What's going on with my valve clearances? (sanity check)

PostPost by: The Veg » Sun May 31, 2020 2:18 am

Just a quick update, my local expert Bob Wagner got his shop moved and I was finally able to have him look at the head and valvetrain. The visit was encouraging; he saw no major issues and gave me some useful advice about valve clearances. The idea put forth earlier in this discussion that something is interfering with some of the clearances seems to have merit: Bob spotted something I hadn't, that the ends of the valve-stems have been ground, which leaves less room for the 'top hat' type shims' edges to hang down, which may have thrown off some of my measurements. I have no idea why the stems had been ground (last head-work was all done during a PO's time), maybe creating a little more room for clearance? Anyway, pay attention to that, turn the shafts more than I'd been turning them, double-check other potential interferences, etc., and expect some time and tedium to get them right but then not worry about it too much once I do get them right. I left the head with him to install a Helicoil in the hole where the bolt goes through the front cover on the exhaust side as it looked a little rough. Should get it back in a week I'm guessing. I'm looking forward to getting it back together and right again.
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PostPost by: rgh0 » Sun May 31, 2020 3:09 am

Top hat style shims come in a limited number of thicknesses. They normally need grinding to get the thickness need for the correct clearance and this is not easy to do given their size. Potentially you're DPO ground the valve stems instead to get the desired valve clearance which would be easier to do, but could result in the shims hitting the top of the collets or the retainer

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PostPost by: alan.barker » Sun May 31, 2020 11:29 am

I had that problem on my first +2 . The owner before had ground the ends of the Valve Stems a right Banker.
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PostPost by: The Veg » Sat Jun 06, 2020 5:03 pm

Another update:

I got the head back from Bob, who remains encouraging about it. After cleaning up the hole that I thought had damaged threads, he decided that it was OK and didn't need an insert. He did also observe that the valves seats, especially on the exhaust side, are cut a little too deeply, leaving less room for adjustment as they wear. I wonder if this is why the ends of the valve stems were ground. He thought it should be okay for now but if it becomes a problem later I can put in some larger valves.

I decided to adjust the valves while the head was still off, paying special attention to the fit of the shims and any interferances. It went well until I got a bit careless (unintentionally of course!) with the torque on the cap-nuts and broke off a stud! D'OH! It appeared to be the oldest of the tall ones, possibly the last original one, so I suppose its time had come- but of course it boke off below the surface, at the top of the threads in the head. This means I need to extract it but I've never done well with the tapered reverse-thread type of extractors, so any advice from those of you who've done this before?
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PostPost by: Foxie » Sat Jun 06, 2020 6:13 pm

The Veg wrote:Another update:


I decided to adjust the valves while the head was still off, paying special attention to the fit of the shims and any interferances. It went well until I got a bit careless (unintentionally of course!) with the torque on the cap-nuts and broke off a stud! D'OH! It appeared to be the oldest of the tall ones, possibly the last original one, so I suppose its time had come- but of course it boke off below the surface, at the top of the threads in the head. This means I need to extract it but I've never done well with the tapered reverse-thread type of extractors, so any advice from those of you who've done this before?


I have just removed 4 sheared bolts, rusted in, from a 1988 Nissan Patrol chassis. I got a set of tapered extractors, but didn't need to use them.

I got a set of left-hand drill bits. I carefully centre-punched the stumps, and started drilling them out, starting with the smallest bit. They all came out before I reached the nominal diameter.

With steel studs in aluminium I'd say you might have to be a bit more careful !

:)
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PostPost by: alan.barker » Sat Jun 06, 2020 6:38 pm

Only center drill using a Pillar Drilling machine. I would also make a drilling plate.
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PostPost by: mikealdren » Sun Jun 07, 2020 7:42 am

If you use a centre drill to start with (in a pillar drill), it's much easier to centre the hole. Sorry Alan, just read your reply!!!
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PostPost by: The Veg » Tue Jun 09, 2020 2:55 am

Not wanting to risk damaging the head, I took it back to Bob and he got it out in about two minutes. He basically welded a 'handle' onto the broken stud and twisted it out easily. I removed several others and saw that they were fairly stretched so I've ordered replacements. Of course I've had to go on the road again this week so I'll get back to it probably Friday. I am VERY much looking forward to getting the head finally done and back on.
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PostPost by: 2cams70 » Tue Jun 09, 2020 4:00 am

Do yourself a favour and buy a quality 0-25 Nm torque wrench. One of the best investments you'll ever make!
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PostPost by: englishmaninwales » Tue Jun 09, 2020 8:38 am

2cams70 wrote:Do yourself a favour and buy a quality 0-25 Nm torque wrench. One of the best investments you'll ever make!

+1
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PostPost by: The Veg » Fri Jul 03, 2020 1:16 am

Update: after going through the learning-curve with some of the subtleties of eliminating interferences, going through replacing a bunch of the cap-studs, trial and error with shims, etc., I've finally got the clearances SORTED and the head should be going back on this weekend.
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PostPost by: rgh0 » Fri Jul 03, 2020 2:27 am

It will be much easier and quicker the next time you have to do it :lol:

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PostPost by: nmauduit » Fri Jul 03, 2020 7:48 am

The Veg wrote:Update: after going through the learning-curve with some of the subtleties of eliminating interferences, going through replacing a bunch of the cap-studs, trial and error with shims, etc., I've finally got the clearances SORTED and the head should be going back on this weekend.


you may want to check the valve clearances again after a couple heat cycles and the head retorqued
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PostPost by: alan.barker » Fri Jul 03, 2020 9:03 am

When i have removed the Head on a Twink to do work i have adjusted Shims on the Bench.
After i have fitted the Head i have never checked Valve clearances. I have never retorqued a Head.
Maybe i have been lucky over the Years.
I have always used a standard Head Gasket.
I'm sure in competition it's different.
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PostPost by: rgh0 » Fri Jul 03, 2020 10:26 am

alan.barker wrote:When i have removed the Head on a Twink to do work i have adjusted Shims on the Bench.
After i have fitted the Head i have never checked Valve clearances. I have never retorqued a Head.
Maybe i have been lucky over the Years.
I have always used a standard Head Gasket.
I'm sure in competition it's different.
Alan


I generally find clearances change a thou or two after bolting down the head. I use fibre head gaskets and these are softer than the original copper which may contribute to this. They also definitely need re torquing but also seal better for highly stressed engines.

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