U20 Broken Timing Chain - What to Expect

[Gregs672000]

Looking forward to seeing what you find!

[WHFred]

Happy Holidays!

I finally have the car in my own garage! Title Transferred!

I pulled the valve cover and inspected the cam and rockers. Nothing obviously bent or broken. See pics. I was glad to see oil covering all the parts. I did notice that at least one of the cam lobes has heavy pitting. If I can source a new cam shaft I think I'll replace it.

I removed the radiator and fan, pulled the spark plugs, and I can easily turn the motor with a socket wrench. Clearly the cam is turning and valves are opening and closing, so I have no idea what the prev owner was talking about regarding broken chain. I have a call into him to find out more.

I think next step is to pull the water pump, main pully, and timing cover and see if the marks on the gears all line up. While I'm there I'll get a close look at the tensioner. If the gears line up, I'll leave the head alone and reassemble and try and run it. If they don't line up I'll probably pull the head and see what the pistons and cylinders look like.

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[WHFred]

BTW, here are some additional pics.

What is with the additional metalwork inside the valve cover? Anyone seen this before?

This engine has just the alternator and water pump being driven off the main pully. Do I need to source an air pump?

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[redroadster]

Dang looks like it's just been put together as clean as the aluminum is on the head .
I'd try a 7psi leak down test , if it does turn over by hand 80 % leak is good
Airpump ....that's cute , right guys

[WHFred]

I'm hoping that I got lucky with this U20.

I saw a post here that linked to NGK (4922) BR6ES Spark Plugs. Can someone confirm these are correct? Current plugs in it are Bosch WR7CP.
What oil should I run ? Conventional 30 or 40wt? I'm in SoCal, so it'll be seeing some hot days with air temps > 105F.

Distributor has been converted to EI. I see the vacuum advance is disconnected and I'm guessing this is part of the EI conversion? Can someone confirm that this setup needs no vacuum hose connected?

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Thank you all for your help! I need it, and appreciate it!

[david premo]

The NGK BPR6ES-11 is what you should use since you have the match-box electronic ignition. The P is for a projected tip which will give you better performance at all RPM’s on the street and the 11 is a pre-gapped to 1.1 millimeters or .044 thousandths of an inch. The wider gap gives you more complete combustion, as it starts with a bigger spark due to the higher voltage of the electronic ignition. Nothing appears to be broken, so I highly recommend you check everything out very carefully before making a bucket of bolts out the engine. From what the previous owner is alluding to, he must have felt that something was broken or ready to break. The U-20 engine is a very good engine, but like all engines they each have weaknesses and I think you should proceed only after verifying that you don’t have a ticking bomb on your hands that’s waiting to explode. If the work is outside of your skill set, then there are some good mechanics in the LA area that would be able to check your engine out.
Dave

[jhayden]

The inside of the valve cover does not show evidence of a broken (uncommon) or thrown (very common) upper timing chain. It does show that the cover has been repaired due to overtightening (extremely common) of the cover nuts.

Your street engine still benefits from a vacuum advance regardless of ignition type. Just ensure that the vacuum hose is connected to the fitting next to the carby, not the one on the intake manifold.

Happy holidays.

Jon

[jrusso07]

I can't tell from the pic but is the evil L in place? This is part of the upper chain guide that allows you to mount the cam sprocket to it to keep the chain in position. Pull the inspection plate on the front of the head and look at the underside of the evil L. It's called that because the oil pressure tensioner may not be engaged enough at start up and the chain hits the evil L - indicating either a stretched chain or a tensioner that needs to be shimmed. This cuts into the chain guide and damages the chain.

Here is a quick video: https://www.youtube.com/watch?v=hQ0dGn3zQS8

Looks like you have a non-smog head (no place for the air injectors to screw in) - so no air pump (nobody runs them anyway)

SU carbs had a vacuum advance, Solex carbs don't.

[WHFred]

Here is a good pic of the evil L. It shows a groove maybe 1/16" deep indicating the chain has made contact with it. It appears that the tensioner is not shimmed.

I have no idea if the chain that is on the car now caused this groove, or if this was old damage from before the last rebuild. The chain is not nearly as slack as in the video you linked to. In order for me to get the chain to touch the bottom of the L I need to push pretty hard, but I can barely make it touch. I assume that when the tensioner is setup correctly there is no way for the chain to touch the L?

Also, I see what looks like a screw or bolt missing from top of the chain guide. Is there supposed to be a fastener in that hole?

Let me know your recommendations on replacing the chain.

Thanks!

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[WHFred]

Also, what is the recommended fix for the tensioner? I see some guys shimming with washers, which seems very unforgiving. Others put in a stiffer spring which seems like it would help resolve the issue while still allowing movement of the tensioner pad.

[theunz]

First off there should be a short countersunk Phillips head screw in that hole in your cam. It may have fallen out and is now in the bottom of your oil pan. That would be good because you can retrieve it and no damage was caused. It may have fallen out and caused one of the chains to jump or break causing the original owners problem in the first place. It may not have been reinstalled after the last cam gear removal. Your guess is as good as any! As far as I know the screw just centers the gear on the cam before you put in the two big bolts.
The shims are just oil and heat resistant rubber washers. You can buy them from some of our vendors or just source your own. O-rings might work as well.

[jhayden]

Good advice from Mike.
A 6x1.0x15mm bolt with split washer belongs in the hole you refer to on the "L" bracket to help secure it rigidly to the head.
While you're in there, shine a light inside the inspection cover to make sure the bolts (with folding locking tab) are in place and in good shape (they can be ground completely away with a ridiculously loose upper chain, but yours is nowhere near that bad).
Some U20s only rattle briefly during startup, so why not try it as is before breaking off the "L." Our U20 doesn't rattle even at hot startups w/o shims, but I check the bracket from time to time just to make sure it's not sneaking anything past us.

[redroadster]

Definitely needs new Sprockets...huh & chain ofcourse, if they missed that wear ,what else ?
Timing chain sprockets on any make should look like the Matterhorn profile

[WHFred]

Thank you all for the advice. Making progress, bit by bit.

Lots of sins from the previous owners to correct

[theunz]

Just to be clear, I was referring to the small hole at 12 O’clock in your last picture. I did not notice the one at 5 O’clock. Good catch jhayden!