Engine Rattle around 4k rpm, timing chain?

[AmishRoadster]

Last year I got a 68 2000 up finally got it up and running. I noticed though that when I got into higher RPMs (around 4000) I would get a loud rattle sound, presumably near the front of the motor. The rattle is only when it gets into the higher RPMs. I am guessing it is maybe the timing chain?? I just pulled the motor/trans to work on some leaks and wanted to check the timing chain. From what I have read here it sounds like I should check the evil “L” bracket, which looks to have already been removed. Is there a process to check the timing chain slack? Since I am new to working on these cars I posted some additional pics of the motor incase there is something that stands out to check while I have the motor out. Thanks for any help!

[unklpat]

Rotate your motor clockwise from front to TDC and check the amount of tensioner shaft exposed. Your upper sprocket shows significant wear. Way better to change sprockets and chains now, than to have to do it in the car later. Pat

[Gregs672000]

Agreed on the cam gear wear, probably the others too. Plan on replacing all, along with chains.
Welcome! Sorry for the bad news...

[spyder]

I looked at the pictures and I disagree that the gear or the chain need replacing. I would definitively shim the tensioner shoe to eliminate startup chain slack, by the way, not the worst I have seen. The chain usually makes noise at idle warm when the oil pressure is the lowest, hence shimming. This is aggravated with higher lift cams. At 4k rpm I'd be looking at timing / mixture issues.

[theunz]

It’s really hard to determine gear wear from the angle of your photo, but it does look, while not to bad, there is some. The gear will wear on the side that is pulling the chain, so how far off being symmetrical the “U” shape is will let you determine wear.
I agree with Spyder that your noise at upper RPM’s isn’t the typical death rattle so commonly referenced. Even with a fresh rebuild including all new gears, chains, and tensioners my engine rattles a little at 4 or 5 thousand.
If however your budget allows and you’re not sure of the conditions of your timing components, now is the time to replace them. The prices and options now are much better than they were 5 or 10 years ago. A broken chain repair will cost much much more than the cost of replacing everything now.

[Gregs672000]

I hear you on the gears, but they look undercut a fair amount for a cam gear. With that much wear I'd want to see the others which in my experience have shown more undercutting. I've run used gears for many years, but with reasonable price and availability now, and being at this point, I'd consider changing all.
Loud rattling at high rpm (from ping or knock?)... pretty hard to tell with only that info. If it were load based, then we could consider improper ignition timing or low grade fuel. Does it happen when you push the accelerator (increasing load), or rattles regardless? If my engines going to ping, its most likely at about 3000 rpm and pushing it hard there. Has timing been checked at 3000 rpm with a timing light (theory: too much advance; smog distributor set to non-smog initial timing). Does it backfire though the carbs or surge/stumble when you accelerate (suspect lean fuel ratio)? Tensioner should be shimmer but if it's loosing oil pressure at high rpm there's some other issue I would think (leaking tensioner gasket) but tickling sounds are usually the chain striking the L, and his is cut off already, so what's making the noise? Are the valves adjusted, or too loose? Could something else be vibrating? Is the crank dampener in good condition?
Keep posting... We're here to help!

[redroadster]

You can install a new chain, run it in ( takes 2 techs ) if it set for yrs the chain can rust on the pins
Need to see the crank gear ,At Datsun they pulled U20s with severe work crank gears ,they couldn't believe still ran some jumped the sprocket and damaged it but put back on anyway because of the extra time /$

[AmishRoadster]

Thanks everyone for the responses, I’ll try to answer what I can! As a heads up I am a novice when it comes to working on cars, so I might have a bunch of stupid questions/responses.
I did not hear any noise during startup or idle, only when at higher RPMs. Unfortunately, I never tried to narrow down the sound while not driving it. In hindsight it sounds like I should have revved it up in neutral to see if the sound was still occurring.
I don’t think it is a bad fuel issue, I had the tank gas repaired and cleaned along with all new fuel lines.
I did replace the distributor with one from east coast roadsters because it did have a smog distributor when I got it. I forget what the new one is set at, I think 16 degrees?? I did not see what the timing was at 3000 rpms though, only when at idle. I did not notice any backfiring or surging when accelerating.
I did not notice any drop in oil pressure at higher RPMs, I think it was increasing as the RPMs went up.
I did check the valve clearance and they seemed good (assuming I did it properly!).
Not too sure about the crank dampener condition, is there something I should be looking for?
Regarding the incorrect mixture question. The carbs I took apart and cleaned, but they have not been rebuild. Also, I just took the exhaust manifold off and when I shined a flashlight from the outside around the manifold I noticed all kinds of pin holes and cracks.
Could incorrect timing, old carbs, and leaky exhaust manifold possible cause a loud noise? To my untrained ears it sounded like a chain slapping against something metal. Not sure what else could make that kinda noise.
I was only planning on getting the carbs rebuilt while I have the engine out and fix a slipping clutch with a leaking transmission, but now it seems the exhaust is toast. Don’t think I will be able to get to the timing chains and gears this time around, but seems like it moved up in the list of things to do.

[nismou20]

The rubberized chain guide material still there? Valve clearance clatter? Any chain wear marks underside of Cam cover? That’s a head scratcher!

[Gregs672000]

I'm wondering if there was something else rattling, like an alternator mount or the crank dampener failing (just guessing on the crank dampener... take a look at it and see if the rubber between the two metal parts appears torn or loose).

[jrusso07]

As Greg said, could be accessories rattling. My carb heat shield would rattle on de-acceleration due to a loose mounting bolt. Also, pin holes in the exhaust can cause air whistling and chirping noises. Did you have the air galley still installed (assuming you had the smog head with the smog distributor). Those too can make chirping noises if the air pump is removed or not functioning. Might sound like a rattle if the frequency is high enough...

[JT68]

The chirp from the (wrong type) emission exhaust plugs is really only noticeable around idle. Carb HS is a very good suggestion, they are notorious for cracks and rattles (at various RPMs). The cam sprocket doesn't look worn enough to need emergent replacement-if at all.

Is the "rattle" only while driving/under load? or also present while revving the engine in neutral?

[unklpat]

I would rotate the motor to TDC, then check the play in the chain. All of the slack will be on the passenger side. Pointer on timing cover lined up with big mark on harmonic balancer, cam gear screw should be straight up. Then you will see what is happening while running, as well as how far out the tensioner is. take pics from straight on, and looking straight down. Adding shims is masking a problem, and pointless with no evil L. Pat

[Gregs672000]

Agreed PAT, except on the shims masking a problem... they're really only needed at start up when the tensioner doesn't have oil pressure and the spring can't control the chain... it will slap like crazy and could jump. Agreed, not likely the source of the high speed rattle though... I'm leaning towards heat shield type stuff!

[unklpat]

Agreed Greg, but there would need to be way more play than shown in the pics so far. Let's get the motor to TDC by rotating it the normal direction, then look at the plunger from above. If the chain is real loose/worn it could be flopping fore and aft also. Pat