Small petrol engine - cylinder head bolt torque?

[robgraham]

I forgot when I posted some days back about my elderly cultivator engine that I would need to know approximately what torque to tighten the head bolts to. It's a Briggs and Stratton single cylinder, side valve petrol engine, 3.5 hp, possibly 1960's vintage. The block is aluminium.

Thanks Rob

[The Natural Philosopher]

"Not much" is as near as I can give you

More ally is damaged by stripping than by exhaust blowing out of it..

[Dave Baker]

Recommended bolt torques for a given thread and bolt material spec can be looked up on any number of web sites. GIFFS.

[Dave Osborne]

GIFFS? Not heard that one before...

"Google it for f*cks sake", I'm guessing?

[Rob G]

Well OK - but if you search on "torque aluminum steel" for instance, there are a large number of hits and they aren't really supplying the information in a way that I can understand. Perhaps you could be helpful and do a little bit of explanation for me please.

I ended up on this website

the first table, are the materials quoted there that of the bolt or the threaded body ? A bolt if over torqued breaks due to the twisting, whereas an over torqued threaded hole will strip out the threads and these, I would have thought, will not be the same for similar materials, so I'm not sure how to interpret this table.

Thanks Rob

[Clint Sharp]

In message , Rob G writes

Why on earth would you not google for 'Briggs Stratton head bolt torque'.

[Jules]

Tighten until threads strip, fit helicoil to resulting hole, then don't tighten as much the next time :-)

[Mike]

Briggs and Stratton have a lot of workshop manuals on their website for both current products and ancient ones. They are complete with dismantling and rebuild instructions, exploded views and torque figures, find something that looks similar in construction and use the figures they quote!

you'll more likely find it here

[Rob G]

aluminum steel" for instance,

Because I did so and couldn't make sense of the engine type numbering system, and reckoned that someone here would know the typical torque for steel bolts ( ~5/16") in Aluminium.

In fact for once this forum has not been as helpful as usual, and the answer hasn't been as rapidly forthcoming as I expected. It seems that the current attendees are all involved in house building and not the broader aspects of DIY.

Anyway with a lot of hunting around on the B & S website I found how to read the engine number, but that wouldn't produce a manual. An email query found another FAQ which showed torques for all engines, which I could then interpret having the engine number.

In the end the torque is the same as that shown on thelenchannel website for steel in aluminium, so it is a standard figure, which I had hoped someone here would have known.

Considering how many queries come up on this site which are a good deal less complex than this one, and never get told to go and hunt for yourself, I find it somewhat offensive that I got that answer. It would seem the answer is if the question is easy, then answer it and get your name in print, otherwise tell the OP to go and hunt himself.

Rob

[Rob G]

Thanks Mike - gave me the leads I needed. Interestingly in the end the torque of 140 in-lbs is standard for 3/8" steel bolts in Aluminium.

Rob

[The Natural Philosopher]

That sounds WAY too much.

10 stone on a foot bar?

[Clot]

Thanks, I thought my memory was at fault. Seem to recall doing BMCs to about

150 ft lbs. years ago which were not aluminium!

[The Natural Philosopher]

Im just looking in a haynes manual Cast iron cylinder head bolts 40lb ft

Oh, hang on 140 in lbs, that's about 12 lb feet!!!

Yup. That sounds more like it. Whoever did it in lb-inches!!

[Dave Baker]

Idiot.

[Clot]

Ah! So I had got it wrong, mixing the units, in lbs and ft lbs. Next time I root through the old tools in the back of the garage, I shall have to see what the torque wrench units were!

[Jules]

Hmm, shame they only list model numbers - we've got a B&S 10HP/362cc

4-stroke in our mower*, but there's no data plate on it to tell us what model it is (and I'm not sure I fancy downloading every pdf file on the B&S site just in case :-)

• leaks oil like a sieve and needs a new crank seal - if I had the manual I'd strip it all down and give it a general once-over too, though.

cheers

Jules

[Rob G]

Guessed you must have fallen for that one !!! A 12x overload would have qualified for the suggestion of tightening to pull-out and then install thread inserts !

Interestingly all the B & S tables are in in-lbs (rather than lb- ins!!), so that must be a 'Merican thing.

Fortunately the only torque wrench I have is a 1/4"socket one calibrated in Newtons and in-lbs.

Anyway the motor (ooops engine, been reading too many US websites) still doesn't work but I suspect my messing around has also got muck in the carb. Hey-ho!

Rob

[Dave Liquorice]

B&S are American...

[Clot]

Fortunately, despite having stripped and rebuilt many an engine, I've never sheared a bolt or stripped a thread, (at least not a critical one that I can recall)! Argh, it's got me thinking of the number of Maxi crankshaft oilseals I've replaced in years gone by. Got to the stage where I could replace one at the roadside in three quarters of an hour!

[Dave Liquorice]

The guide on "where to find the engine/model" number doesn't help? My B&S doesn't have a nice plate, the numbers are just stamped into one of the castings.