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#60
by
RadoTD
on 11 Nov, 2010 21:53
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I have an OBD1 ABA cam lying around if you need one 
-Owen
Mmmmkay, so I just ran down and looked at it... it looks like the cam would actually fit in the head and even if it didn't, that's not a machined surface or weak point... some "clearancing" with a die grinder would fix that.
.008" from the HG, plus there is more than .040" between the valve face and the valve seat... I wonder how much would actually have to be removed to clear. I suppose the only way to know for sure is to put one in a head and try it.
You suck, Owen!
*edit - does anyone know if that would lower dynamic compression, and does dynamic compression affect cold starting issues? I assume it would because you're not compressing the cylinder right from the bottom.
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#61
by
truckinwagen
on 11 Nov, 2010 22:16
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the ABA cam still has negative overlap, so dynamic compression should not be too much of an issue.
from the measuring I did the ABA is very similar to the diesel cam, except lift.
most of the duration differences are on the BDC end of the stroke, so there should not be too much issue with valves hitting the pistons.
of course the only way to know for sure is to slap one in a head and turn the motor over by hand to see...
-Owen
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#62
by
RadoTD
on 11 Nov, 2010 22:34
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from the measuring I did the ABA is very similar to the diesel cam, except lift.
Oh crap, looks like I might be finding a way to get an ABA cam mounted now...
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#63
by
truckinwagen
on 11 Nov, 2010 22:41
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physically, the only thing needed to do to install a gasser cam in a diesel is an adapter to go from the keyway end of a gasser cam(just like the end of an intermediate shaft) to the diesel taper.
but as you have access to a lathe, that should not be an issue...
-Owen
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#64
by
RadoTD
on 11 Nov, 2010 23:00
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Interesting.. how much for shipping down here? I can pm you my address again if you need it.
They only way I'll run it is if I actually clear without facing my valves down though. If I face my valves first, I have no way of knowing how much clearance there is. At least if it's clear cold with stock valves, 30 thou taken off the face of the valve, I know there's 30 thou of clearance!
Still not too sure about this, I really don't want to end up destroying my engine before I really get it going for something silly like this
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#65
by
rabbitman
on 11 Nov, 2010 23:06
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They only way I'll run it is if I actually clear without facing my valves down though. If I face my valves first, I have no way of knowing how much clearance there is. At least if it's clear cold with stock valves, 30 thou taken off the face of the valve, I know there's 30 thou of clearance!
You can put the crank at TDC measure valve clearance and then push the valve down until it hit's the piston then measure again. Unless you have hydro lifters that'll mess with the readings.
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#66
by
truckinwagen
on 11 Nov, 2010 23:07
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well, for the price of shipping the cam is yours, it is just taking up space at my place right now...
your address would be great to figure out the shipping cost.
the other thing you can do to check actual clearance is put some clay on the piston tops where the valves would contact, then after you turn the engine over you can pull the head and check the thickness of the squished clay.
that way you can be sure of the actual clearances involved.
-Owen
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#67
by
RadoTD
on 11 Nov, 2010 23:13
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Hmm, both good ideas. Any idea how much clearance I should hope for? Also, Rabbitman's idea might be tough, because I think it's a few degrees before and after TDC that it would be most likely to contact. Not sure on that though
For the purpose of testing it, would I just clamp the old head gasket instead of crushing a new one?
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#68
by
truckinwagen
on 11 Nov, 2010 23:32
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for testing the old head gasket would be fine.
and the nice thing about the clay trick is it shows you the absolute closest the valve would ever get, even if you dont know when that is.
-Owen
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#69
by
745 turbogreasel
on 11 Nov, 2010 23:58
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for testing the old head gasket would be fine.
and the nice thing about the clay trick is it shows you the absolute closest the valve would ever get, even if you dont know when that is.
-Owen
Or almost...heat expansion, rod stretch at RPM, and timing belt elasticity remain a mystery.
ED; Cam twist too.
Are the forces really that crazy on them?
The valve seat is the thinnest part and takes the largest amount of force, but I can easily take enough material out without going near the valve seat. If I were to take a 3/4" drill bit for the intake valve and 5/8" bit for the exhaust, then drill those into the valve just until the tapered head is all the way in, that'll give me right around what I need. A 19mm diameter cone at 22.5deg (135deg drill bit) isn't a whole lot taken out of the valve in a non critical area. I also don't have to pay a machine shop for that 
Drilling the valves like that would give me about 1cc/cyl and a 3 notch instead of 1 notch gives another cc, bringing my CR to just over 20:1, with the option of putting the right head gasket back on to bring my compression half the way back.
Not a huge effect on squish/quench (something I'll need to do some reading on to understand better!) while bringing my CR right where I want it
The force on the seat is spread over a huge(relatively) area, but it all comes through the neck. ever seen a valve fail in such a way as to shed a 'skirt'?
If they hit something one side might fall off, but if the valve just fails in operation, the head drops off the stem, and falls into the engine nomnomnomBOOM!
One of these valves is sodium filled, and one is not...Feeling lucky with that drill ?
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#70
by
truckinwagen
on 12 Nov, 2010 00:00
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well, yes, all that too.
but it will show static clearance, so then all you have to do is decide what you think is appropriate clearance to account for the other variables.
-Owen
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#71
by
RadoTD
on 12 Nov, 2010 07:53
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The force on the seat is spread over a huge(relatively) area, but it all comes through the neck. ever seen a valve fail in such a way as to shed a 'skirt'?
If they hit something one side might fall off, but if the valve just fails in operation, the head drops off the stem, and falls into the engine nomnomnomBOOM!
Do you mean to say they fail like this?
I won't undercut them, so where I would be taking material from wouldn't affect that at all.
Any way to find out if they are sodium filled? They're original OEM valves.
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#72
by
lord_verminaard
on 12 Nov, 2010 10:56
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Re: Gasser cam. How are you going to time the engine? The slot in the back of the diesel cam is not there on the Gasser one. Would be a bit of a *** to try and find exact TDC on a cam with a different profile than the stock one and cut the slot at just the right place. I wouldn't know any other way to time the cam when the difference of a degree or so is enough to lunch the head.
Brendan
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#73
by
RadoTD
on 12 Nov, 2010 19:35
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Re: Gasser cam. How are you going to time the engine?
That is a very good point. I threw running an ABA cam out there kind of as a joke, then it seemed plausible but I think it's just too sketchy for me to be running right now. Maybe if this were a second car...
I still want to look into machining my valves. I think for the work it'll take, the benefits will be worth it.
I called my machine shop and asked them about it, they said that only the stem was filled with sodium and they were fine to machine. The old 1.8L mk2 gassers also had sodium valves, so I'm going to get one of those, break the stem off, carefully dispose of the sodium (throw it in a bucket of water while wearing safety glasses) and then cut the valve apart to see how far down the stem the vein runs. Then I'll know if it's safe to machine them out on a lathe!
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#74
by
RadoTD
on 13 Nov, 2010 19:15
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Okay, so I've decided to leave the valves alone. I'll get it running for now, maybe go bigger someday later. The picture below made me nervous, I didn't realize how far down the sodium went. That's not a VW valve, but I would expect mine to look the same.
Maybe someday later I'll give it a shot. I should really get this car back together for now though. Thicker head gasket will be the extent of my compression reduction for now.
Tomorrow's job... port the head *evil grin*