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Posted By: linker48x Thickness of 79 parallel port head? - 09/08/19 2:01 am
If someone has a '79 T140D or T140E parallel port head sitting on the bench, could I please ask you to measure its thickness (head gasket to rocker box surfaces) and then post the result?

I am struggling with pushrod tube leaks on my '79 T140D, which I bought in pieces. My (former, now) machinist, without asking me, told me he cut my head .060 to "flatten it" when he was doing valve guides. However, when I measured the head, it came out to be at or very near the 2.755 from the head gasket to rocker box gasket surfaces John Healy mentions in his very helpful article on curing pushrod tube leaks, at http://vintagebikemagazine.com/technical-articles/push-rod-tubes/ This makes me wonder if the head thickness of these heads differs from other splay port heads. With the standard head gasket, I only had about .040 squish, which makes me believe the head has been cut, but perhaps not by as much as I was told--more like .020 or .030 because this is the more or less the squish I ended up with early on in the life of my race engine, by using a thin .020 head gasket and thin base gasket.

The PO gave me a new JRC cylinder and pistons, and I have been told the height of the pushrod tube shoulder on those JRC cylinders can vary. If the head thickness measurement doesn't shed light, my next stop will be to remove and carefully measure the JRC cylinder and compare to the figures John put in his article for the tappet block shoulder thickness (.790-.800), and possibly to return to the stock cylinder if it is incorrect, and/or machine .020 off the tappet block, etc.

I have had this thing apart 3 times this summer trying to fix this, and I have put a .080 head gasket, and thin square section o rings in this, and it still cuts the square section o rings through, and it still leaks. I am trying to get a handle on what is going on, so if one or more of you could measure the thickness of a parallel port head, and post it, I would appreciate it. No need for other advice, a measurement is all I need. Thanks!!
Are you saying square section rings on the head side of the pushrod tube? If so, you should be using round section..But the head thickness sounds ok and assuming you have checked for burrs that might tear o rings and the tube recess in the head is correct...... it must be the tappet blocks or the tubes casing the problem...
Put the tube in place with no seals on the ends, tighten head lightly with head gasket in place..Pry the tubes up gently and see if you can measure the gap between the tube and the tappet block flange..Then do the math on the seals you have to determine crush...But I think you may have done this?
Posted By: linker48x Re: Thickness of 79 parallel port head? - 09/08/19 9:27 pm
Thanks for the post.

Nope, square section oring on bottom, of course.

Yep, did that already.

Just need the thickness of the head to figure out what my “helper” at the machine shop did, and figure out that variable, one way or the other.
I did some work on my 79 T140D later winter involving the piston to head squish clearance.. I kind of remember the head being 2.755. I just went out and checked it...not easy to do accurately on a running bike but I believe it's 2.755.....
Posted By: BikeVice Re: Thickness of 79 parallel port head? - 09/09/19 8:47 pm
My spare 1979 T140E head measures 2.780". I'm pretty sure it has never been cut.

Eric
Posted By: linker48x Re: Thickness of 79 parallel port head? - 09/10/19 6:19 pm
Thanks Hillbilly bike and Bikevice. I appreciate your effort. Hillbilly, 2.755 is the exact thickness John Healy’s article cites. Bikevice, 2.780 is .025 more than that, which may mean these parallel port heads are thicker, or an indication of normal variation, I don’t know.

My head is about .010 under 2.755, so I don’t know how to account for the machinist’s statement he cut my head .060. I’ve built a number of T140 race engines and paid a lot of attention to this, and I’ve never seen one that would allow that much to be cut off the head without getting into the valve seat or the narrow little squish area.

Anyone else have one sitting around to measure?
My measurement was done on the bike...It's a parallel port head, I don't believe it's millled so it's possible the measurement may be off slightly..
Posted By: BikeVice Re: Thickness of 79 parallel port head? - 09/11/19 12:49 am
Originally Posted by linker48x

My head is about .010 under 2.755, so I don’t know how to account for the machinist’s statement he cut my head .060. I’ve built a number of T140 race engines and paid a lot of attention to this, and I’ve never seen one that would allow that much to be cut off the head without getting into the valve seat or the narrow little squish area.


Wouldn't a 0.060" shave to pretty much remove the gasket mating flange and cut into the lower fin? I've bought a couple of used 650/750 heads at swap meets and on eBay where I couldn't measure the thickness, always avoided the ones without a pronounced gasket flange.

Eric
Posted By: MarksterTT Re: Thickness of 79 parallel port head? - 09/11/19 4:58 am
My 'D' head measures 2.783" and has been skimmed -.007" so should have started out at 2.790" or thereabouts...hope this helps...Mark
Posted By: MarksterTT Re: Thickness of 79 parallel port head? - 09/11/19 6:16 am
Just for grins, I pulled a couple of heads out from under the bed and checked them also:

New 1972 650 splayed port head measured 2.788"


Used but uncut TR7 head (year?) 2.789"


Measured with my cheapie digital calipers but should be close. Tomorrow I can go out to garage and measure a few more especially another 'D' just to confirm, I'll also measure a new '69 or '70 TR6 head just to see if they are the same through the years and perhaps use a micrometer so as to confirm what I'm getting from calipers.
Posted By: MarksterTT Re: Thickness of 79 parallel port head? - 09/11/19 9:50 pm
Pulled out the micrometer and got some more measurements:

'66 T120...2.7955" thickest head measured
'66 TR6...2.7893"
'70 TR6...2.7904"
'72 T120...2.7885"
'73 T140...2.7924"
'69 T120...2.7900"
'73 '?' TR7...2.7868" thinnest I measured

All heads checked twice on opposite sides and would vary from .0003-.0012" and no heads exhibited signs of having been surfaced
Posted By: linker48x Re: Thickness of 79 parallel port head? - 09/12/19 7:16 pm
Thanks, MarksterTT. You put some effort into this. Your results start to make sense of what is happening here, because it seems to verify a fairly large amount has been removed from my head.

The prescribed means of measuring the amount of compression of the o rings--putting the head on with all orings present, pushing down, finger tightening the head nuts, and checking the resulting clearance over the head gasket with feeler gauges or another gasket-- did not let me get reproducible results, it seemed to vary every time I did it. Thus I ended up dry assembling without orings, and measured the available motion up and down on the pushrod tube, a simple metal to metal measurement. As a result, I added a thicker head gasket and thinner square section oring, and I thought I had it right, but it still leaks, and the square section oring continues to be cut by the bottom end of the pushrod tube. I think I am going to have to spend some time on this, during the winter. The end of the riding season in Alaska is close, so this may not be much longer...
Posted By: linker48x Re: Thickness of 79 parallel port head? - 09/12/19 7:19 pm
oops.
Posted By: linker48x Re: Thickness of 79 parallel port head? - 09/12/19 7:22 pm
Originally Posted by BikeVice


Wouldn't a 0.060" shave to pretty much remove the gasket mating flange and cut into the lower fin? I've bought a couple of used 650/750 heads at swap meets and on eBay where I couldn't measure the thickness, always avoided the ones without a pronounced gasket flange.

Eric


Yes it would, which made me doubt the figure the machinist said he cut off--not cutting the head, just the "how much" part. Which is what I am trying to figure out now. What seems clear is that there is plenty of variance in the thickness of these heads, but a fair amount was cut off mine.
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