Big End Shells

[1949BSA]

Hi,

I have to look for new big end shells for a 1950 A7 Long stroke engine.

I do not know, when there are changes of the shell dimensions for the condos / big ends.

Hope someone can give me informations.

Michael

[Swarfcut]

 The Longstroke crankshaft for your model year uses the same bearing shells as the small journal crankshaft used on the A10 and similar A7.

 Service Sheet 207 gives big end journal regrind dimensions for A7 engines from XA7601 onwards. Standard size big end journal is 1.4600"/1.4595", as detailed in my good old Glacier Bearing Catalogue. Haynes says 1.4595"-1.4660, which looks to be a Typo!.*

   As always, the crank end plugs must be removed and the oilway "sludge trap" cleared of carbonised oil and accumulated muck.

 The big end eye of your steel conrods can be checked, bore is 1.6055/1.6060, the same size as on the alloy rods used on later engines.

 Glacier bearing reference is B2024, Vandervell  is VP 60, both trusted manufacturers back then, and were available in  -10, -20, -30, & -40 thou undersizes. New old stock of Glacier and Vandervell sometimes shows up, Hepolite brand these days is owned by Wassell, and nothing to do with the original company.

 Plenty to read about crankshaft grinding already on the Forum, along with pictures and stories of when things go wrong!

 Swarfy.

 * 1973 Edition, Page 15, Crankpin track diameter.

 

[KiwiGF]

Some info…

https://www.a7a10.net/forum/index.php?topic=5028.0

[1949BSA]

Thanks for the informations.
I was able to find out, there are several sizes of "narrow shells" available on the continent.

The engine is now out of the frame . Seems so only the left side big end has sized.
I have to look for the damage of the big end pin. My hope is to, it is good enough to polish it and get use a new pair of shells (on both big ends).
Next I have to manage is to get of the crankshaft pinion from the crank stub, before I can split the cases. I have not the fitting extractor.

Michael

[limeyrob]

Do you mean the drive side bearing or the timing side gear under the left hand thread?
For the bearing you need a very sharp bearing extractor that you can clamp under the edge.
For the pinion it has two grooves in the tapered part.  A thin 2 leg puller will just fit in these (well after you have ground off 90% )

[Swarfcut]

 Rob makes it sound easy, but you may have problems. The small timing pinion usually has two grooves, as Rob says, but early engines are sometimes found without the grooves for a puller...I have one to hand. If this is the case simply pull from behind the pinion, a home made 2 leg extractor is the usual way. Protect the end of the crankshaft and its left hand thread, these are relatively soft and damage easily. Usually not on very tight, the secret is to make sure the legs can not slip off and the pull is in line with the crank centre axis.

 Your engine will have a ball race bearing on the drive side, in most cases the crankshaft will tap through the bearing. If not, heat the crankcase around the bearing, the case will expand and release the bearing still attached to the crank.

 Service Sheet 206 gives detail if dismantling procedure. Sheet 208 tells how to put it back together.

 Even if you are lucky to have minor pick up on the journal, it is essential the crankshaft is cleared as mentioned above, otherwise the same seizure problem will happen the first time you start it.

 There is no need to remove the camshaft drive gear. The cases will come apart leaving the cam in the timing side case.

 Swarfy.

[limeyrob]

Any "sounding easy" was entirely unintentional . If you don't have the grooves in the pinion and use a 2 leg puller under the gear (there's very little space) clamp the legs of the puller with a small G clamp to stop them slipping up over the gear teeth.  Its a good idea to do this even if the puller is in the grooves as there is very little for it to grip.
Measure the end-float NOW, before you split the cases.  Having a starting figure can save a lot of hassle when you come to set it on re-assembly.

[1949BSA]

Scarify and Limeyrob,

many thanks for the informations. With a "home made" extractor I had success to get of the drive side Crank pinion. Tomorrow I will split the crank case and have a look to the big ends.

Michael

[1949BSA]

Today I had a look to the sized drive side crank pin.
I make up my mind, what to do.
It is now -20 tho undersize.
May be I can save the surface???


Michael

[limeyrob]

Put some oil on it, very fine emery and a shoelace wrapped round it then pull back and forward. Just do a bit then measure.  Its is under-size then it has to be a re-grind.  A crank grind / shells should last 20-30,000 miles or more so there's no need to worry about engine life.

[chaterlea25]

Hi All
Michael,
While you have the engine apart, it is also essential to check for wear on the timing side bush and crank end journal
On the long stroke also check the camshaft and followers for wear

John

[limeyrob]

I recently rebuilt my engine and bought the un-machined timing side bush. Then I got the crank ground to just clean it up and had the bush machined to fit.  The crank was -20 so it ended up -25 which gave me one more chance and also meant the machine shop could get the bearing fit just right.

[1949BSA]

I have managed to clean off the seized white metal from the crank pin and the pin has still his original   - 0.002 pin did and a useable surface.
New shells are now fitted and also the drive side crankshaft bearing (RMS 9) is new.
I add some photos.

Michael