MTFCA Forum

Hello,

if i want to change the mainbolts from squarehead to hexhead which bolts have i to use?

8.8 / 10.9 ?

Cant find a boltkit at Langs / Snyders or Macs.

Thanks

Michael

Modern bolts aren’t usually straight enough to make good main bolts. I haven’t seen any of the new bolts from the vendors for several years, but they sometimes didn’t fit very well either. Try to find some good originals if you can. I would think Langs or someone might have good originals.

I have done it numerous times. I do buy Grade 8 fine thread bolts. The fit has always been totally acceptable. I torque them to 60 ft lbs in three stages. For the rear two I grind a suitable flat on the heads.
I first did this in the ‘70’s on a A cranked pressure oiled engine that is still running strong to this day!!

I do the same as Les has described! I add stover style locking nuts as well.

Hank

For years and years it was possible to purchase high quality hex head bolts with very straight shanks that worked well for replacement man bearing bolts. Along with new technology came the change to the heat treat process where longer bolts were no longer loaded into baskets and kept vertical when quenched and tempered but rather run thru furnaces on conveyor belts laying flat. After years of spending hours at my fastener distributor sorting cases of bolts to find the ones with reasonably straight shanks and lastly resorting to sorting and then straightening bolts, I gave up and started having main bolts custom made with centerless ground shanks as a last resort. So with that said be very carefull in selecting and using new bolts as its common to find them with up to 1/16" bow or more . For a stock engine, I don't understand why originals are not good enough. They are well-made and plenty out there. Get a 9/16" 8 point socket for the square end and you are all set.

Michael
In Germany I suppose you can only buy Metric size bolts. 12 mm I suspect are marginally close enough fit (but perhaps they do fit nicely (obviously I don’t have any experience with them)). In Canada while we are “officially” metric, Imperial sizes are very available!! So perhaps the best of both worlds!!
Metric “conversion” occurred in the ‘70’s here, but many things have never changed except perhaps in the description!!
So if the 12 mm bolts don’t fit nicely, then perhaps 14 mm bolts and consider getting them ground or perhaps consider reaming the holes. Assuming that a 14 mm reamer is reasonably available.
Just some thoughts!
All the best.

Hi to all,

thanks a lot. I will have a look at the "Screw-Shop" - after the Lockdown in Germany

The problem is not that i find the original bolts are bad. Here in germany the socket for the square head is not available and it is difficult to do the job.

Stay healthy - thanks for your help

Michael

Ford wrench 5Z-156 is a tool made for the square head crankshaft bearing bolts. They are plentiful and inexpensive.

For giggles, i checked ebay. Look for double square 9/16 socket. Many available cheep.

9/16”. 8 point socket is all you need. 1/2” drive is best. Dan

Here is a 9/16 8 point socket on E-bay Germany- 7 Euros!

https://www.ebay.de/itm/363378958675?ha ... SwEbxgjCDo