Oil leak at the head gasket

Mark said:

now that I think about it...... I had a BSA A10 that had turned down head bolts.
pretty sure that they were stock.

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Yep,
and if you look at most aluminum engines you will see studs and bolts that have been machined in some way to increase the stretch-ability of the fasteners and spread the stretch over a larger area.

If you stretch a bolt without the undercut, most of the stretch would occur in the short threaded section of the bolt that was not screwed into the hole. That section of the bolt would break before the larger shank of the bolt would stretch very much.

That is why rod bolts are always undercut. Nearly every bolt in a Mercedes engine is undercut.

Actual torque to yield bolts are a little different and require a specific design for the application. They do stretch beyond their ability to return to the original dimension and can only be used a set number of times before they are discarded. Some can only be used once.

Many cars seem to have head bolts with a fast helix on the shank. These are only meant to be used once. Also, I remember speaking to Norman Hyde years ago, & he said that the head bolts on the triples were of a particular grade of steel to allow a certain amount of stretch. I wonder what the minimum order on specials is at ARP?

That's amazing analysis and work. Basically you are holding the head down with very stiff springs.
It seems like ARP should make waisted bolts available from new or maybe they will make them on custom order. Most of us don't have that 4th axis available.

Jaydee

Jim

Thanks for sharing this amazing discovery. I know there are a lot of engines that use bolts and studs that are waisted for this reason. I had always thought that on the Norton that the bolts were short enough and thin enough that this was not the problem. Probably the shortness is actually part of the problem.

Do you think that if the bolts were waisted in a lathe and then polished to a mirror finish that they would be retain their full strength. I think probably they would and that is something I could do myself. I have been sticking with solid copper gaskets on my 850 because I am cheap and I like re using the gaskets. I was just about to switch to the Andover fire ring gaskets that everyone else says are best.

I was about to try some of the ARP washers because I had noticed the holes getting smaller. I had also noticed that when I drilled the holes back out that the problem got worse. I guess nice thick large diameter washers will still be necessary.

Nigel

Ron Wood used steel inserts in his Norton heads. Not sure why he used the cupped shapes instead of flat washers.



He didn't, however, use waisted bolts. Jim is the first one I've seen do so.

ARP make a variety of waisted/undercut/reduced shank head bolts and main cap bolts, in both metric and SAE threads. I'm planning to visit them and see if they have off-the-shelf bolts in that design that will fit the Maney 1007 engine I'm building, which uses metric size head bolts. They will also make custom fasteners to order, but I don't think I'll go to that length. If they don't have something in stock, I'll probably just modify the ones I have. Lots of good tech info on fasteners on the ARP web site at http://arp-bolts.com/ . Their downloadable catalog is a great tech reference. Their production head bolts come in 185,000 psi tensile 8740, 200,000 psi tensile 8740, and 170,000 - 190,000 psi stainless. They will make custom head bolts in materials with much higher tensile strengths, but that's not needed for most of our Commando applications.

Ken

tricatcent said:

Jim

Thanks for sharing this amazing discovery. I know there are a lot of engines that use bolts and studs that are waisted for this reason. I had always thought that on the Norton that the bolts were short enough and thin enough that this was not the problem. Probably the shortness is actually part of the problem.

Do you think that if the bolts were waisted in a lathe and then polished to a mirror finish that they would be retain their full strength. I think probably they would and that is something I could do myself. I have been sticking with solid copper gaskets on my 850 because I am cheap and I like re using the gaskets. I was just about to switch to the Andover fire ring gaskets that everyone else says are best.

I was about to try some of the ARP washers because I had noticed the holes getting smaller. I had also noticed that when I drilled the holes back out that the problem got worse. I guess nice thick large diameter washers will still be necessary.

Nigel

Click to expand...

Nigel,
I have not tried waisting the bolts in a lathe - I was advised against this by an engineer at ARP.

