The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: orabanda on 18.01. 2014 13:21

Title: Alloy head bolts
Post by: orabanda on 18.01. 2014 13:21
Hi All,
Can someone please supply the lengths of the bolts which make up a set for (a) a 1954 A7 SS, and (b) a 1958 A10 Super Rocket?

Should all or some of the bolts be of a "waisted" type?

Thanks,

Rickity Dick
Title: Re: Alloy head bolts
Post by: muskrat on 19.01. 2014 01:16
G'day mate, the SS and the SR are the same length, the longer 6 are wasted. Sorry can't help with measurements right now.
Title: Re: Alloy head bolts
Post by: wilko on 19.01. 2014 23:16
I wouldn't recommend alloy bolts as they will keep stretching each time you re-torque. Steel is better.
Title: Re: Alloy head bolts
Post by: Rocket Racer on 19.01. 2014 23:43
I wouldn't recommend alloy bolts as they will keep stretching each time you re-torque. Steel is better.

brilliant  *yeah*
Title: Re: Alloy head bolts
Post by: RichardL on 20.01. 2014 12:53
Richard,

I assume you have no question about the part numbers. It seems that Burton Bike Bits http://burtonbikebits.net  lists bolt sizes on their price list. My A7 and A10 are both apart right now, so I will try to get measurements off of the actual bolts this evening.

Richard L.
Title: Re: Alloy head bolts
Post by: trevinoz on 20.01. 2014 23:01
Richard, (Rickity)

Head bolts are:-     Long, waisted - 3", original bolt- 13/16" thread, pattern- 1" thread.
                           Medium, waisted, 2-5/8', original- 7/8" thread, pattern- 1" thread.
                           Short, plain shank, 1-5/8", original- 11/16" thread, pattern- 1-1/16" thread.

We shall see if Richard L's measurements are the same.

I suppose it's a matter of time before they call you "wrinkly".

Trev.
Title: Re: Alloy head bolts
Post by: RichardL on 20.01. 2014 23:24
Better than "shriveled".
Title: Re: Alloy head bolts
Post by: orabanda on 21.01. 2014 03:10
Trev,
As long as they don't call me late for lunch!

You are a gentleman and a scholar, but just a tad too cheeky; a typical Eastern sider

As for you, manosound: - Thanks as well!

Richard
Title: Re: Alloy head bolts
Post by: RichardL on 21.01. 2014 03:56
Richard,

Here are the dimensions of my head bolts shown in the photos. I didn't follow good engineering practice because the number of decimal places isn't consistent, but I think you will get past that. Obviously, I didn't round to nominal dimensions (like, in 1/16 ths of an inch), but just entered the caliper readings for the one bolt measured of each type. The A10 bolts should be correct stock or replacements. I think the bolts from the A7 are stock or correct replacements also, but I really don't know yet, not having gotten too much into it since purchase in November. Also included is a picture of the head of one of the A7 bolts where "Wiley R" is formed. I would be interested to know if anyone is aware if this signifies an original part.

Richard L.

P.S. The drawing is something of a mess because of using the A10 seat as a photo table. Sorry about that.
Title: Re: Alloy head bolts
Post by: trevinoz on 21.01. 2014 20:11
Richard L.
                  Wiley bolts were original fit. Quite a few heads about the bike were so marked.

Trev.
Title: Re: Alloy head bolts
Post by: bikerboy on 19.02. 2014 03:28
I have found this useful in the past

http://stainlessbits.com/link12.html

You look for the part number of the bolt/nut and it gives you the spec
Title: Re: Alloy head bolts
Post by: beezermacc on 04.03. 2014 00:10
I find that the head bolts supplied by the likes of MCA and Wassell are too short. If you measure the depth of the aluminium plus the depth of the threads and add about 2mm for the thick washer you'll find that the bolts supplied are about 8-10mm too short. I've come across a few people stripping threads recently. I have obtained some high tensile socket cap bolts which I have cut to the correct length to ensure using all the available thread in the barrels.
Title: Re: Alloy head bolts
Post by: bsa-bill on 04.03. 2014 09:12
Quote
correct length to ensure using all the available thread in the barrels.

