The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: coater87 on 05.06. 2009 17:05

Title: Crankshaft pinion
Post by: coater87 on 05.06. 2009 17:05
 I have tried and tried to remove this, did a search on the forum and didnt find anything.

 Is there a trick to pulling the oil pump drive pinion off the crank? With the puller I am using, I am worried I will either break the pinions thin ears off, or crack the case trying to pull off from behind. Am I missing something completely here?

 Can I split the cases with this still on then worry it off on the bench?

Title: Re: Crankshaft pinion
Post by: Lannis on 05.06. 2009 18:46
Yes, that's the way to do it, on the bench.

Check out this link for more info:

Title: Re: Crankshaft pinion
Post by: coater87 on 05.06. 2009 20:15
 Thanks Lannis!

 That worked out great, I split the cases and just easily drove the pinion off the crank.

 Now to to get at the trap plugs, clean everything up well and see what we have to work with here...

Title: Re: Crankshaft pinion
Post by: RichardL on 05.06. 2009 20:25

The removal of the sludge-trap plugs can be a hair-pulling-out event. I used the procedure described in the fifth paragraph of the document Lannis sent you and it worked great. It shouldn't matter if you drill all the way through, presuming you are going to replace the plugs with the superior hex-key type.

Richard L.
Title: Re: Crankshaft pinion
Post by: coater87 on 05.06. 2009 21:14
 Hi Richard,

 I see the "ill fitting screw-driver gang" was after these too. They never thought to try anything funny with the puch marks though, so thats good- but they really did round over the rod bolts, now how did I know that?

 Either I am psychic, or just put 2 and 2 together after seeing the other rebuild mods thay tried... *conf*

 I am feeling more confident in this engine by the minute, its a nice clean design. Besides all the shot bolt holes, more then likely bent cam (356), I am not seeing any damage I dont believe I cannot over-come here. And a big plus is the cases match.

 The real challange will be to find good to excellent quality replacement parts, being new to a BSA motor and not having dealings with any suppliers- and seeing how many of these guys THINK they have good quality stuff- thats my big worry. Once in a while I read where even a big name supplier offers garbage.

 When it comes to replacement parts, I am going to have to reply on this boards experience quite a bit. Like here is the first, where can I find good quality pistons at 7.25:1 on standard or +10 if need be?

Title: Re: Crankshaft pinion
Post by: coater87 on 06.06. 2009 17:13

 Maybe the +10 part sounded odd- +20, +40, etc. is more standard issue. But here is my thoughts, I believe my barrels will clean up nice with a .25 MM bore- really just removing some very light pits and very shallow scores, and of coarse the ring lip and skirt belling.

 My idea is to copy what the auto racing guys do when a block cannot be sleeved because of rules. Get my barrels bored .25 MM instead of .50 MM, and run a +20 piston through the engine lathe effectively making it +10. I think this would save my barrels by not removing good material, just like one would do on the timing side bush.

 I also do home shop machining, and cutting the pistons, and cleaning the lands should not be too big of a problem.

 I am thinking a +20 set of rings would be best, then file to fit. I dont know how tight a set of rings from somewhere like JP is, so buying a STD. set may be false economy- or does anyone have thoughts that a STD set would be big enough not giving to much gap.

 Maybe this is a rambling, but honestly my thoughts are to save the barrels here. They are not too easy to find, and not usually cheep when you do. Boring is less expensive then sleeving, and I just am not big on a sleeve if I dont have to fit one. I think "half boring" would be a good way to accomplish quite a few things here if its do-able.

 Let me know if I have fallen off the edge here.


Title: Re: Crankshaft pinion
Post by: MikeN on 06.06. 2009 20:04
Hello Lee,
  i was interested to read your comment about using an "engine Lathe" for machining pistons.What is this machine?
  Im guessing its for turning piston diameters  oval to relieve the non-thrust faces?
  How does it work?
  Ive just measured some pistons and they typically have about a 6-10 thou relief on the sides. Im curious how you achieve this.
Title: Re: Crankshaft pinion
Post by: BSA_54A10 on 07.06. 2009 00:42
You can run with round pistons but they will wear quickly and you need to give them a bit bigger running clearences.
Total Seal will supply you with a set of standard or gapless rings which I recommend 100%.
Just tell them your bore , ring width & depth and that you are running it on a chill cast iron bore.
Title: Re: Crankshaft pinion
Post by: coater87 on 07.06. 2009 06:51
 Hi guys,

 Maybe I am going to far with this, on the second thought train.

 Mike, all we ever did was turn the piston down, first clamping the skirt and turning everything above the first land, and cleaning the grooves before we moved the set-up (pulled the ring pins first). Then flip the piston around and clamp above the first land, and turn the skirt. Crank the taper in and turn everything below the gudgeon boss with a very slight taper- not the right way I know, but easy. We didnt do anything special to get the correct oval shape. But after they cut most of the skirt ears off to lighten the load, there was not a lot left to taper anyway. And yes, we blew up a fair share of motors.

 I am not a professional machinist by any means, what little I know I learned from a guy who was not a professional either! *conf*

 I wonder if you could do this the correct way with a rotory table and an angle plate on the mill? I have never tried it. Oh yeah, engine lathe- sorry about that, its just what I call a non-wood lathe. I have a couple other odd hobbies besides this.

