The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: michael snellin on 04.07. 2012 16:25

Title: Crankshaft problems !!!!!
Post by: michael snellin on 04.07. 2012 16:25
Hello, everybody i have just joined the forum, my tale of wo, started when i purchsed a box of bits for the A10 i,e.frame and all the other bits and pieces and what i did not have i had to search for what a big, big, mistake? however the problem that i have now is that when the two halves of the crankcase are joined the crank just locks up,i have had the b.ends,reground,new bearing to the drive side with 3thou shim, new bearing to the timing side,all done by engine rebuilders,can some one please tell me have i got the right crankcase, the engine case  has C A,stamped on itA7??, ,but i also have a crankcase with D A, stamped on it just wondering if i should have used that,the parts book list i think two part numbers.for both cases,last but not least not saying i am very clever, with these bikes, but i do try the best i was a project that i thought of over the coming months.any help would be very much appreciated.
Title: Re: Crankshaft problems !!!!!
Post by: Goldy on 04.07. 2012 17:01
Hi Michael welcome. the first thing to do is look along the edges of the two crankcase halves for two numbers which should be matching. This shows that the crankcases where paired together before machining.
All the best Goldy
Title: Re: Crankshaft problems !!!!!
Post by: a10gf on 04.07. 2012 19:36
Welcome, am hoping you'll get all the help you need.

Time for the detective work. Removing the shims, does it turn?
Maybe check that the driveside \timingside bearings are of the correct type, and properly seated.
Title: Re: Crankshaft problems !!!!!
Post by: muskrat on 04.07. 2012 20:18
 G'day Michael, welcome to the forum.
                                                    Ditto what Goldy & a10gf say. Does the cam shaft lock up as well? Do the stud nuts up finger tight and give the cases a LIGHT tap with hide mallet around the joint whilst rocking the shafts. You may need to twist the cases to get the barrel flange flat. Then do the nuts up 1/4 turn and do the same, tighten in a criss cross pattern. Keep doing in 1/4 turns till all done. If either shaft locks up back off the nuts till it just starts to turn and rock back and forth with a few more taps. Did it free up, yes continue, no strip back down and look for shiny spots on bushes.
Title: Re: Crankshaft problems !!!!!
Post by: duTch on 05.07. 2012 11:08
G'day Michael, where are you??,
       As the others say, and without a lot of thought(?),I would think the camshaft should not be affected by the crank end float clearance or lack of, and if either shaft(ie cases) is/are not mis-aligned, should spin spin ok even if the crank is tight?
   As Muskie(too bad 'bout the footy heh!!?) says, loosen off case studs, and if gap in cases is excessive see if you can get a feeler gauge in anywhere all around-will only be a rough indication, but if greater than the 3 thou already, maybe the timing bush flange/boss is too thick ? Someone let me know please if I got that wrong- Had a few big days at work?
 Cheers duTch
Title: Re: Crankshaft problems !!!!!
Post by: Sparky on 05.07. 2012 18:11
Are you able to put a micrometer on the timing side journal and verify that is is true and properly sized? I had my crank turned by a supposedly reputable machine shop, and found the journal was actually tapered by a few thousandths causing binding just as you describe.  Also, have any welding repairs been done to either engine case? That can lead to warping and alignment problems if the machinist didn't clamp them firmly together when align boring the timing bush.
Title: Re: Crankshaft problems !!!!!
Post by: michael snellin on 06.07. 2012 16:16
Thanks, to all the guys who helped me,with the crank problem,yes the numbers on both the cases are correct, i did remove the shim refitted the bearing, still crank locks up?? i suppose now i will rt to the engine rebuilders to see what they say i am just wondering if they lined bored it,perhaps someone would, when time pemits to explain what that acutally means.???.
Title: Re: Crankshaft problems !!!!!
Post by: Goldy on 06.07. 2012 16:56
Michael. the timing side bush is supplied with an undersized bore and after fitting it has to be opened to the correct inside diameter. Some people refer to this being reamed out but this is not quite correct because the bore not only has to be opened up, but this must be done in line with the crank case bore for the drive side bearing. the correct way is to mount the cases on the table of a vertical borer and then after correct alignment bore through the bush. all the best Goldy