The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: morris on 09.03. 2018 12:06

Title: Cylinder head
Post by: morris on 09.03. 2018 12:06
Anyone ever had this kind of damage repaired (welded), and did it hold?
Title: Re: Cylinder head
Post by: A10 JWO on 09.03. 2018 16:32
I have seen this done with a valve insert fitted ( pressed in ), that was on a Ducatti Desmo. Can't remember any other details sorry.
Title: Re: Cylinder head
Post by: coater87 on 10.03. 2018 12:36
 I would think this could be repaired, but the cost of the repair is going to make it a no go.

 First you have to chase the crack out completely by grinding.

 Then heat the head to 400 degrees or so and let it soak at that temperature. This will help bubble contaminants out of the aluminum.

 Heat to 400 as a welding pre-heat, touch up all grind areas while hot right before the welding to make sure its as clean as possible.

 Tig weld with a harder rod (I forget the number) and make sure you have enough fill the first time.

 Back into the oven at 600, bringing the temp down slow to normalize the head.

 Now you have to do the machining, which will probably include decking the head because of warping, certainly new valve seat, and depending on where the crack goes you might have had to fill the spark plug hole completely with weld. So of coarse, drill, tap, and spot face the welded spark plug hole. You will also need to do some porting to clean up the runners and valve pocket.

 When done, you have a repaired aluminum head that might or might not hold. The only for sure thing is you will have a bunch of time and money stuck in it.

 I would either try and stitch pin it, which I am not even sure works on aluminum, or find a better head. Aluminum heads for these are not that rare, and a lot cheaper than a comparison Harley head from the same time period- plus you dont have to search out a correct date stamp.

 Lee
Title: Re: Cylinder head
Post by: muskrat on 10.03. 2018 20:21
G'day morris.
Being an iron head (Lee) it can be done. Finding a welder confident enough to do it is another story. It would need to be ground down the crack about 1/4". The head heated as per Lee's instructions then filled with an appropriate CI filler. Seat re-cut and spark plug hole re-tapped.
Cheers 
Title: Re: Cylinder head
Post by: coater87 on 10.03. 2018 21:16
G'day morris.
Being an iron head (Lee) it can be done. Finding a welder confident enough to do it is another story. It would need to be ground down the crack about 1/4". The head heated as per Lee's instructions then filled with an appropriate CI filler. Seat re-cut and spark plug hole re-tapped.
Cheers

 oh s%& its an iron head!  :o

 Im sorry Morris, I just assumed it was an aluminum head because you wanted to repair it.

 If you do decide to repair it, make sure whomever does it keys the braze in, so if it ever did let loose the bronze could not fall down into the cylinder. You would do this by grinding a slightly inverted V shape where the braze will go.

 I would not let anyone talk me into stick welding CI, it will make adding valve seats or trying to clean up your existing face almost impossible.

 Lee

 

 
 
Title: Re: Cylinder head
Post by: Black Sheep on 10.03. 2018 22:35
Iron heads are not exactly scarce. Easy enough to find a replacement.
Title: Re: Cylinder head
Post by: kiwipom on 10.03. 2018 23:16
hi guys, Morris i no it is no use to you but if you were here you could have any one of two that i have for free i dont think they are very rare so someone must have one that they could give you, good luck with it but i would not think of a repair, cheers
Title: Re: Cylinder head
Post by: RichardL on 11.03. 2018 00:33
This head, if not repaired, can still serve a very useful purpose: Fin donor.

Richard L.
Title: Re: Cylinder head
Post by: morris on 11.03. 2018 08:25
Many thanks for the replies and ideas guys.
I bought this head in good faith a couple of years ago on a jumble. It was packed in thick grease which made the crack invisible. I only noticed it now when cleaning it up. Back then I paid good money for it so I wouldn’t like to see it end up in the scrap bin.
One of the lads at work used to be a professional welder. He still has all the equipment so I might let him have a go at it and see what comes out.
I still got the old head which ain’t that bad. I just wanted to replace it because one of the rocker cover bolt holes has been (badly) repaired in the past. In the worst case I’ll be reusing that one, and look out for another head later.



Title: Re: Cylinder head
Post by: Triton Thrasher on 11.03. 2018 09:14
Iron head- I’ve deleted my load of rubbish.

You guys with your gleaming clean iron heads!
Title: Re: Cylinder head
Post by: Scott and Jay on 03.04. 2018 23:36
On my '58 iron head, there had been too many inlet valve seat grinds. So, they ground it wider and fitted bigger, Triumph, inlet valves...
Title: Re: Cylinder head
Post by: stev60 on 04.04. 2018 07:31
I have found a crack in the same place, the bike was running well before, and after valve grind even better, found a spare head, but wont be in any hurry to  replace, looking at the distance between spark plug hole and exhaust valve its a problem area if things get hot, or a new guide is pressed in improperly.
Steve
Title: Re: Cylinder head
Post by: Sluggo on 05.04. 2018 20:34
In the realm of slightly relevant but good FYI, Cracks like that are very common on Triumph Preunit alloy heads
(I realize this one is cast).  On the Triumph heads (I can post pix if you like) the cracks are usually on the exhaust valve side and go to/from the outer bolt holes into the seat area.
This is most distressing to Triumph owners and can also in some cases lead to leakage thru the bolt holes although some folks simply dont notice.
At one time, before I knew better I had a customer for my shop and he wanted to repair and keep the original head as it was a one owner bike.  We did all the repairs (Grind weld, new valve seats and guides etc etc), As far as I know it has held up but truth is I dont believe its ridden much (1957 TR6) but I recently spoke to the owner and his brother still has the bike. (Now 20 yrs later)

But I have since learned from John Healy, and validated by others (John has forgotten more about Brit bikes & epecially Triumphs than most mortals will ever know but every once in a while he is wrong) But its well documented that early alloy heads were very prone to this problem, and in some cases I have seen they crack on the intake sides as well.  But Triumph knew this as well and upgraded the heads with thicker castings and then adding a 9th bolt and eventually a 10th.
But amusingly, I now know LEAVE 'EM!!!!!!!!   Basically they all do that!  Much simpler fix is just leave the crack itself and carefully drill oversize the head bolt holes and then a slight intereference fit some steel tubing in them. (Heat the head, chill the tubes) and install those in place. This keeps the leakage from going anywhere.  Its unlikely the valve seats will come out or loose as well.
Or,, run a later model head.

Its interested to me HOW that head was cracked and if that is common, if not then how?  It IS possible a spark plug insert might have the same effect of the Triumph repair I outlined?  Regardless,, Cast Iron heads are not rare or hard to find.  Can ALSO use it for  a static display engine as well. 
Title: Re: Cylinder head
Post by: morris on 14.04. 2018 21:41
Had some good news! I contacted the vendor and he immediately offered to take it back and return the cash although I bought it from him nearly four years ago... 👍
One happy bunny here!