Title: Re: Crankshaft pinion
Post by: MikeN on 07.06. 2009 09:56
Thats interesting,Lee,
 I think I would stick to commercially produced pistons on a bike.
When I have worked on pistons I always make a jig which consists of finding or making an eye-bolt or lifting eye that the gudgeon/wrist pin fits through. You then mount a bit of steel or alloy bar in the lathe that is slightly bigger than the diameter of the piston.Most pistons have a turned recess in the base of the skirt.So you machine a shoulder so the piston is a good fit on the bar.Tap a female thread to accept the eye-bolt and you can then screw the piston onto the jig .
  This holds the piston securely and concentricly and you can machine all over the outside, if required, on one setting.
  It occurs to me that you could then transfer it a 4 jaw chuck and off-set it  a few thou to the left and right to obtain side clearance.
  But im sure it would be much better to obtain some nice new shiny Plus .020's
Title: Re: Crankshaft pinion
Post by: trevinoz on 07.06. 2009 23:35
Lee, you will be extremely fortunate if you clean up your bores with .010".
For the amount of stuffing around to machine .020 pistons to .010 I feel it is not worth it.
You will probably find pistons are cam ground for the side clearance. The idea of filing .020 rings to .010 is not good either. The rings are precision manufactured to a diameter and you will be effectively changing that and will not get perfect contact on the whole diameter.
Title: Re: Crankshaft pinion
Post by: RichardL on 08.06. 2009 02:58
So, are all motorcycle pistons formed oval? And is that only south of the lands?

So, Lee, it does seem that 0.010" over at he pistons is not practical.However, I think the same logic of "conserving the metal" can readily be applied to the small-end crank bush, grinding to cleanup then reaming the bush to fit. I'm not 100% sure, but I think this requires the solid phosphor-bronze bush if you are between common regrind diameters.

Richard L.
Title: Re: Crankshaft pinion
Post by: coater87 on 08.06. 2009 06:27

 It is south of the pin boss I think and on a diesel I believe south of the last land if it has oil control below the gudgeon.

 These are oval for splash oiling the cylinders below the pin ends proper, I believe this is why the stock pistons have splash oil holes fore and aft (minor thrust face), because those are not tapered faces and the holes are their only means of oil.

 Talked to a buddy at work who still is into racing, but now its grass drags on snowmobiles. He asked if these were cast or forged pistons, (also new or used). I told him cast-used just for kickes, and about 2 inches in diameter. Off the top of his head he figured we would need to trick the lathe into thinking it was turning something around a 10 or 11 inch diameter to get the proper oval shape, and even then it would not be as good as a factory piston. I guess those are more of an elipticle (sp?) shape- much smoother then we could do on a lathe set-up. And doing hand touch up would be difficult, and you would never get them exactly identicle- which would make balancing harder depending how far off of identicle you are (among other problems like having to much clearance).

 After talking a while, he told me we got away with hacking up pistons turning a taper on the entire skirt because we didnt really expect them to last that long, and nothing did- be it a piston or rod or valve spring or whatever, something was always going south.

 Then he started talking custom pistons, he says he has paid 6-8 hundred for a set (snowmobile) and I might pay much more IF I could find a company to do it. I imagine the price has a lot to do with how many sets of a certain type of piston they sell- I cant see +10 pistons for a BSA golden Flash being a huge seller, so the price may reflect that in a big way.

 After the talks with you guys, and the guy at work I know I am better off just going stock +20 even if it does waste a little barrel- I want a decent running cooking grade engine- and I want it to last. I think spending $800.00 (at least) on a good set of +10 pistons trying to save a $500.00 set of barrels is going backwards. But the discussion was interesting! *smile*

 Now for another odd "what if"- the oil pump on these bikes runs at 3:1 right? If this could be changed to 4:1, would this increase oil pressure just because of flow restriction? Like trying to jam 10 gallons of water through a drinking straw in a hurry, or would you just have a faster flow rate? What about seals and gaskets, if the flow/pressure is increased would these handle it? Or, does the ratio not matter, its all in the impellor size?

 (the things I think about when NOT thinking about stripped out bolt holes!)


Title: Re: Crankshaft pinion
Post by: bsa-bill on 08.06. 2009 13:26
Hi Lee
running the pump faster? flow has got to be faster surely ? - I don't know to be honest, but the pressure will not be greater as the pressure release valve controls this to 60 lbs/inch

How are you going to gear it up BTW

All the best - Bill
Title: Re: Crankshaft pinion
Post by: coater87 on 08.06. 2009 15:18
 Hi Bill,

 I dont know either, but thanks for thinking about the pressure relief valve. I guess if thats working correctly it should be impossible to blow the gaskets or seals.

 This all came about because I know my oil pump has a "few" problems- I have not taken it apart yet but someone did, obvious by the blue crud and chewed screw slots. It turns very easy (I dont think its supposed to do that) for about 10 turns then locks solid. I have to turn it in reverse to free it up again. Who knows what I will find in there... *sad2*

 I took a look at SRMs pump, and looked at the chart of oil pressure they have. A good increase across the board. Now I have never seen one in person, but if they kept the pump body the original size, how did they increase the pressure? Just because it was made on a CNC Mill/lathe wouldnt do it, and certainly the blue anodising doesnt help that much ( *smile*), so how?

 I would think that increasing the ratio to 4:1 would increase the low RPM pressure, and all pressure across the board- but then guys with a tach would get screwed up- so is it impellor size?


Title: Re: Crankshaft pinion
Post by: RichardL on 08.06. 2009 15:39

Without going into the oil delivery differences, which I think might be irrelevant or, even, desirable, I think you are back into the issue of costly or tricky machining to reach the end. You would have to create a new worm drive and pump driven gear.  I don't know if you are doing this to accomodate a 4:1 tach, but I think you could get a chronometric 2:1 from Nisonger or one of the previously mentioned UK sources easier, certainly, and maybe cheaper.

richar L.
Title: Re: Crankshaft pinion
Post by: coater87 on 08.06. 2009 17:18
 Hi Richard,

 Nope. this is all about oil pressure- I dont have a tach drive on my oil pump. Which reminds me, I dont have a speedometer either... *conf*