engine bolts - high tensile?

slimtim · 17 August 2005, 22:09

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 · 17 August 2005, 22:49

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 · 17 August 2005, 23:34

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 · 17 August 2005, 23:36

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 · 18 August 2005, 14:31

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 · 18 August 2005, 15:20

Quote:

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 · 18 August 2005, 15:42

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 · 18 August 2005, 17:30

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 · 18 August 2005, 19:46

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

PeterR · 18 August 2005, 19:48

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

Nasher · 18 August 2005, 20:41

Tim

Went through exactly this a few months back when mounting my Suzi 200.

Having ''been there done that' with Stainless steel bolts shearing off on Motorcycle brakes, I used M12 High Tensile (88) bolts and nylocks to mount the engine and covered them in grease to keep the salt out.

I was quoted about 140quid for the 6 suzuki nuts and bolts which I was NEVER going to pay.

Nasher.

slimtim · 18 August 2005, 21:28

So it seems for me to get high tensile bolts that are STAINLESS will cost me an arm and a leg...or will they be cheaper direct from a bolt supplier somewhere?

If not it seems my choice is either:

1) go for high tensile non stainless and hope they don't rust
2) go for stainless bolts but non high tensile and hope they don't break

I'm not to keen on paying £100 for 4 bolts!

Hightower · 18 August 2005, 21:54

Don't go for rustable steel bolts long term, Tim. Go for the high tensile stainless ones.

Phone Lee Fairweather and ask him, or closer to home phone Kevin Mole....Helped me when I had questions about Hyd Steering.

Andy

slimtim · 18 August 2005, 22:04

Andy,

Kevin mole was the one who quoted me £100 for 4 bolts...apparently stainless steel high tensile. I would imagine they would be yamaha ones (or similar) so I'm sure I could get them a lot cheaper elsewhere. Apparently bolts are normally supplied with a new engine.

Will it really be that risky using ss bolts which aren't high tensile? I would have thought the cast ali saddle of my outboard would crack before a NON-high tensile 12mm stainless steel bolt sheared?

Tim

Richard B · 18 August 2005, 22:09

Quote:

Originally Posted by jwalker

Stainless bolts are not the material of choice, use high tensile ones. Seal them and they'll last for years. They should have 8.8 marked on their heads. They're cheap too. You could use stainless nuts if you prefer. M12's will be fine. Now you just need to find the chunky washers.

I followed this advice back in January 2004, except that I went for UNF. All OK so far, although the bolt heads are discoloured, of course. The biggest problem I had was geting bolts long enough and with thread far enough down the shank, which is why I purchased them from Namrick.

Hightower · 18 August 2005, 22:24

I'll have a rummage though the stores at work tomorrow Tim, don't think we use 8.8 ht bolts any more but use the 12.9 ones instead (Mark Halliday will tell you if these are any good). Will also find out from the designers what tensile strength stainless bolts come in (if you can get em). Thing is the tensile strength of a bolt is mainly dictated by the carbon content of steel.....

Here's another more web site for you to visit: http://www.a2a4.co.uk/

Till tomorrow.

slimtim · 18 August 2005, 22:33

ah ok Richard, understanding a little more now. Thanks for the advice. I have found plenty of suppliers of zinc coated and galvanised ht bolts.

Andy, thanks, that would be great. That website doesn't seem to work!

Tim

Hightower · 18 August 2005, 22:35

Just clicked it, works for me!

nugent · 19 August 2005, 05:53

for what it matters i use this company in birmingham
monofix 0121 359 2117
they supply any bolt you can name and will send via post , my old engine (135hp opti)was bolted on using stainless shear bolts for security reasons sure i paid £8.00 per bolt including nyloc to go over the shear head after wards to be safe like.even though i used threadlock 243 on it also .as you do

roycruse · 19 August 2005, 12:28

STOP ! DONT SPEND 100 QUID

I have just spoken to 2 local steel merchants / suppliers.

There is no such thing as high tensile stainless steel.

There are 2 grades of stainless steel A2 and A4.

A4 is the marine grade stainless steel which just so happens to be higher tensile steel than the standards A2 but is not as high tensile as Hight Tensile steel.

It is perfectly possible that the mention of High Tensile Stainless is refering to A4 marine grade stainless.

Any way DUTCHY FASTENERS (01872 573999) (http://www.duchyfasteners.com/) have M12 100mm A4 Grade stainless bolts for around £2 each in stock.