap is messed up.

 

[Elbert]

run down to lowes if you have one in your area with your known good bolt. they have a size chart near the bolt area where the grad 5 * 8 stuff is. screw your bolt into the right nut and the size is listed. I have an 86 FJ60 I assume the 87 is the same. I would look at mine except its raining which is a good thing here in the South.

I belive it may be time to drill out to the next avalaible size grade 8 bolt..... Since I've neve had my skid plate off (will soon) I don't know if the nuts are welded on the frame or what. You'll have to take that into consideration at to your plan of attack.

 

[2mbb]

The bolts that hold that skid plate on have the part number: 91661-60820

The first five digits must specify the style (bolt head style, washer, lock washer, etc. I don't have info on this, but I know the bolts have a fender-style washer and maybe a split lock washer.

The second five digits specify the bolt class and size. The first digit "6" is the class--I think this is related to the bolt grade. Toyota grades bolts either 4t, 5t, 6t or 7t. "6" is the 6t grade. the next two digits ,"08" are the diameter in mm--this is an 8mm bolt. The last digits "20" are the lenth in mm. The pitch is 1.25mm.

I got this information on bolt sizing from a section in the back of the 2f engine manual.

 

[Heartworm]

Thanks to all. I agree with the comments that my tap is mis-labeled. What would one expect from a "complete" set that cost about $15??? Duh! You get what you pay for. I am leaning toward going to a bigger bolt. I think that there are nuts welded to the inside of the frame rail and that they are large enough to handle a bigger size hole. Will post my results.

 

[2mbb]

Why not get an 8mm tap, drill the bolts out with the drill size indicated on the tap and re-thread the frame nuts? Why do you have to go to a larger bolt size? If the bolt is not holding properly after re-threading to 8mm, install an 8x1.25mm helical coil thread repair. I think this would be a better approach over trying to fit a 10mm bolt into an 8mm nut.

 

[Heartworm]

I hear you about the 8mm. My problem is that I am rarely good enough to drill the bolt out exactly in the center. I use a starter punch, but it seems that the drill often goes in a little excentric. Thus, when the bolt remnants come out, the original hole is hogged out on one side. I probably will buy both sizes and go for 8mm first and if I screw up, then go larger.

 

[2mbb]

You might find that when you drill the nut using the appropriate drill size for an 8mm tap that the drill will self center in the hole of the nut.

 

[Heartworm]

Update & Report

The drilling out of wrung-off skid plate bolts is a sucky job from hell. Anyone who does not use some anti-seize when they put their bolts back should be banned from cruiserland. I was able to drill the broken bolts out by the following procedure: 1. used a starter punch to try to make a centering mark (never really centered exactly). 2. started with a DeWalt 3/8" pilot point bit because the hole in the frame helped center the bit in the broken bolt while I drilled a starter crater in the center of the hole. 3. Switched to a 1/4 inch size (or less) disposable bit to drill out the bolt. 4. Here is the "special secret": Use a floor jack to support the drill and to put gradual pressure on the bit (as told to me by Jim C..he da man!) 5. Final drilling with a 17/64 bit to accommodate the tap 6. Tap threads with a 8X1.25 tap. 7. Used oil in all steps to help the bits.

Tomorrow I will see if it all will really work. Going to change the oil in the trans and TC before I put the skid plate back on.