Author Topic: engine building tribulations  (Read 540 times)

Offline jachenbach

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engine building tribulations
« on: 30.01. 2015 01:04 »
Got the gasket set and sludge trap plugs for the RGS Spitfire engine. Thought it would be just a matter of assembling but........ When I took it apart, one piston was badly seized, but no worry, have a fresh cylinder/pistons waiting to go on.
Rods turned on the crank nice and smooth with the least bit of side play and no discernible vertical play. Getting them off the crank for sludge trap/oil passage cleaning was a bit of a fight, but crank journals/big end bearings all looked good. Before removing the rods from the crank I marked them "L" and "R" with a felt tip pen (I know, drilled rod on the left, but a big black letter as a reminder couldn't hurt).
  So this afternoon I install sludge trap and plugs, pick up the rod marked "L" and lo and behold, no oil passage. The one marked "R" had it. Okay, must have marked them wrong. Installed the correct rod on the left journal. No vertical play, but quite a bit of sideways rocking (not sideplay). Put the other rod on the right side. Tough getting the rod cap on, had to tap it with a plastic mallet and it started binding before I even got it snug. What the hell??????
  Took them both back off and for the hell of it put them on the wrong journals. Right side binding and left not quite right either. Frustration setting in. Both back off and measured the journals. Nicely matched and no measureable out-of round with a caliper. I'll recheck with a mic tomorrow. Assembled rods/bearings/caps off the crank and again measuring with calipers, right one seems out of round. Put it all back on the shelf and beadblasted some Triumph cases instead. (oh sorry, I used the "T" word)
   I have what appears to be a set of reconditioned rods with brand new bearings and bolts. Not labeled, but assembled as above they seem to be .020" smaller than my crank journals, so I suppose I could have the crank ground but that seems a waste of a lot of crank life. Wondering if I could have damaged the rods. Or maybe the bearing shells. Think I'll leave it on the shelf and work on something else while I think about it. Trying to do a low budget build but it's got to be right. Sometimes those two things aren't compatible.

Online bsa-bill

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Re: engine building tribulations
« Reply #1 on: 30.01. 2015 09:04 »
in an ideal world it shouldn't matter but any chance you somehow swapped the caps, as  said it shouldn't matter
All the best - Bill
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Offline The Artful Bodger

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Re: engine building tribulations
« Reply #2 on: 30.01. 2015 10:25 »
The caps must be on the rods they came off of and must be the right way round, especially if they've been re-claimed at any time from ovality. The way this is done is to reduce the mating surface between the cap and rod, give them a tap to close the sides up, then hone the big end hole round again. If the cap is either not from that rod or put on the wrong way round the two halves of the hole will be offset.
  By putting the caps on the rods without the bearings in place you should be able to tell if there's any misalignment. Out of old habit, before removing any bearings caps (mains or big ends) I always center punch both halves with the correct number of dots for that cylinder, main bearing position, towards the front of the engine. This way no matter how dozy I am when I put it back together I know everything is in the right place, in the correct order and facing the right way.
  Also it saves any confusion if someone in the past has incorrectly assembled it (as in this case the oil hole rod possibly being on the wrong journal), at least I know for sure how it was before I disturbed anything.

Offline jachenbach

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Re: engine building tribulations
« Reply #3 on: 30.01. 2015 17:01 »
Good idea. I didn't think about the caps being backwards and didn't mark them because they have numbers stamped in them, so matching to the correct rod isn't a problem. Backwards seems a good possibility, as the right side bearing edges are about 1/8" from lining up when assembled. Should have paid closer attention. I've also noticed that when assembled with the numbers on the same side, the notches to orient the bearings are on the same side of rod and cap. Seems to me they should be on opposite sides. Shouldn't start this sort of thing when I'm tired.

Offline muskrat

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Re: engine building tribulations
« Reply #4 on: 02.02. 2015 09:31 »
Numbers should be on the same side and when on the crank, facing the same direction.
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