Knocking after rebuild

[amikulics]

It's been a few weeks but I finally got my 72 1700 type 4 engine back together.

I had found low compression all around so I decided to do the piston rings. My engine originally used sealing rings at the top and bottom of the cylinders but I ditched the ones on top and lapped the cylinders to the heads. Before ever starting the engine I did a quick compression check and all cylinders were at least 90 (I know compression cannot accurately be measured this way but I wanted to ensure I didn't have any huge mistakes).

Today I got the chance to start it up, however it developed a knocking sound that increases and decreases with rpm. During my rebuild I only did the rings and never split the case which is why I'm hesitant to think its crank-related. The engine also ran and sounded great before the rebuild. Also removing the top sealing ring would raise the compression ratio but I was running 91 octane so this shouldn't be a problem. I've also gone back and checked all the valves. I'm far from an expert mechanic so please feel free to suggest anything.

[SGKent]

As you put it back together did you make sure the piston arrows were all pointing the correct way? Wrist pin circlips in correctly? Double checked? Make sure you still had piston to head clearance when you took the head gaskets out if you didn't add that measurement to the shims at the bottom? Distributor in all the way? Rocker arms and shafts in the correct location and wires clearing the pushrods?
_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[Wasted youth]

[amikulics]

[SGKent]

Pull the plugs when the engine is cold. Take a foot long piece of thick solder for plumbing, straighten it then put it into each plug one at a time until the tip hits the cylinder wall 3 inches or so after it goes in the spark plug hole. Hold onto it just because. Then rotate the engine by hand using the alternator nut. Crush the solder. If you can't crush it then there is no clearance. When the solder is pulled out, the thickness of the solder is the approximate piston to head clearance. Don't forget to remove the wrench from the alternator nut when you are done. Normally engine builders use clay for that during the build process if clearances are tight. I don't know anything but solder that will work but anything that crushes, doesn't fall apart, and doesn't stick can be used. Maybe someone else knows a product like a malleable plastic or clay in a sleeve etc that doesn't ooze out.
_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[Wasted youth]

[timvw7476]

Did you hone the cylinders when installing the new rings?
the 1700/1800 really likes scuffing the thrust side of the piston skirt,
when you re-ring you can be rewarded with piston slap when cold &
warning up. Not the end of the world, but it comes & goes with thermal
warm up. Or you've got an arrow on a piston crown pointing away from the
flywheel.

[Zed999]

Did you loose any washers while you were fitting tineare, manifolds and carbs?
Been there done that but I think you would have stopped cranking after the first hit.

[aeromech]

No offense but are you doing this on a low budget for a reason? My question is being asked because it's a damn lot of work to go in and just do rings only to have issues like you're having. Did anyone look the heads over? Did anyone calculate the compression ratio? When you add new power to the top end and don't do anything to the bottom end it puts strain on all the old parts. Sometimes you can get away with it, sometimes not. I leave long block building to the experts because of what I said. It's just too much work to do over and over until you get it right. I'm currently working on a 1973 engine that just came back from the shop. Cost was $2200 for a rebuild. We'll see how things go. Crossing my fingers because this is the first time I've worked on one of their rebuilds.

_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[74 Thing]

What shop did you use?

[aeromech]

The shop is called Brothers VW Machine Shop in Ontario California

http://www.brothersvwmachineshop.com/
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[KTPhil]

[aeromech]

Those are the kind of mistakes a person only makes once and people can be told over and over to not make that mistake but until they do......
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[amikulics]

Quick update: I posted two videos of the knock, I'm leaning towards piston slap.

https://youtu.be/_jafZznQOYA

https://youtu.be/F9WqbF7zl7c

[SGKent]

Piston slap is a really light knock - that is why they call it a slap. its more like a double rattle than a knock. To me I think your exhaust is leaking.
_________________
Canned Water - the new California approved parts cleaner (except in a drought in which case rub it with sand).

George Carlin:
"Most people don't know what they're doing, and a lot of them are really good at it."

Skills@EuroCarsPlus:
"never time to do it right but always time to do it twice"

1971 deluxe (sold)
1977 deluxe

[amikulics]

[SGKent]

[Mispeld]

That sounds like a collapsed hydraulic lifter(s) (if you have hydraulic lifters). I personally think they sound similar to an exhaust leak. That noise doesn't sound like piston slap or "pinging" as we call it when it's too far advanced. It's possible with too much compression to need to use higher octane but I don't think we are experiencing that.

What type of lifters do you have?

Pull your valve covers and push on the pushrod side on the rockers with a large screwdriver or whatever.

Check your valve adjustments.
_________________
Tom
1977 Westy. 2.0 Fuel Injected.

[amikulics]

[white74westy]