But who knows -it may work if the machining marks were polished out by polishing in the lengthwise direction.
Jim

How much do you waste them over what length, must be an equation from an engineering perspective? A complete re-think on the fasteners when using dissimilar metals al-la crankcase/barrels/head on these Nortons perhaps. Could an engineering student do a thesis on this subject? Could it be done by simply drilling the studs and surface finishing the bores?

lcrken » re: the Ron Wood method: how thick (deep) are the cups? You have to look carefully to note that they are cupped.
I am not sure that Jim enlarged the size of the washer and the area it sits on or not. If the washer is hard and the area big enough
will that not preclude compressing of the alloy head metal? Could you then, after insuring you have clearance in the bolt hole, use
some sort of wave washer to maintain tension of the bolt?
Just wondering...

May I add this out of general interest to the discussion:

http://machinedesign.com/fasteners/intr ... 29c6a94e87

Onder said:

lcrken » re: the Ron Wood method: how thick (deep) are the cups? You have to look carefully to note that they are cupped.
I am not sure that Jim enlarged the size of the washer and the area it sits on or not. If the washer is hard and the area big enough
will that not preclude compressing of the alloy head metal? Could you then, after insuring you have clearance in the bolt hole, use
some sort of wave washer to maintain tension of the bolt?
Just wondering...

Click to expand...

The washer can not get very much larger on the center hole and the RR hole near the oil return passage.

I have tried spring washers. By the time you get a flat base washer and enough spring washers to handle the load a longer bolt is required -and it looks a bit strange.

Waisted bolts will be available soon through CNW. Jim

comnoz said:

Waisted bolts will be available soon through CNW. Jim

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Oh, yes!!! I like the sound of that!!! 8)

comnoz said:

......Waisted bolts will be available soon through CNW. Jim

Click to expand...

Boy O Boy, Is this awesome or what! There has never been a better time to own and ride our bikes thanks Jim

I think when CNW has them I will just buy them from there. That way everything will be perfect. Until then I will just let my bike leak a bit as it always has done.

I use only copper head gaskets. I use triangular reduced shank bolts/studs and I have not had a leak or any weeping at the H.G. for years (adding .005” copper wire and gasgacinch sealer around pushrod tunnels). The photo below has been on my webpage for everyone to see for years now at:

http://www.jsmotorsport.com/technical_compression.asp

This photo also goes out in my H.G. instructions. It shows the bolts I have been using and also answers Kens question about studs. These bolts were available cheap (in limited sizes).



Instead of being reduced in diameter they have triangular shanks - effectively reducing the material at the shank so the bolt will stretch and give the desired spread out elasticity. This works well because the outside corners of the triangle helps align the bolts in the bolt holes and resists twisting/breaking on assembly/disassembly. If you need to machine your own bolts then you can machine the flats along the shank by using the side of a cutter and end up with a radius at the end of the cut. Your machine marks will be parallel with the length of the bolt and not create stress risers. And its much easier to do. I don't advertise these bolts but they are available with JS rebuilds.

What I am saying is that I have already tested them with success for years in real life conditions with no failures. I am not advertising here, just clarifying and showing everyone an easier machining technique (& cheaper bolt) that will give the desired results.

That's interesting, Jim. I've never seen triangular shanks before. Is that a standard form for some particular (aerospace?) application, or just something you came up with?

Ken

That is very clever, I like it. I also think that Mr. Sparks had a great idea of having this problem addressed by an engineering student as a Master's thesis. They often need an interesting and real world problem to address and are often quite young and haven't had enough experience in the outside world to know what problems to address.

jseng1 said:

........ I use triangular reduced shank bolts/studs ........ I have already tested them with success for years in real life conditions with no failures. I am not advertising here, just clarifying and showing everyone an easier machining technique (& cheaper bolt) that will give the desired results.

Click to expand...

Heck Jim, I never knew these studs even existed, thanks for posting this info, sounds like a great option. I think you ought to list them separately on your site. I can't see any problem with "quote - advertising" , or mentioning this kind of stuff here, shoot Matt ran a whole thread on his new electric starter product, listing when it would be available etc... We're all enthusiasts here, what better place to talk about things that make our bikes better (not to mention life easier).

The first batch of waisted head bolts is now running.
I should have them back to Matt in about a week. Jim

[video]https://www.youtube.com/watch?v=zkfLr9MZlCk[/video]

Arghhh. And I just bought a set off of Matt recently and have them waiting for my head. :-(

gortnipper said:

Arghhh. And I just bought a set off of Matt recently and have them waiting for my head. :-(

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Well, I could swap you out.