I think this is maybe not so good, how do you know if your clamping or bottoming
(plus if my last project is any guide there needs to be room in there for POs accumulated crud, not that anyone here would allow that to happen)
Title: Re: Alloy head bolts
Post by: Briz on 04.03. 2014 11:04
I find that the head bolts supplied by the likes of MCA and Wassell are too short. If you measure the depth of the aluminium plus the depth of the threads and add about 2mm for the thick washer you'll find that the bolts supplied are about 8-10mm too short. I've come across a few people stripping threads recently. I have obtained some high tensile socket cap bolts which I have cut to the correct length to ensure using all the available thread in the barrels.

Yes, I've found this. Especially the shortest bolts. Inadequate thread engagement.
The way to avoid bottoming out is to test & measure.
I too used top use quality allen bolts, but harder to find now in BSF threads.
Title: Re: Alloy head bolts
Post by: beezermacc on 04.03. 2014 21:29
Quote
correct length to ensure using all the available thread in the barrels.

I think this is maybe not so good, how do you know if your clamping or bottoming
(plus if my last project is any guide there needs to be room in there for POs accumulated crud, not that anyone here would allow that to happen)

I run the bolts down into the barrels without fitting the head, measure the free length under the socket cap and compare this with the depth of aluminium of the cylinder head. Obviously it is necessary to do this sort of check when using non-standard parts, but better than using the commercially supplied stuff which is too short and leads to stripped threads.
Title: Re: Alloy head bolts
Post by: duTch on 05.03. 2014 09:57
Quote
. I have obtained some high tensile socket cap bolts which I have cut to the correct length

Heartening to know...!
 When I originally threw mine together in '79-'80, I used socket caps ( BSF reasonably available then), mainly 'cos finding proper ones at the time was nigh on impossible in my neck o' the woods.
 
On the last build, I wasn't too sure of the socket caps integrity, the unthreaded diameter, or lack of 'waist', so replaced them with 'proper' ones, maybe from Burtons (?), but the lengths were a bit shorter than I'd liked, but haven't caused any trouble (low 7.25 comp.)
 I also tap and air cleaned holes and threads , (blast beads everywhere), and now worth noting the cavity between the sleeves and around the pushrod tunnel was completely clogged.
Title: Re: Alloy head bolts
Post by: BSA_54A10 on 09.03. 2014 05:43
I can not see the point of using waisted bolts on these heads.
the usual reason is to allow the bolt to snap before the thead strips.

Also if you use allen headed bolts nearing down onto alloy it is essential that you put some really thick washers ubderneath the heads or they will sink into the alloy.
Title: Re: Alloy head bolts
Post by: duTch on 09.03. 2014 09:00

 Noted Trev, I had reasonable washers under socket caps, but maybe not as robust as their tensile replacements.
 Other thing, I think the shanks of the waisted bolts are a touch thicker, so there's less lateral slop and the head sits a bit more 'precise' (weeeell... *????*)
 cheers
Title: Re: Alloy head bolts
Post by: Briz on 09.03. 2014 10:27
The point of waisted bolts is that the required stretch that provides the clamping force is spread over a length of shank rather than being concentrated at the root of the last bit of thread, which on an un-waisted bolt is the weakest point.

You need good washers under any head bolt on an ally head. There isn't really much difference in under-head area between allen bolts and hex-heads.
Title: Re: Alloy head bolts
Post by: BSA_54A10 on 11.03. 2014 22:40
The surface area under an allan bolt is 10% less than the  inner  base circle of a hex head.
While that is a very small number, it makes a massive difference to the compressive pressure under the head sufficient to create a shear plane under the head perimiter.

As to waisting , I am aware of the theory however in practice bolts fail in torsion, not tension.
With only hand tools there has never been a man strong enough to stretch a 3/8" bolt pasts it's elastic tensile limit.

