Correct bolts/screws to attach trans adapter plate to GM Engine

Joel K

Supporter
My kit came with Buttonhead 3/8” 16pitch x 1.25. Button head bolts which thread into my LT4 engine block. All the pics I see is that these screws are cap head and not button head. I tend to like cap head screws better since the sockets tend to be deeper than the button head, My question is, should these bolts be standard stainless 18-8 stainless screws or some other type of screw.

Thanks for the help.
 
I wouldn’t use stainless for anything other than non structural bolts. I’d also argue that anything bigger than 1/4” should be grade 8 or better.
 
Let's not go through this again. :confused:

Lol then offer your opinion and leave, Joel can make up his own mind. But please some recommend that he use worthier aerospace grade fasteners (on the cheap) or titanium for this particular location.
 

Joel K

Supporter
Let's not go through this again. :confused:

LOL I guess I hit a nerve.

Here is a pic of the cap heads marked with green from Cam’s car...
DC134B88-A250-4805-AA44-3CE7A0C7296C.jpeg


To me because they are shiny they appear to be stainless.

Here is a pic of what I think was included in my kit for this purpose and they do not have markings other than the manufacturer.
55F48D9F-6AF3-4CB3-9F16-3936F5DC7F3E.jpeg


As stated above, I would prefer to use cap heads and there are a number of choices, steel, plated steel, very expensive hardened stainless cap heads, and standard 8-18 stainless so just looking to get some guidance.

I’m just fitting my engine in for the first time to get a sense for what chassis mods I may need to make to accomdate the front facing
 

PeteB

GT40s Supporter
I used alloy steel capheads for this. I'm with Cam, I wouldn't use stainless. However, titanium would be total overkill.
 
Joel - I used grade 8 alloy steel or grade 10, whichever I had available at the time (I don’t recall which right now). I prefer using cap head bolts as well for the better engagement but used button head for aesthetic or clearance reasons.

Neil and I have a history debating appropriate use of fasteners, I forget what thread it’s in now. No need to muddy this thread up.

If you have questions about the appropriate use of fasteners I recommend you find someone you trust to help you or use the general rule I mentioned above - stainless for non structural locations, anything bigger than 1/4” and go with alloy steel. That’ll serve you well for just about everything you’re going to do on a street driven car.
 

Joel K

Supporter
Joel - I used grade 8 alloy steel or grade 10, whichever I had available at the time (I don’t recall which right now). I prefer using cap head bolts as well for the better engagement but used button head for aesthetic or clearance reasons.

Neil and I have a history debating appropriate use of fasteners, I forget what thread it’s in now. No need to muddy this thread up.

If you have questions about the appropriate use of fasteners I recommend you find someone you trust to help you or use the general rule I mentioned above - stainless for non structural locations, anything bigger than 1/4” and go with alloy steel. That’ll serve you well for just about everything you’re going to do on a street driven car.

Yes, I do remember that thread and appreciate everyone’s opinion. There can always be multiple correct answers.
 

Joel K

Supporter
This won’t be accessible and you’re going to want to set it and forget it. Go with zinc plated for corrosion protection. The black oxide doesn’t hold up well when it comes to corrosion.

Got it, thanks Cam this makes sense and is simple. I am definitely not going to track this car so your suggestions definitely help. Just asking questions like these to avoid mistakes that will cause me to re-do stuff later in the build.
 

Neil

Supporter
Most socket-head cap screws (bolts) are black oxide finished because it is more expensive to plate a high alloy bolt and then bake out the hydrogen to prevent hydrogen embrittlement. The hydrogen gas that is produced when a part is plated makes a high alloy (high strength) part prone fracture unless the hydrogen is baked out of the steel. Black oxide does not produce hydrogen.

Titanium is nice but most 6Al4V titanium aerospace bolts are fine thread; threaded holes in most blocks are coarse thread.
Be sure to lubricate the threads- anti-sieze is mostly foolproof.
 

Ken Roberts

Supporter
Button head bolts are just plain wrong (most likely the head would not even fit in the counter bored hole in the adapter). They are not intended for high strength fastening due to the shape or the head (weak). Your fasteners into the block should be m10x1.5x45 I believe. They are automatically a 12.9 fastener.

Did you even try to thread those standard bolts into the block? They should be metric on a LT4 block. Make a list of the incorrect fasteners that have been supplied. That way Fran can supply you with the correct ones you have paid for in the completion kit.

Here are the ones I ordered for my LS9 block. https://www.mcmaster.com/91502a228

As a side note ARP bolts can be purchased in alloy or stainless at the same tensile strength. I guess the key note is the correct grade of stainless. Depends also if the threads are rolled verses cut. Personally I would stay with alloy.
 
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Joel K

Supporter
Button head bolts are just plain wrong (most likely the head would not even fit in the counter bored hole in the adapter). They are not intended for high strength fastening due to the shape or the head (weak). Your fasteners into the block should be m10x1.5x45 I believe. They are automatically a 12.9 fastener.

Did you even try to thread those standard bolts into the block? They should be metric on a LT4 block. Make a list of the incorrect fasteners that have been supplied. That way Fran can supply you with the correct ones you have paid for in the completion kit.

Here are the ones I ordered for my LS9 block. https://www.mcmaster.com/91502a228

As a side note ARP bolts can be purchased in alloy or stainless at the same tensile strength. I guess the key note is the correct grade of stainless. Depends also if the threads are rolled verses cut. Personally I would stay with alloy.

Thanks Ken, as you suspect I just may not have the correct bolts yet from Fran since the completion kit is back ordered. I did receive a box of bolts for the transaxle and these seem like the only bolts that would be appropriate. They do clear the counter bored holes and do screw into the block although not very deep. They are labeled as well in the package as 3/8 16 1-1/4.

I’ll shoot a note to Kristin and see what she says.
 

Joel K

Supporter
Thanks Ken, as you suspect I just may not have the correct bolts yet from Fran since the completion kit is back ordered. I did receive a box of bolts for the transaxle and these seem like the only bolts that would be appropriate. They do clear the counter bored holes and do screw into the block although not very deep. They are labeled as well in the package as 3/8 16 1-1/4.

I’ll shoot a note to Kristin and see what she says.

Ken, now that I am looking more closely at the printouts that came in the box of bolts I definitely confused myself, those 3/8” bolts are for the door hinges. They included 8 M8x25 to connect the transaxle to the plate but no bolts were included to attach the trans plate to the engine.

I just ordered the bolts you used. I measured the depth of the threads in the block and they appear to be perfect length.

Thanks again Ken!
 
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If thats an LS block i think youll find the bell housing to block bolts are 10 x 1.25, and no i wouldnt use stainless either, i use plated grade 8 cap screws in a very similar housing.
 

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Ditto what Neil said.

Hopefully you found some Grade 8 equivalent type cap head bolts, with a finish other than black oxide. The yellow zinc holds up well. McMaster tends to have a pretty good selection including finishes other than just black oxide. I wouldn't buy bolts off of ebay....who knows what country of origin they came from and what quality controls (or not) were in place. Buy from a reputable source like McMaster and sleep better.
 

Joel K

Supporter
Ditto what Neil said.

Hopefully you found some Grade 8 equivalent type cap head bolts, with a finish other than black oxide. The yellow zinc holds up well. McMaster tends to have a pretty good selection including finishes other than just black oxide. I wouldn't buy bolts off of ebay....who knows what country of origin they came from and what quality controls (or not) were in place. Buy from a reputable source like McMaster and sleep better.

Agreed, I buy most of my bolts from McMasterCar, I’m lucky since they are located 7 miles from my house.
 
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