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48' B31 head repair? #736424
05/24/18 12:20 pm
05/24/18 12:20 pm
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Posts: 130
boerne texas
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dean toensing Offline OP
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boerne texas
Hi there,
One of the ears on the intake manifold of my 48' B31 is cracked at the stud. What is the proper method to repair this?

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Re: 48' B31 head repair? [Re: dean toensing] #736435
05/24/18 2:21 pm
05/24/18 2:21 pm
Joined: Aug 2015
Posts: 1,268
Bolton Lancs UK
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Andy Higham Offline
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Bolton Lancs UK
Cast Iron can be welded but it is very difficult and may introduce more cracks.
What I would do is mount the head on the milling machine table and machine the outside of the inlet stub cylindrical, machine a groove in it and fit a rubber sleeve and spigot mounted carb


BSA B31 500cc "Stargazer"
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'35 OK Supreme
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Re: 48' B31 head repair? [Re: dean toensing] #736440
05/24/18 3:54 pm
05/24/18 3:54 pm
Joined: Nov 2011
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U.S.
Magnetoman Online content

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Originally Posted by dean toensing
One of the ears on the intake manifold of my 48' B31 is cracked at the stud. What is the proper method to repair this?
While welding with a Ni filler can be done, brazing it often a better choice. However, it's not possible to be sure without seeing a photo of the area around the crack.

Re: 48' B31 head repair? [Re: dean toensing] #736450
05/24/18 6:08 pm
05/24/18 6:08 pm
Joined: Nov 2015
Posts: 130
boerne texas
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boerne texas
Can't figure out how to post pics from my phone, don't have a computer (I know I know). The crack is along the centerline of the threaded stud. Starting to realize why I got a "good deal".

Re: 48' B31 head repair? [Re: dean toensing] #736453
05/24/18 6:48 pm
05/24/18 6:48 pm
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Posts: 130
boerne texas
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dean toensing Offline OP
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boerne texas
Well, I found another crack. I guess I need to look for a replacement. As I begin the search does it have to be a B31?

Re: 48' B31 head repair? [Re: dean toensing] #736473
05/24/18 10:24 pm
05/24/18 10:24 pm
Joined: Nov 2011
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Originally Posted by dean toensing
Well, I found another crack. I guess I need to look for a replacement. As I begin the search does it have to be a B31?
The have considerably different bores, and different part numbers for the heads so I doubt if a B33 head would fit. That said, I've never tried.

Your head very well could be salvageable. If you were just going to throw it away I would be happy to pay the shipping cost for you to send it to me in case I ever felt the urge to build a ZB31.

Re: 48' B31 head repair? [Re: dean toensing] #736484
05/25/18 12:19 am
05/25/18 12:19 am
Joined: Aug 2001
Posts: 134
Anchorage Alaska USA
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Mitch Online content
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Anchorage Alaska USA
let's see the cracks. there are options

Re: 48' B31 head repair? [Re: dean toensing] #736524
05/25/18 12:35 pm
05/25/18 12:35 pm
Joined: Nov 2015
Posts: 130
boerne texas
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dean toensing Offline OP
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boerne texas
It is a fine crack on the top side of the opening where the small cover gives access to the pushrods. I'm told welding cast iron is tricky?

Re: 48' B31 head repair? [Re: dean toensing] #736530
05/25/18 1:29 pm
05/25/18 1:29 pm
Joined: Feb 2007
Posts: 646
Ewing. NJ
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I recently had headwork done on a relatively rare cylinder head that included some pretty tricky welding. It wasn't cast iron, but the guy who did it for me has quite the reputation for complex welding and machining in the BMW and HD communities. His name is Randy Long and he is out of Pennsylvania, which although it is on the other side of the country from you, he does do things on a mail order basis. His prices are very reasonable. Only arguable downsides are, first, he is pretty popular and does the work in the order that it comes in, so he can have a pretty long back log. Last one I had done took 6 weeks. Second, he is very old school. No internet presence other than folks raving about his work on forums like these. No credit cards. I recommend him. You might want to give him a call: 610-286-5870.

Ed from NJ


Re: 48' B31 head repair? [Re: dean toensing] #736535
05/25/18 1:46 pm
05/25/18 1:46 pm
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Posts: 130
boerne texas
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dean toensing Offline OP
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boerne texas
Thank you very much!

Re: 48' B31 head repair? [Re: dean toensing] #736549
05/25/18 3:13 pm
05/25/18 3:13 pm
Joined: Feb 2014
Posts: 1,207
Lancaster, California
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Lancaster, California
Send it to Richter Machining - they did my B40 head. Great work!

Re: 48' B31 head repair? [Re: dean toensing] #736551
05/25/18 5:00 pm
05/25/18 5:00 pm
Joined: Nov 2011
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For what it's worth, the steps it should go through are:

1. strip the paint.
2. derust, ideally using a chemical solution that doesn't attack iron, and remove all carbon.
3. Magnaflux to reveal any additional cracks.
4. drill small holes at the end of each crack to keep the cracks from spreading when the head is heated for brazing.
5. braze.

The first two steps you can do your self to avoid having to pay someone to do it for you. Taking care of the third step yourself may reveal something serious (e.g. a crack between spark plug and valve seat) which would help you make an informed decision on whether to proceed. You could do #4, but the welder might not trust what you did and redo the drilling himself anyway.

