Anyone know right off the top of their head what the correct OEM bolt strength was/is for the bellhousing mounting bolts. (75 280Z , 4 speed manual) Got a couple on the bottom that look kind of rough so I thought I'd look around for suitable replacements. I know what size and thread pitch they are, (10mm x 1.5 x 60mm) just need the strength rating...

webdawg1

I wouldn't think it matters much in this position. Any quality bolt should do in my opinion. If anyone knows different please chime in.

Are you sure they are 1.5 pitch? I only ask because nearly all the 10mm bolts that I have encountered on the car are 1.25 pitch, same for the 12mm bolts.

These bolts will be exposed to the elements, so they either need to be stainless steel or plated/coated, eitherwise they will rust right up. Might as well buy Grade 8 bolts as well (which is the typical grade for automotive fasteners on our Zs).

Yeah, I'm sure.... Believe it or not, I carry both SAE/Metric thread gages on my key chain and my trusty 4-way Sears pocket screwdriver. When I'm at the house and working out in the garage I also use a bolt size gage I got from www.fastenal.com as well as the metric thread gage to verify the thread pitch and bolt/screw size.

webdawg1

Grade 8 your best bet. Stainless depending on type can be too soft.

I concur. They are 10 mm x 1.5 x 60 mm in length. 65 mm long will also work if that's your closest choice. The most commonly found generic bolts are either 50 mm long (too short) or 75 mm which is too long and will bottom out before they get tight.

Anyone have a good tech article on the OEM head bolt markings that were used when these cars were first put together? Or is there such an animal??? On one of the Bellhousing Bolts the head marking looks like 1 9. Or it could be 6 1 if you rotate it 180 degrees, but then the 1 does not look right...if you know what I mean....

webdawg1

I'd also like to know what the numbers on the OEM bolts refer to, as they don't appear to be your standard bolt grade markings. Could they simply be numbered in order to assist the person assembling the components?

I haven't looked at any of mine lately. This has today's standards:

http://www.boltdepot.com/fastener-information/Bolt-Grade-Chart.aspx

I'm famlilar with the "standards", but the numbering on the stock bolts do not appear to have anything to do with these.

I just went out and checked, it looks like I re-used the factory bolts. If I remember I couldn't find bolts the right length.

Just a guess, but the "1 .9" marking could easily be a slightly worn "10.9", which is a metric strength class. (Equal to ANSI grade 8)

If I was going with after-market bolts I would use that grade. But is there a clearance problem with the head... I just don't remember.

That would be kind of interesting to find out.... I've seen various markings on the bolts...mostly 4, 7 , and 9 1. And then some of them have no markings at all...From what I've found so far it appears to be standards related (JIS) Kind of like our SAE...but nothing about the bolt head markings...

webdawg1