Back in the real world.
The head bolts on an A series are so lowly tensioned that in most cases you can get by with good quality ( not Chineese )  grade 5 bolts.
My diction was probably not the best what i waa trying to say is "I Don't see the need for waisted bolts in this application "
Title: Re: Alloy head bolts
Post by: Briz on 12.03. 2014 23:09
Well, a 3/8 allen bolt has a 9/16" head diameter. 3/8" hex bolts have a 9/16" hexagon. OK; BSF ones are a tiny bit bigger.
But my advice was that thick-ish washers should be used under both. Its not good practice to install head bolts into an alloy head  without washers on any engine.

And as regards the stretch, I wasn't talking about bolt failure, I was talking about normal usage. For best clamping, a bolt must be stretched a certain amount. That stretch will occur at the bolts weakest point. Without the waisting, thats all concentrated at the root of the thread.

Isn't the stock head bolt torque about 32 ft-lbs? Thats a fair amount and probably enough to stretch a grade-5 bolt as far as you'd want to. The stretching info above applies to any bolt regardless of tensile strength. It'd still be safer waisted.

A torque wrench is a normal hand tool. I found 90 ft-lbs was enough to break a 10mm stud! It broke at the thread root.
Title: Re: Alloy head bolts
Post by: RichardL on 13.03. 2014 01:55
Back in 2008, some "Richard" guy posted the following, which he had found while trying to figure out head bolts.

The follwoing (about head-bolt shank diameter) is quoted from Roland Pike as found at http://www.restorenik.com/daytona/RP_chp_22.htm:

After a year we had improved the port configuration and it ran so much better with one big carb that the twin carb option was dropped. We had found it useful to measure the capacity of the inlet ports and check on performance, about 142 to 150cc's gave optimum results. If an engine was down for power we often found the ports undersize.  Like all aluminium cylinder heads, these expanded a lot with heads and at the outset we experienced stretched or broken head bolts. These bolts went downwards through the head into the iron cylinder block and would usually break at the root of the last thread, which was the weakest point because it took all the stretching. To overcome this we quite simply put the bolts in a lathe and reducing the diameter of the pIain portion to 10% less than the diameter of the root of the thread. This meant that the thread was no longer the weakest point and that the plain portion could stretch without exceeding its elastic limit.

This was completely successful on the first attempt and no more trouble was experienced with the bolts. They could stretch when the head expanded and return to their original length as the head cooled own. When the new twins were going into production however, Alan Jones who was Works Manager at that time phoned me to say they were unable to make the head bolt as needed, despite my pointing out that we bad found them necessary, he just continued to say they were unable to make them. I went on with my work and forgot about the matter, but I did not have to wait long, within a few hours the motor cycle test shop foreman was on the phone to me complaining the head bolts of the new twins were breaking right and left, so I referred him to Alan Jones.  Mr Jones reiterated they were unable to make the bolts we had designed. Prior to this last call I had taken the precaution of calling the drawing office to say that Jones would not follow their drawings of the bolt thus securing an ally. Alan Jones got no sympathy when he had to pull all the bikes concerned back, dismantle the engines and use the bolt we had specified.

The following is copied from: http://www.enginehistory.org/british_fasteners.htm

Bill Allan adds "It should also be stated that some of the early nuts would have been machined from round stock, with an integral washer, so round bar stock sizes would have been involved in calculations. One other problem is that the original Whitworth heads (AF) were too large relative to the actual bolt shank, (that's why spanners/wrenches are the length/size they are: so you can't apply to much torque. In the first part of the 20th Century, the head sizes were reduced to the size one below. (British Standards specify that the AF measurement of any bolt not be greater than 1.75 that of the shank: 1/4 inch Whitworth is almost bang on the button) This causes even more problems when you need replacement Whitworth fasteners, for machinery over a 100 years old. It's also the reason why some old spanners/wrenches have two Whitworth numbers on them."