The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: RichardL on 01.03. 2008 01:47

Title: Bad Head Skimming
Post by: RichardL on 01.03. 2008 01:47

Regulars among you know I have been talking about my engine (or much of it) being at the machinist. Well, I go it back and with considerable concern. Take a look at the pictures, below, which are the results of the skimming job done in this shop. To me, this looks like pretty bad work, and I have some experience with a mill. I don't believe that the most perfectly annealed gasket will be soft enough to fill the voids left by the cutter, particularly since aluminum is another soft metal.  Also, the barrels had similar problems, in some ways, worse, because there were high spots adjacent to the cylinders left over due to going north/south and east/west with the mill and not quite hitting the whole surface. I took a flat file to the top of the barrels and I suppose they will be OK. I have forwarded these pictures to the shop and am awaiting an answer. Even if he says he will redo it, I am not confident that that work will be better than my using a flat file or a piece of wet sanding paper layed on a perfectly flat surface. With the depth of these grooves, I don't think lapping will fix it. Any other thoughts on process?

I have also included a picture of the top of the head to show the result of the blasting job done in this shop. I thought I was going to get a textured, whitish and rough finish that has a classic look. Instead, I got this silvery look, which I don't like, but I guess I will live with it (on the crankcase, as well).

Making this more ridiculous is the fact that I chose this shop because it is supposed to be one of the best in the States, with a highly experienced and well-respected owner. I am not going to name the shop, for now. This shop also handled the grinding of my crankshaft, but I believe they sent that out to a crank grinding specialist, so, for now, I am not as worried about that (though I have yet to mic the journals).

Your thoughts and ideas are appreciated.


P.S.  If you folks happen to have seen the show "American Hot Rod", you may want to know that Boyd Coddington, "custom rod genius" and host of the show, passed away on Wednesday. Kind'a sad.

Title: Re: Bad Head Skimming
Post by: Brian on 01.03. 2008 03:31
Richard the silvery finish on the head should be easier to keep clean than a matt finish. As for the surfacing job, I'm not sure how to break the news to you gently!!!! It should have been done on a head surfacing grinder. He has obviously done it in a mill and to make it worse has used a end cutter. If he was going to do it in a mill at the very least he should have used a fly cutter which would have cut the whole surface in one pass. Any engine reconditioning place should have the correct machine to resurface the head so ask around. You could probably do it yourself if you have access to a surface plate and use fine wet and dry emery paper. Be wary of how much metal has been removed, you may need to use a thicker head gasket. If you are using standard compression pistons, around 7 or 7.5 to 1 you should be right but any higher and it would pay to check the valve to piston clearance. Over the years I have learnt to thouroughly check out any places before giving them anything. I have come across a few places that have had a good reputation but were useless. It will all be ok once you find the right machine shop.  Good luck.  Brian.
Title: Re: Bad Head Skimming
Post by: G/F DAVE on 01.03. 2008 08:52
Richard, Having looked at your photos of your cylinder head is the reason why I try to do as much as I can on my engines, but I am lucky as far as machining work is concerned my engineer is near 80yrs old but he cant be beat. He does all my crankshaft & rebores & his son does cylinder heads. As for your head I would try either using fine grinding paste mixed  with diesel on a sheet of glass,or fine emery on a sheet of glass. If using emery you can get bodyshop pads that are adhesive on one side stick these to your glass sheet then spray these with wd40 as a lubricant & rotate head thru a figure of eight pattern will take a while but I have had good results using this method in the past.You will have to cut emery pads to a straight edge & fit them together on your glass as most are round and designed for DA SANDERS. I would use a 240 grit then work my way to a finer grit as you get desired results. Use plenty of wd40 as this will help keep pads from getting clogged with alloy from surface of head. Hope this helps you I dont think I would take head back to your ( machine shop) though. *cry* Dave....
Title: Re: Bad Head Skimming
Post by: a10gf on 01.03. 2008 22:59
Sorry that you had to get this skimming result. Such "craftmanship" is totally inadmissible, to say the least. And I guess it's even worse than the photos depict. Go after whoever is behind, ask for some explanation, and welcome to post it all here. I had skimming done at SRM, they knew what they were doing, in contrast to whoever did the job shown on these pictures.
Title: Re: Bad Head Skimming
Post by: fido on 01.03. 2008 23:13
Why were the barrels skimmed? They don't usually get  surface damage.
Title: Re: Bad Head Skimming
Post by: groily on 02.03. 2008 17:10
What a shame and a pain Richard, and a professional disgrace frankly. Clearly, as stated, done with the wrong tooling - I could have done that on my own small miller (but wouldn't have) . . . I'm also not sure why he'd want to attack the barrels unless there was an obvious problem, like a burnt area, marks from moron's chisel, etc.
I just hope the guy had the head properly level when he attacked it, so that however flat it isn't, it's still truly horizontal.
Can't add anything to good advice already set out for sorting it, except to say if it were me I would COMPLAIN. I took a Jaguar cylinder head to a shop, also to be anonymous, in Ohio, which was highly recommended . . . not only did they do a terrible job with valves and seats, they messed up the bores for the guides for my new bucket tappets and also managed to bend the exhaust camshaft almost 30 thou out of true! But they did refund the job after a fair bit of ear-bashing and a letter from experts telling them why they should, so worth persevering. That cost them quite a lot of $$.
Not sure about valve to piston clearances . . .  thicker/double base gasket maybe easier than thicker head gasket? All depends really on how much the 'expert' has removed already. I'd guess you'd be OK . . . .but you need to know! Unless it really is a Rocky Horror Show the pushrod/rocker geometry should be well within limits whatever course you have to take, especially with, I presume, new valve seats in there. (I well remember one engine which had a mysterious ticking noise after re-cutting some valve seats quite severely - turned out to be the top of a tappet adjuster screw just kissing the inside of the rocker box lid: mea culpa!) And you probably could have a tiny fraction more taken off the cut-outs in hi-comp pistons (by someone competent). I have done that once in the past (not on a BSA), with no apparent problem and the pistons lasted a normal lifespan. Hopefully none of the above will be necessary.
Very best of luck. All will end well, but why is the road so often so arduous? Groily
Title: Re: Bad Head Skimming
Post by: RichardL on 03.03. 2008 01:24
Groily, et al,

