What does the "Plug - Blind, Camshaft" do exactly?

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helpIamaparrot
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What does the "Plug - Blind, Camshaft" do exactly?

Post by helpIamaparrot »

Hey all, new owner and new to the forum. I have a U20-swapped 1600 that threw a timing chain some time ago and was parked, which is when I bought it. While digging around in there to get it fixed, noticed that I was missing the plug that threads into the center of the camshaft sprocket. Not a huge surprise since when the chain threw, it thrashed around quite a bit and sheared the heads off of several bolts and mangled the upper chain guide and tensioners and generally made a fine mess of things. However, as I'm going to order replacement parts I can't find this part listed anywhere except on this diagram as #5. It's an M6 thread pitch, but what does it do? Is it necessary? Should I just get a little M6 plug and put it in there?

Also second question: I keep reading a lot about shimming the tensioner plungers and the cam sprocket to keep everything in the same plane and tight even while oil pressure is low. How can you tell if you need to shim your cam sprocket? I'm trying to avoid whatever caused the motor to throw the chain in the first place.
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Gregs672000
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Re: What does the "Plug - Blind, Camshaft" do exactly?

Post by Gregs672000 »

Welcome to the addiction! Sorry to hear the motor suffered the dreaded "evil L" destruction... your description should remind every U20 owner of what can happen if the issue is not addressed. Now to your question... the fitting there is to allow you to bolt the cam gear in place to the Evil L to allow the head or cam to be removed without having to support the timing chain. Nice idea, and it works well, except that over time the chain starts to strike the underside of the L until it fractures and destroys your engine. Mine is cut off for that reason, but if one has a new guide and shims the tensioner it should work safely as designed. Regarding shims (there are kits, see vendors, or find some (3-5) suitable nylon washers that slide cleanly over the plunger shaft) the idea is to shim the tensioner out to where it has about an 1/8 - 1/4 inch of travel to keep the chain tight until oil pressure takes over... that's the danger point and typically where the strikes occur. Make sure you have a good gasket for the tensioner and that you don't cover up the oil feed holes. I made my own thin paper gaskets if you don't have one. ALL upper tensioners should be shimmed.

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Greg Burrows
'67 2000 #588
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Re: What does the "Plug - Blind, Camshaft" do exactly?

Post by fairladyproducts.com »

Each camshaft for the U-20 has a brass plug in each end that is there to close off the centerbore made when it was manufactured. Plugs may be removed when camshafts are reground so that debris can be removed. Sometimes the brass plugs are replaced with small pipe plugs.

Plugs do not usually fall out. You should be able to see the front plug after you remove the cam sprocket.

Stan
helpIamaparrot
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Re: What does the "Plug - Blind, Camshaft" do exactly?

Post by helpIamaparrot »

Thanks for the replies! So if the center bore is there to keep the sprocket and chain in place while the cam is removed, what does the part labeled as #4 "Screw - Camshaft Gear" do? It looks like a countersunk screw with a star washer behind it but doesn't seem to actually fasten to anything.

Would you recommend cutting off the top of the chain guide? Its a nice feature but I'd rather have peace of mind knowing this won't happen again over the convenience of having to retime the engine if I need to take the head off.
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spyder
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Re: What does the "Plug - Blind, Camshaft" do exactly?

Post by spyder »

"the part labeled as #4 "Screw - Camshaft Gear"

Is an index pin to align the gear to the cam flange.
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Gregs672000
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Re: What does the "Plug - Blind, Camshaft" do exactly?

Post by Gregs672000 »

Are the cam gear holes Slotted? If so, it may be an adjustable cam gear. The pin is nice to have, but not required. People remove the pin to allow the gear to advance or retard if the holes are slotted. Regarding the L, I'd check the underside of the L for chain strikes. If it's OK, run it. Otherwise, yes you can carefully cut it off, but from then on you will be using some method to hold the chain up and secure so it does not move a tooth if you ever need to pull the head (like an L-series engine). I use a wood dowel.
Greg Burrows
'67 2000 #588
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