Re: 48' B31 head repair? [Re: dean toensing] #736553
05/25/18 5:32 pm
05/25/18 5:32 pm
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Posts: 130
boerne texas
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boerne texas
Great info, thanks.

Re: 48' B31 head repair? [Re: dean toensing] #736587
05/26/18 3:41 am
05/26/18 3:41 am
Joined: Aug 2001
Posts: 134
Anchorage Alaska USA
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Mitch Online content
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Anchorage Alaska USA
once you braze, you can not weld... the braze contaminates the iron at the molecular level. its a good fix when it works (as is any fix when it works), but the deal is once you go down the braze rabbit hole, thats the only option unless you cut out all the affected metal and weld in new. braze also starts to lose strength at about 400 F. all that said, braze on cast is a legitimate repair

Re: 48' B31 head repair? [Re: dean toensing] #736597
05/26/18 12:22 pm
05/26/18 12:22 pm
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Posts: 130
boerne texas
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dean toensing Offline OP
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Found another head that is said to have no cracks but cylinder bolt threads are a little weak/loose feeling. Is it possible to fix that? Seems unlikely to me but I'm not a expert.

Re: 48' B31 head repair? [Re: dean toensing] #736616
05/26/18 4:53 pm
05/26/18 4:53 pm
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Originally Posted by dean toensing
cylinder bolt threads are a little weak/loose feeling. Is it possible to fix that?
Loose threads can be fixed with inserts like Helicoils or Keenserts. However, if it were me, and if I didn't want to risk being faced with significant work, I'd want to see photos of the valve seats to make sure they weren't excessively recessed.

Re: 48' B31 head repair? [Re: dean toensing] #736617
05/26/18 4:57 pm
05/26/18 4:57 pm
Joined: Aug 2001
Posts: 134
Anchorage Alaska USA
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Mitch Online content
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Anchorage Alaska USA
easy to fix bad threads. Helicoil or Timesert are the two big names and there are other copycats. repair kits are about $40 for SAE & metric thread. they are made in British threads but are harder to find & more money. these guys should have them ...

https://britishfasteners.com/

ha.... magnetoman beat me by 1 second

Last edited by Mitch; 05/26/18 4:59 pm.
Re: 48' B31 head repair? [Re: dean toensing] #736630
05/26/18 7:49 pm
05/26/18 7:49 pm
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boerne texas
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dean toensing Offline OP
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boerne texas
Would a insert give enough thread engagement to accomadate the head bolt length?

Re: 48' B31 head repair? [Re: dean toensing] #736633
05/26/18 8:35 pm
05/26/18 8:35 pm
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Magnetoman Online content

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Originally Posted by dean toensing
Would a insert give enough thread engagement to accomadate the head bolt length?
Although the threaded length of your 3/8" studs is 1" the rule of thumb is the threads only needed to be the same length as the diameter, i.e. ~3/8", in order to have full strength. "Full strength" means the torque would have to be considerably greater than allowed (which would be ~25 ft.lb. for a 3/8" fastener) before the fastener would strip.

Consistent with this, I have "Recoil" brand Helicoil-type inserts for British threads and they are available in lengths of either 1x diameter or 1.5x diameter (mine are 1.5x). Also consistent with this is nuts in all sizes are ~1d in thickness. Although the extra-long length of the threads on those studs allows for greater variation in stud length, head gasket thickness, barrel length, etc., I suppose nothing would keep you from tapping to a depth of 1" and using two 1/2" inserts in series if you wanted to be sure of super-strength.

Re: 48' B31 head repair? [Re: dean toensing] #736660
05/27/18 3:17 am
05/27/18 3:17 am
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boerne texas
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boerne texas
Any tips, suggestions on loosening the head bolts? Open end wrench seems kinda inadequate?

Re: 48' B31 head repair? [Re: dean toensing] #736796
05/28/18 8:47 am
05/28/18 8:47 am
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Sydney Australia
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As per MM's post, standard inserts are 1 D.
You can however get them in 1.5 D , 2 D , 2.5 D ( limited size range ) and 3 D.
I use 1.5 D most of the time as they seem to be a nice fit in gearbox & chain cases , 1 thread below the hole at the front and 1 to 2 threads short of coming out the other side.
Mechanics use 1 D usually as it allows you to fit them with a hand drill and have enough wriggle room to allow for it being slightly out of alignment.
The longer the insert the more critical the trueness becomes


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Re: 48' B31 head repair? [Re: dean toensing] #736865
05/28/18 10:24 pm
05/28/18 10:24 pm
Joined: Nov 2015
Posts: 130
boerne texas
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boerne texas
Great info, thanks. Any tips on loosening the head bolts? Open end wrench seems less than ideal.

Re: 48' B31 head repair? [Re: dean toensing] #736867
05/28/18 10:29 pm
05/28/18 10:29 pm
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Originally Posted by dean toensing
Any tips on loosening the head bolts? Open end wrench seems less than ideal.
In a catch 22, a ring spanner would be good, and you can easily use a ring spanner on the studs if the head isn't in place. But, if the head is in place you'll have to use open end.

Re: 48' B31 head repair? [Re: dean toensing] #736888
05/29/18 1:30 am
05/29/18 1:30 am
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boerne texas
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boerne texas
Thank you for the suggestions.

Re: 48' B31 head repair? [Re: ] #736903
05/29/18 6:11 am
05/29/18 6:11 am
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Originally Posted by Sluggo650PNW
Pipe wrench might work,
Dear god, no. If it's a joke, it's an inappropriate one since someone may may follow the advice.

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