Hi Tom,
Yes, I did the 'droop' test on the chains, and took a couple pictures. The
old one physically looked fine, but it bent down in an arc.
You and Bruce have a nice trick with the countersinking. I found a lot of play
with the big chain guide, and it drove me nuts trying to center it on the holes.
Countersinks would solve that problem; wish I knew that when it was a bare
block. One of the old bolts had half its head scaped off by the chain slapping
around. Due to worn gears and worn chains. The cylinder head had nothing to do
with it, as it had never been milled. This is a blown U20 engine I inherited
about 25 years ago.
I'll re-orient the lower tensioner so the rounded edge points to the crankshaft.
Now it makes sense after visualizing the chain moving in a CW fashion. The
trailing edge should be straight, otherwise the chain could drag a chunk off a
rounded trailing edge. You've got access to computer modeling? Wow! The
'back-slapping' of the lower chain when letting off high rpm's ocurred to me. So
I decided to leave off the lower chain guide. How much stress can it take off
the jackshaft, if it's going to snap off the guide? Unless that's the primary
function of the guide, to fail first before the jackshaft does. Hmmmn. Doesn't
seem likely, because the jackshaft looks a lot more rugged than the guide so
they would have made the guide a lot stronger if this was it's function. Oh
well, I'll take my chances with it off, as I figure it would break anyway.
Fred - So.SF, CA
BADROC
'66 waiting for the U20
'70 1600 Blondee
'68 2000 frame-off
_________________________ Reply Separator __________________________
>Subject: Re: timing
>Author: walter@omni.sps.mot.com (Thomas Walter)
>Date: 8/19/99 8:09 AM
>
<snip>
>Also with the chain off, and held horizontally, I can tell the difference
>in the amount of chain wear by how far it 'droops'. When compared next
>to a new chain you'll realize the amount of wear to the links.
>
<snip>
>One other trick, thanks to Bruce Schluderman, is to replace the two 6 mm
>hex head bolts with counter sink screws for a flush installation.
>Usually I like installing allen key bolts, as the chain (with age) can
>brush up against the bolt head. Flush screw allows for a cleaner
>installation, but does require machining the guide AND BLOCK with a 82
>degree counter sink.
>Amount of metal removed on the block is only 0.020" at the entry of the hole,
>so it is something I only recommend doing prior with a bare block.
>
<snip>
>My lower tensioner is the same as you describe. Personally the rounded edge
>should be towards the "incoming chain" which means pointed down towards
>the crank!
>
>I am still down right baffled by that lower chain guide. I think mentioned
>asking a mechanical engineering friend to make a computer model of the chains
>and jackshaft and camshaft. The lower chain guide can ONLY function as a
>step of high rpms being let off, and the chain 'back slapping' that
>guide. Odd thing is with time, and VERY WORN OUT chains, it will break
>that lower guide off. Basically it serves no purpose other than to fail
>with worn out chains! Odd. No never got the full model made, but maybe
>I'll get LEARN
>how to use the full engineering package of Matlab & MatrixX someday to
>play with this some more. Dynamic model is pretty interesting with a
>camshaft.
>Fun thing with my job, as I get paid to go off an think about these things. ;-)
>
>Cheers,
>
>Tom Walter '67 2000
>Austin, TX '68 2000
>
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