I'm afraid that the idea of skimming the barrels was mine. My intetion being that the absolute minimum would be removed to achieve a level surface. If the surface was already level, then skimmng would remove nothng. I think my "machinist" (he no longer gets this revered title without the quotes) must have taken skimming to mean that some amount must be removed, regardless of existing flatness.

I am doing the measurements and drawing a model in AutoCad to see what the clearances sould be been piston at TDC and open valves. Because my rocker box is assembled, it is a bit hard to measure if the adjuster side of the rocker is the same distance from the shaft as the push-rod side. By logic, I think it probabaly is, but does anyone know for sure? By knowing this, I will know if the valve opening is equal to the cam lift. I will share the drawng with all when it is complete (if I don't get sick of it).

Title: Re: Bad Head Skimming
Post by: RichardL on 08.03. 2008 00:31
Asking the question:

Does cam lift = valve opening? Another way to put it: Are both arms on the rockers the same length?

Title: Re: Bad Head Skimming
Post by: PBMW on 08.03. 2008 01:02
Completely unacceptable.  Completely amature.
I build about 35 race motors (30 year old Japanese motors) a year.  I use a face mill on them on my Machine Center.  The "Good" news is he didn't take much.  You can feel comfortable takign another .005 or .008 if you need to to get it flat and true.  I wouldn't worry much about valve clearance as they were put together with about .100 clearance.  Also...Cam lift does not equal valve lift.  There is a rocker ratio that you need to pulg into your thinking.
I almost never machine a block.  If they did...measure for any taper between the two sides.
I'd also CC the head to make sure they didn't screw it up that way.
Shoddy workmanship is all I can say.
Sorry it happened to you...
Title: Re: Bad Head Skimming
Post by: flatdeck on 09.03. 2008 21:24
This is the stuff I hate to see, mainly because my engineering knowledge is limited and I'm not sure what to expect when I get a job done. I'm lucky that I have a v good friend helping me with my A7 who has oodles of experience building race engines and engineering generally. I guess one of the forums jobs is to sort out the good from the bad when it comes to suppliers? I dont think anyone should refrain from naming a supplier who has done a poor job especially when we are happy to name them when they have done a good one. I guess we are back to recommendations again ... best of luck with getting it sorted and getting a refund. Dave
Title: Re: Bad Head Skimming
Post by: RichardL on 10.03. 2008 02:01
Flatdeck, et al,

Thanks for the encouraging and supportive comments. For now, I am waiting for the "machinist" to return to his shop from Daytona Bike Week. Once he's back, I will see how he intends to resolve the matter. If he is apologetic and willing to do whatever it takes to make things right, then I would not feel right in naming him. Also, if I were to name him without first trying to work things out, he would have little reason to be agreeable. Rest assured, if he does not come through in an honorable and magnanimous way, members of this forum will be the first to know who he is, then, members of every other classic bike forum will know.

Title: Re: Bad Head Skimming
Post by: flatdeck on 10.03. 2008 03:03
Sorry if my post was taken as indicating one should complain bitterly without first seeking redress because I did not mean that. I agree that your man should have an opportunity to put things to rights. Cheers, Dave
Title: Re: Bad Head Skimming
Post by: RichardL on 12.03. 2008 18:12
So, the issue with the "machinist" is resolved. Money gladly refunded for skimming (so to speak) the barrels and head. Apparently, one of his help screwed up and tried to bury it. I believe this story. I think I have adequately fixed the barrels, and the head should be easier. I am not going to name the shop, as I actually like the guy, though, one of his other quirks is bad communications. He's an older gent (which is saying something, coming from me) and not up with computers. If there is anyone in the states who feels they must know who this is, to protect themselves, let me know and we can discuss it outside the forum. 

Title: Re: Bad Head Skimming
Post by: a10gf on 13.03. 2008 00:38
Good you got trough it without lasting damage.
...let me know and we can discuss it outside the forum.
Good choice.
Title: Re: Bad Head Skimming
Post by: RichardL on 22.03. 2008 08:03

Here are some photos after measures were taken to correct the sins done to my head and barrels, as shown at the beginning of this topic. The process was to run a flat file over the surface, taking away most of the high spots. Then, wet sand at 220 grit using WD40 as the lubricant, then, finish-up with 400 grit. The result is a really smooth surface without the kinds of imperfections that will lead to major compression leakage. I used a piece of polished marble floor tile as my surface plate; not bad for less than $4.00. Finally, I laid a precision-straight piece of steel (really, the back side of my digital caliper) across the sanded areas and tried to slip a 0.0015" feeler beneath it. I must say, I was surprised when the feeler didn't slip under at any point. Obviously, I have yet to blow out the filings and dust from the head.

By the way, thanks to all for the good tips and moral support.

Title: Re: Bad Head Skimming
Post by: groily on 22.03. 2008 22:44
Miles better - pretty sure to work just fine. Nice job (especially by comparison!) Onwards and upwards . . .