Itinerant Air-Cooled

Here's a weird one.

I have a bone stock 1600 engine in my 67 bug. It has 7k miles on it since rebuild. It's an occasional driver. So, it sat for about two weeks since I last started it. When I went to start it this morning, I noticed the battery was a bit low as it turned the starter over. When the engine caught, it made a really deep knocking noise that startled me. I shut it down. I then started it again and it made a knocking sound again like it had no oil pressure and then suddenly cleared up and all the noise subsided. It's NEVER done this before. In fact, in 35 years of aircooled VW ownership, I've never had a VW engine do this.

The knocking noise sounded really deep in the engine like the crank or a rod. I let it warm up and it ran perfect w/absolutely no noise, knocking or anything. I did a few errands today, putting about 20 miles on it, including a freeway run. Each time I've restarted it on the errands, it's acted perfectly normal w/no noises or knocking.

I pulled on the main pulley and have no abnormal end play. The engine has 10-30 oil in it. Again, it runs absolutely perfect, no knocking or other sounds.

So, what the heck was that?!?!

Thoughts?

wcfvw69 wrote: So, what the heck was that?!?!

Thoughts?

You woke up the engine gnome.

Im no expert on type 1 engines, but I would think that it possibly had massive amounts of air in the oil galleys, or maybe a main bearing shifted until heat and expansion forced it back in place, loose dowel on the mains? Whatever happened, starved its oil supply. Best of luck to you, but it doesn't sound good for the long-term engine health. I would pull it out and get in there deeper.
Scottie

wcfvw69 wrote:Here's a weird one.

I have a bone stock 1600 engine in my 67 bug. It has 7k miles on it since rebuild. It's an occasional driver. So, it sat for about two weeks since I last started it. When I went to start it this morning, I noticed the battery was a bit low as it turned the starter over. When the engine caught, it made a really deep knocking noise that startled me. I shut it down. I then started it again and it made a knocking sound again like it had no oil pressure and then suddenly cleared up and all the noise subsided. It's NEVER done this before. In fact, in 35 years of aircooled VW ownership, I've never had a VW engine do this.

The knocking noise sounded really deep in the engine like the crank or a rod. I let it warm up and it ran perfect w/absolutely no noise, knocking or anything. I did a few errands today, putting about 20 miles on it, including a freeway run. Each time I've restarted it on the errands, it's acted perfectly normal w/no noises or knocking.

I pulled on the main pulley and have no abnormal end play. The engine has 10-30 oil in it. Again, it runs absolutely perfect, no knocking or other sounds.

So, what the heck was that?!?!

Thoughts?

That was your main bearings without oil. The engine lost its "prime. Knock off the 10-30 wt oil PLEASE.
Colin

Amskeptic wrote:

wcfvw69 wrote:Here's a weird one.

I have a bone stock 1600 engine in my 67 bug. It has 7k miles on it since rebuild. It's an occasional driver. So, it sat for about two weeks since I last started it. When I went to start it this morning, I noticed the battery was a bit low as it turned the starter over. When the engine caught, it made a really deep knocking noise that startled me. I shut it down. I then started it again and it made a knocking sound again like it had no oil pressure and then suddenly cleared up and all the noise subsided. It's NEVER done this before. In fact, in 35 years of aircooled VW ownership, I've never had a VW engine do this.

The knocking noise sounded really deep in the engine like the crank or a rod. I let it warm up and it ran perfect w/absolutely no noise, knocking or anything. I did a few errands today, putting about 20 miles on it, including a freeway run. Each time I've restarted it on the errands, it's acted perfectly normal w/no noises or knocking.

I pulled on the main pulley and have no abnormal end play. The engine has 10-30 oil in it. Again, it runs absolutely perfect, no knocking or other sounds.

So, what the heck was that?!?!

Thoughts?

That was your main bearings without oil. The engine lost its "prime. Knock off the 10-30 wt oil PLEASE.
Colin

What the heck? Why would it suddenly lose it's prime Colin? Again, I've NEVER had a VW engine do this before. Can you expand on this a bit Colin? Just want to understand better.

Thanks Colin

You might just be needing a heavier grade of oil. 10 / 30 is pretty light stuff in a ACVW. A multi grade you might try is 20 / 50 regular. You might consider straight 40. From what you describe, I would guess a rod had gone dry and knocked until oil got pumped in. Damage? Can't say without seeing, but sometimes not enough damage was done to the bearings to blow the engine for thousands of miles, then again if there is enough damage, it might let go in a few hours or miles. If it was me, drop the engine, pull the heads pistons and jugs, then it would be easy to find out your rod brgs. condition. Any slop you can change the rod brgs. and if need a rod without a complete tear down. As long as the crank didn't get scored.. Ainokea

wcfvw69 wrote: What the heck? Why would it suddenly lose it's prime Colin? Again, I've NEVER had a VW engine do this before. Can you expand on this a bit Colin? Just want to understand better.
Thanks Colin

Really not a big deal. Relax.

