engine bolts - high tensile?

[slimtim]

My dad went to get some M12 ss bolts to mount my 70hp tohatsu 2 stroke today and was told that we should be getting high tensile bolts...is this really necessary considering that you're bolting around a nice soft aluminium engine saddle?

Cheers

Tim

[Pete7]

Tim, might be wrong but I think they are 1/2" UNF. A lot of shock loading on those 4 bolts when you are bouncing through the waves btw.

Pete

[Richard B]

Yes, high tensile, as most steel bolts are (it's a property of steel don't you know! ) and UNF threads - I guess that will be less likely to shake loose than a coarser metric thread. I'll try and dig out the address where we got ours from of that helps.

[Richard B]

It was these people - they may not necessarily be the cheapest but they have huge stocks and fast delivery http://www.namrick.co.uk

[slimtim]

Tohatsu manual states M12 105mm long (100mm would be ok though). Kevin Mole outboards just told me it would cost me 100 quid for 4 bolts !!!!!!!!!

Richard, thanks for the link, I'll check them out. Surely I should be able to get them for less than 25 quid a pop?

Tim

[Pete7]

Originally Posted by slimtim

Tohatsu manual states M12 105mm long (100mm would be ok though). Kevin Mole outboards just told me it would cost me 100 quid for 4 bolts !!!!!!!!!

Tim

thats cheap then, well the alternative for 1/2" UNF is the scrap yard barge with boxes of suitable bolts. Stick a 12mm drill in one of the unused holes and see what size it is. Suzuki used to have a very course pitch btw.

Pete

[Mark Halliday]

Tricky one this Tim

HT bolts (marked with 88 on the head) are great in tension, but not so good in shear.
What you have to do is work out what sort of loading you are putting on them.
My 140 is stuck on with 1/2" UNF s/s and it aint going nowhere.
If you are worried about metric coming undone, use Ny-loks.

CP Fastenings in Southsea are a good supplier. 023 92 73 07 21

[slimtim]

Ok, I don't care whether I use M12 or unf bolts. The tohatsu manual says M12, but if unf will be cheaper/better then I'll go for those!

I had a look on the site richard posted but there doesn't seem to be high tensile stainless bolts listed...unless I'm looking in the wrong place?

So what do I need? if Mark's 140 is bolted on with 1/2" unf ss bolts then surely that would be ok for me? Are they high tensile mark?

The bloke at kevin mole said that if you don't use high tensile bolts, the threads can go.

I'm more confused than I was before

Thanks for the advice.

Tim

[PeterR]

Slimtim,I god damn sure you dont need to spend 100 quid on four bolts

[PeterR]

P.S Dont forget your engine bolt lock for your insurance conditions