Oh dear, what has been done to my cylinder head...
Posted: Sun Oct 06, 2019 11:43 pmA valve and valve guide replacement on my head has turned into opening up a whole 'nother can of worms!
I dropped the head off at my machinist to have the valves and guides replaced. A couple of days later I got a call saying that one of the sleeves for the exhaust tappets (no. 2 cylinder) was very loose and had some, erm, mechanical damage where there was, let's say, uh, "carnal knowledge" between the cast iron sleeve and the camshaft lobe. There was no visible damage to the camshaft lobe but there was clear damage to the sleeve (this explains the metal grit I found in my oil pan when I stripped the rest of the engine down - never good!).
I had the bottom end of the engine apart just 20 miles ago - it is stripped down again due to me being bad at reading tolerances and reusing some pistons that should have been replaced. I do know for a fact though that there was no damage to the sleeve when I put the engine together 20 miles ago as I did a through visual inspection of the head. So now, as part of my slightly annoyed at myself "pulling out all the stops" attitude I'm also rebuilding the head at the same time. Which is how we got here.
Upon further inspection though it appears that this is even worse than it looks and I am confused. I can't eloquently put this into paragraph form, so here is a list of observations:
1. The measured OD of the cast iron sleeve is approximately .005-.007" SMALLER than what is specified for the OD (as listed both in my workshop manual and the Dave Bean catalog)
2. It appears that the side of the sleeve and the head were drilled into after the sleeve had been fitted, cutting into both at the same time, and then the hole was tapped and a small screw was installed, almost acting as a roll pin of sorts.
3. No other sleeves have any indication of looseness or movement.
4. The exhaust valve guides had been knurled previously (don't attack me - I didn't do it!), and also had excessive wear. I guess this explains why I had such awful symptoms of worn exhaust guides.
5. Each of the exhaust guides had what looked like a small chip taken off of the top of them near the side closest to the spark plugs. I have no idea what this is from but it must have been intentional because it's the exact same size and in the exact same place on all 4 of the guides.
6. There are lots of punch marks around the tops of the tappet areas in the aluminum of the head.
The best conjecture I can make is that undersized sleeves were deliberately used due to not being able to get the correct size for replacement at some point in the past but something still seems fishy. Also the cutouts in the valve guides puzzle me.
See attached pictures for details.
Thanks,
Ben
I dropped the head off at my machinist to have the valves and guides replaced. A couple of days later I got a call saying that one of the sleeves for the exhaust tappets (no. 2 cylinder) was very loose and had some, erm, mechanical damage where there was, let's say, uh, "carnal knowledge" between the cast iron sleeve and the camshaft lobe. There was no visible damage to the camshaft lobe but there was clear damage to the sleeve (this explains the metal grit I found in my oil pan when I stripped the rest of the engine down - never good!).
I had the bottom end of the engine apart just 20 miles ago - it is stripped down again due to me being bad at reading tolerances and reusing some pistons that should have been replaced. I do know for a fact though that there was no damage to the sleeve when I put the engine together 20 miles ago as I did a through visual inspection of the head. So now, as part of my slightly annoyed at myself "pulling out all the stops" attitude I'm also rebuilding the head at the same time. Which is how we got here.
Upon further inspection though it appears that this is even worse than it looks and I am confused. I can't eloquently put this into paragraph form, so here is a list of observations:
1. The measured OD of the cast iron sleeve is approximately .005-.007" SMALLER than what is specified for the OD (as listed both in my workshop manual and the Dave Bean catalog)
2. It appears that the side of the sleeve and the head were drilled into after the sleeve had been fitted, cutting into both at the same time, and then the hole was tapped and a small screw was installed, almost acting as a roll pin of sorts.
3. No other sleeves have any indication of looseness or movement.
4. The exhaust valve guides had been knurled previously (don't attack me - I didn't do it!), and also had excessive wear. I guess this explains why I had such awful symptoms of worn exhaust guides.
5. Each of the exhaust guides had what looked like a small chip taken off of the top of them near the side closest to the spark plugs. I have no idea what this is from but it must have been intentional because it's the exact same size and in the exact same place on all 4 of the guides.
6. There are lots of punch marks around the tops of the tappet areas in the aluminum of the head.
The best conjecture I can make is that undersized sleeves were deliberately used due to not being able to get the correct size for replacement at some point in the past but something still seems fishy. Also the cutouts in the valve guides puzzle me.
See attached pictures for details.
Thanks,
Ben