Author Topic: A sad case  (Read 1051 times)

Offline olev

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A sad case
« on: 12.09. 2010 09:11 »
Gday All,

I?ve finally collected the gear to build a new bottom end for the A7 plunger and have run into strife.
The original cases were welded up, ?sprung? and generally stuffed. 
I managed to get another set using extortion, cash and some pleading.
The cases are stamped with the same batch number so they are probably a set.
The problem is that with the crankcase locating dowel fitted, nothing else lines up.
The holes for the two studs near the locating dowel won?t line up and can?t be fitted.
The crankcases at the gearbox and sump don?t line up. The suspicion is this engine was originally built without the dowel pin.
If the dowel is taken out, and all the bolts tightened up, things line up reasonably well.
How does this sound for a fix?

1. Loosely fit all the crankcase bolts without the dowel.
2. Bolt on the gearbox and sump to align the cases then tighten everything up.
3. Pin the cases somehow ??
4. Get a new timing bush line bored.
5. Get the deck machined parallel to the crank.
6. Get new camshaft bushes line bored.

Before anyone suggests I hand it over to an expert, been there done that.
All the work was done with the dowel in and the adjacent studs out.
With a new timing side bush, the crank spun sweetly but as the cam was bent 2 thou from the nitriding it was tight in one spot.
After the cam was straightened, it was tight everywhere. On removing the dowel, adjusting the cases and fitting the missing studs, it slopped and banged about with huge clearance. The bushes had been reamed to death. But the crank wouldn?t spin sweetly.
It?s difficult to blame the machinist as I handed the cases over with the dowel in.
Before he has another go I'd like to find any hints that might help us.

This brings up another question.
With new bushes (that haven?t been reamed), the camshaft spins freely in each crankcase half but tightens up when the cases are fitted together. It can be turned easily with a spanner but not by hand. Does a straight ream of the individual bushes fix this? Does a line bore or line ream fix it. Should I fit a Triumph motor?

Offline Mark Parker

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Re: A sad case
« Reply #1 on: 12.09. 2010 10:12 »
So have you now fitted new cam bushes? And the cam spinns free in each individual case? If you ream them individually they will be opened up and possibly spin ok but will be opened up, I'd tend to bolt it up and spin it so the cam leaves a mark on the bush then maybe try to relieve that area till it spinns then line the cases to that and machine everything else again minus the dowl, you could possibly find a case bolt hole that could be drilled bigger and have a hollow dowl knocked in that,  then have the bolt pass through it (some Cyl heads are dowled like that). Theoretically the crank bore should remain true because of the case spigot, if it varies I'd be checking that there isn't something on the surface where the case meets that holds it a little unsquare, then again if the bush was machined not lined up with the case spigot it may not be right rotated a little. The main bush can be reamed with a ream fitted with a pilot into the Drive side case with it assembled.
Had a nice A10 once, :( now only have the power egg child A65 :(

Offline chaterlea25

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Re: A sad case
« Reply #2 on: 12.09. 2010 13:54 »
HI Olev,
Sad case(s) indeed!!!!
I would think that you need to align the cases /mating faces as best you can then redo the dowel (oversize??)
From other postings the spigot between the cases cannot be relied on to align the main bearing housings
You need to start at the D/S main bearing housing and work from there,
Probably another new main bush required, and new cam bushes as well
You may still have to machine the cylinder base parallel to the mains , It needs to be checked anyway!!

The only other hope is to find yet another set of cases?????

John O R
1961 Super Rocket
1963 RGS (ongoing)

Online RichardL

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Re: A sad case
« Reply #3 on: 12.09. 2010 16:17 »

Sorry that I am unable to give learned technical opinion on your problem, but I think too much depends on the alignment of the cases to leave the fix to any form of bodging. (Same goes for the sump plate fit in another member's recent post.) I say, follow the most rigorous and technically correct approach. I try to reserve my own bodging for less critical parts. With whatever respect is due the machinist that did the work with the dowel in, it is difficult to envision him as the best possible expert if the results are unacceptable. I recommend that you contact our member Richard (Orabanda) either through the forum or by direct email and ask him who he thinks would be the best person/shop to send your cases to in Oz. Also, his opinion on the fix would be interesting and probably useful. Richard is on the same little island with you  *smile* ;) , just a few thousand miles away. I'm sure you've read many of Richard's posts, so I'm may not be telling you anything you haven't already thought of.

Richard L.

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Offline Goldy

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Re: A sad case
« Reply #4 on: 12.09. 2010 17:32 »
I had a similar problem, and decided that the important datum was the cylinder barrel face, so I removed the dowels and bolted the cases to the barrel. I tightened the barrel bolts slightly and then the case joint bolts slightly and kept tighteneing the barrel and case bolts equally. I then worked on the alignment checks from there. All the best with it.
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Offline terryk

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Re: A sad case
« Reply #5 on: 12.09. 2010 17:44 »
Gday Olev, firstly dont put a Triumph motor in it that will only be going backwards straight off the mark.

This is only my opinion but I have thought alot about this with trying to match crankcases that didnt originally start out thier life together from the BSA factory. The main thing with crankcases is to have the cam and crank run true to the top where the barrells bolt on. So as long as the pistons and rods go up and down evenly and the cam meets its followers correctly all the other things are secondary really.
Bolt holes, dowles and sum plates can all be moved when you think about it. If the main things like the crank, cam and barrell are in the correct place then all the other things can be realigned to suit them.
If you have an old timing bush still in your cases then knock it out. Then machine up a mandrel to fit into the bare main bearing and timing bush holes.
It should go right through so it sticks out both sides and so you can get a set of vice grips on it to turn it. Make the ends of the mandrel smaller so the parts where you put the vice grips doesnt damage the bearing and bush holes when you pull it out. Make the mandrel a light fit so it turnes easily but snug, you dont want to take out any metal out of the holes so make sure you oil the holes. You dont need to turn the mandrel very much. Obviously the mandrel will have different sizes for the timing side and the drive side and it will need to be put in between the cases before bolting them together.

I would use the straight cam that you now have as a guide. Check that all the cam bushes are in properly and bolt up you cases and try to turn your cam use oil in the bushes. If it doesnt turn easily as you said loosen the case bolts then tap one case gently up or down and keep trying it until you can move the cam relatively easily. You dont want it spinning by hand otherwise the cam bushes are to worn.
Keep going with this for the cam and mandrel if you find a spot where they both turn ok then thats it. Use a milling machine and machine the top of the cases where the barells sit. Realign dowles and any bolt holes etc. Line bore your timing bush true to the drive side bearing hole and I think you would be fairly safe once this was all done. I hope this makes sense and it helps. cheers Terry
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