25-07-2021, 09:50 AM
An update on this.
I wanted to repair things rather than contemplate a full rebuild. I've realised that the time involved for such far outweighs that from the sourcing of matched new parts, but also teaches you things along the way, and many peoples' assistance has got me to a position where I feel that this has almost been a successful first rebuild where I've learnt a lot about tolerances. It may be that I'm posting this too early in the 'running in' process, but my gut feel is that something needs tweaking rather than just bedding in needing to take place.
I've replaced the duff piston, and balanced the conrod assemblies to within 2g each (just the entire units, not balancing each end) and reconnected everything on the crank with some Philidas nuts after slightly scraping/sanding the shells in to allow the getting-rid-of paper shimming, the cause of one journal being loose prior to dismantling. I changed the head to a LC one, replaced the valve guides and reamed them with a new reamer. Cleaned the valves up, checked the seats and reassembled everything, discarding the worst of the rings but accepting a far wider tolerance than 6 thou - some in the second row are more like 20. (The discards included gaps of 1", 1/2" and a couple of 40 thou or so!)
The engine runs well and starts fine, but is only 10 miles into being re-assembled. It does presently breathe worse than before, through front piece, pinhole in filler cap, and the added breather pipe.
After 10 miles, did a compression test with throttle open but when engine was cold - 75/105/105/100. (Low Compression head)
This suggests to me that the tolerances on the pistons rings are fine as my treatment of no 1 piston was likely the same as the others. (I just inserted the pistons in as well as I could with fingertips from below, going with the strategy of letting them space themselves)
I'm planning on
1. checking tappets on 1 and 2, and if no issues there...
2. lifting head to check valve seat on exhaust port 1
...before contemplating taking piston 1 out.
Are there any other observations I should add and check, please? I'm presuming that with the valve guides done, at least that removes them from blame and concentrates things elsewhere. Valve seat 1 had the most attention, and I did use some coarse grinding paste to get to 'no daylight' viewable through from the underside.
I wanted to repair things rather than contemplate a full rebuild. I've realised that the time involved for such far outweighs that from the sourcing of matched new parts, but also teaches you things along the way, and many peoples' assistance has got me to a position where I feel that this has almost been a successful first rebuild where I've learnt a lot about tolerances. It may be that I'm posting this too early in the 'running in' process, but my gut feel is that something needs tweaking rather than just bedding in needing to take place.
I've replaced the duff piston, and balanced the conrod assemblies to within 2g each (just the entire units, not balancing each end) and reconnected everything on the crank with some Philidas nuts after slightly scraping/sanding the shells in to allow the getting-rid-of paper shimming, the cause of one journal being loose prior to dismantling. I changed the head to a LC one, replaced the valve guides and reamed them with a new reamer. Cleaned the valves up, checked the seats and reassembled everything, discarding the worst of the rings but accepting a far wider tolerance than 6 thou - some in the second row are more like 20. (The discards included gaps of 1", 1/2" and a couple of 40 thou or so!)
The engine runs well and starts fine, but is only 10 miles into being re-assembled. It does presently breathe worse than before, through front piece, pinhole in filler cap, and the added breather pipe.
After 10 miles, did a compression test with throttle open but when engine was cold - 75/105/105/100. (Low Compression head)
This suggests to me that the tolerances on the pistons rings are fine as my treatment of no 1 piston was likely the same as the others. (I just inserted the pistons in as well as I could with fingertips from below, going with the strategy of letting them space themselves)
I'm planning on
1. checking tappets on 1 and 2, and if no issues there...
2. lifting head to check valve seat on exhaust port 1
...before contemplating taking piston 1 out.
Are there any other observations I should add and check, please? I'm presuming that with the valve guides done, at least that removes them from blame and concentrates things elsewhere. Valve seat 1 had the most attention, and I did use some coarse grinding paste to get to 'no daylight' viewable through from the underside.