Overhaul'n an A4

[Loki9]

Rather than make my introduction thread painfully long, I thought it would be better to document the overhaul here.

To recap, I picked up an A4 at a local boatyard in unknown condition. It looked pretty good externally, it was complete and not horribly corroded, but they couldn't tell me when it had last run or if there were known problems. I decided that running it might do more harm than good, and I would never trust it unless I tore it down and made sure that all was well.

Before starting the tear down I did a compression check:

#1 100psi
#2 97psi
#3 97psi
#4 70psi

When I got the head off, the #4 valves looked dirtier than the others (pictures in the original thread).

I discovered the likely root of the problem with #4 as I removed the valves and found that the exhaust valve spring was broken.

[ILikeRust]

Yes, and?

Keep it coming...

[Loki9]

While the outside of the motor was fairly clean, the inside was another story. When I removed the side plate from the block to expose the water jacket, I found the block packed with black mud and rust scale. I can't tell if the black "mud" is actually mud or just really fine rust particles, but whatever it is, there sure is a lot of it.



The cover plate is really bad and will have to be replaced.


Was the original plate flat on both sides? It's now recessed on the inside and in one spot it has rusted all the way through (arrow).



I can't imagine that this motor was run with a hole in the side of it, so I guess a lot of the corrosion happened while it was sitting.

[Kurt]

By browsing the threads here on the water jacket, you will find that no one really knows what that black crud is in there, but it is normal on an engine that has not been regularly flushed with acid/vinegar/power flushed with water. It is likely a mix of some rust and crud from raw water (organic materials). Either way, this is a great reason to upgrade to fresh water cooling when you rebuild. Fairly simple upgrade for the do it yourselfer and you won't have to worry about that crud building up in your water jackets again.

[ILikeRust]

I couldn't believe the nasty, greasy gunk and crud that came out of my engine block. I am converting to FWC. The kit wasn't cheap, but I like the peace of mind I'll get knowing that I'm not pumping brackish water full of all kinds of organic matter and silt through my engine.

[Loki9]

Interesting..... The #4 exhaust valve lifter is on right. The other seven lifters look like the one on the left. Not sure how it got corroded like that, maybe water came in through the exhaust and down the valve guide?

[hanleyclifford]

Please tell us that the picture in post #3 in the upper right under the deck near #1 does not show a crack.

[Loki9]

Please tell us that the picture in post #3 in the upper right under the deck near #1 does not show a crack.

It's not a crack.


Just a flake of rust, possibly emphasized by the camera's flash. Good eye though, having many eyes on my work is one of the reasons that I'm posting it here. Thanks!

[Loki9]

Here's the stripped down block. No surprises inside, looks really good actually. The cylinders are smooth with no scoring or top ridge. I don't have a mic to measure wear, so I'll have to wait for the machine shop to give me the news there.



Likewise, the cam and crankshaft look to be in very good condition. I don't have micrometers on hand, but I do have a good digital caliper, so I took some measurements with it. I'm not making any decisions based on these measurements, as a caliper really isn't that accurate, but it's all I have on hand right now.

Main journals 1.986" and 1.986"
Rod journals 1.560", 1.560", 1.560", and 1.561"

As suggested in the MMI manual, I reinstalled the main bearing caps and re-torqued to spec to check the bearing clearance. The measurements were 1.988" for both ends, giving clearances of 0.002".

Using the same method on the rod bearings, I found clearances of .003", .003", .002", and .003".



The idler gear spindle is pristine, no measurable wear, with a nice .001" clearance with the gear bushing.


So off to the machine shop it goes. I want the major castings hot tanked and checked for cracks, and I'll have them measure everything.

[hanleyclifford]

Hard to believe that clean block is the same engine! And those specs - a lot of people would consider that almost within acceptable tolerance, especially the mains. BTW, I use calipers to make those measurements and have had no trouble. Looking forward to the remainder of this rebuild!

[lat 64]

It looks like you have a low-hours motor. It was probably abused with little maintenance like the boat it was in. I don't know much about raw-water cooled, but it could be all that gunk is from leaving it soak in the salt with no flushing or love.
Not sure about the black crud, but I am thinking it's a more stable form of iron oxide. More googling on this for me.
That gunk is only reason for hot tanking I can think of. The hot tank will destroy babbit cam bearings and degrade the paint on the inside of the block. If the cam bearings are good, why buy new?
With solvent and then hot hot soapy water you can get an engine mighty clean.
But if that gunk wont come out, then I guess a hot tank is needed. No guarantees there either.

The valve spring seems like the classic rust-from-water intrusion-then-breakage syndrome that Don M. writes about. I can just see the last owner of the boat in the final days of ownership, frustrated, and cranking a motor till the battery is dead and then going home never to return. Poor thing.(the boat)

Great buy,
Russ

[Loki9]

The main bearing clearances are at the high end of acceptable, but at $300 for a new set, I'm thinking I'll reuse them. The wear pattern is normal and fairly even, there is no scoring, melting, or other problems. Except...



I'm not sure what these grooves on the side are. This is the keeper bearing that prevents the crankshaft from moving side to side on its rotating axis. Maybe the grooves are oil paths? They look like wear, but there is nothing I can see that could have made such grooves. So, I'm guessing it's supposed to be like that? Can someone confirm?

[hanleyclifford]

Yes it is supposed to look like that. I have reused mains that looked like that with .002" clearance. No problem. Check your end play when reassembling. The spec is .002" to .003" - I run at .007" no problem.

[Cool Beans]

Very low tech, but they look like oil grooves to lube the bearing face. . .probably serves as a thrust bearing. . .

[lat 64]

They look fine tome too, and if they are within spec, then they are within spec.
To put this in perspective, I found standard bearings in my engine when I tore it open. However, the crank had been ground .010" under. This made for around .007" oil clearance. It had very low oil pressure, but the engine had well over 100 hours running that way, and no damage from lack of lubrication resulted. Just a lot of other poor assembly and goofiness.

You'll be fine as far as these bearings go. Do be sure to check for dings in the crank that resulted from the rod bolts hitting them as you took it apart. Any dings must be polished out.

Cheers,
Russ