Imagine a finger over a straw. You can hold a column of liquid without a problem so long as the straw doesn't have a leak. Stick a hole in the side of the straw, the column of liquid will drain out.

You merely heard a crankshaft not suspended on the hydrodynamic oil film until the pressure filled the bearings. I think your clearances might be a bit much for an only 7k engine, but hey. We of hydraulic lifters experience this drain down also. All I am suggesting is that your lubrication system allowed the oil in the galleries to "drain down the straw".

Sometimes low oil level will allow the pick up tube right above the strainer plate to introduce air into the pick up tube and all night little air bubbles will slowly migrate up to the pump, to the galleries, to the oil cooler while the oil slowly drains down into the sump.

Sometimes, a pressure relief piston will allow the same thing to occur. It is natural and it becomes more frequent as the engine slowly wears out.

A first defense is to keep your oil level and viscosity up. For Type 4 engine owners, a nice anti-drainback oil filter helps.
IF you find this thumpy start become frequent, I would guess that the pick up tube has loosened in the right crankcase half . . . you would then keep your oil level a little high, you would keep your viscosity up, and you would start the engine gingerly in the morning, and you would be careful not to push the engine too hard at high rpms because air bubbles will be showing up.

Again, relax, be aware, and let us know if this symptom crops up chronically.
Colin

Amskeptic wrote:

wcfvw69 wrote: What the heck? Why would it suddenly lose it's prime Colin? Again, I've NEVER had a VW engine do this before. Can you expand on this a bit Colin? Just want to understand better.
Thanks Colin

Really not a big deal. Relax.

Imagine a finger over a straw. You can hold a column of liquid without a problem so long as the straw doesn't have a leak. Stick a hole in the side of the straw, the column of liquid will drain out.

You merely heard a crankshaft not suspended on the hydrodynamic oil film until the pressure filled the bearings. I think your clearances might be a bit much for an only 7k engine, but hey. We of hydraulic lifters experience this drain down also. All I am suggesting is that your lubrication system allowed the oil in the galleries to "drain down the straw".

Sometimes low oil level will allow the pick up tube right above the strainer plate to introduce air into the pick up tube and all night little air bubbles will slowly migrate up to the pump, to the galleries, to the oil cooler while the oil slowly drains down into the sump.

Sometimes, a pressure relief piston will allow the same thing to occur. It is natural and it becomes more frequent as the engine slowly wears out.

A first defense is to keep your oil level and viscosity up. For Type 4 engine owners, a nice anti-drainback oil filter helps.
IF you find this thumpy start become frequent, I would guess that the pick up tube has loosened in the right crankcase half . . . you would then keep your oil level a little high, you would keep your viscosity up, and you would start the engine gingerly in the morning, and you would be careful not to push the engine too hard at high rpms because air bubbles will be showing up.

Again, relax, be aware, and let us know if this symptom crops up chronically.
Colin

Relax.. relax.. RELAX you say!?!?!? :)

You do a great job of explaining things Colin. Thanks for taking the time to esplain it so well. As I mentioned, I'd never experienced this before. On the next oil change (it's full), I'll check the pick up tube bolt to insure it's tight. As far as the bearings tolerances, when I built this engine, I used the plastic, squish "stuff" on each crank and rod bearing to check the tolerances. It was all in spec. I had the crank and the rods, flywheel and pressure plate all balanced by a well known shop. They also measured the crank and line bored the case while it was there. They then sold me the bearings too.

I'll monitor it and see if it does this again.

Again, thanks!

If you find a Volkswagen engine losing its prime, I frequently proffer the simple solution of "drive it more."

Uhh, which one of you is the gnome?

Robbie10w30also

SlowLane wrote: You woke up the engine gnome.

...laughing, somewhat uncontrollably, at what might be the most classic IAC photo ever.

miz

asiab3 wrote: Uhh, which one of you is the gnome?

Umm, okay. Just want to make certain that classic photo is properly attributed to our friend jivermo from last year's IAC circuit.
I'm not nearly as pretty as either of those guys...
(10W30 winter, 20W50 summer, using Amsoil Z-Rod for the extra dose of ZDDP)

Well, it's strange to have that popup gnome appear as you are revving the engine up. Especially when he has the same sartorial tastes in work shirts as oneself.