Cylinder Compression- or lack of it

[Morrie]

OK, I finally screwed up the courage to do a compression check on my 67 912. I know the engine is tired. Here's what I get:

#1: 120
#2: 145
#3: 100
#4: 150

So, these are some pretty poor numbers, right? I think I am mainly in trouble with the differential between lowest and highest, not the actual values, though #1 and #3 are out of spec.

I drive it only a little and do not have the dough to rebuild it right now. I guess I am looking for some ideas on things to try before I store it or sell it.

Valves are noisy, some more than others. Is it possible that due to cam or rocker arm wear my very careful valve adjustments aren't producing the desired results? A friend suggested tightening them slightly and seeing if the numbers rise.

Any thoughts? Or should I head for E-Bay

Regards All,

Morrie
67 912
Bahama Yellow
127K Miles

[Duke]

If your valves were adjusted correctly before the compression test I would say you need work on #1 & #3. Tightening the valves could burn the good ones you have left. You should be able to hear the valves "working" when they are adjusted to specs. Did you adjust the valves when the engine was cold?

[Morrie]

The engine was cold and had sat overnight. I rechecked later and verified the clearances are correct. Is there anything more economical I can do than a complete overhaul? I see these folks talking about spending 5K on a motor. This old coupe just isn't worth it IMHO.

Morrie

[Griznant]

Well, the numbers are definitely not good, and if you have ruled out valve adjustments, I would say it needs a rebuild.

Knowing that 356/912 motors are just a wee bit pricey, I'd suggest an alternative, but this depends on how creative you want to be, and how much cash you have to work with.

I have a good engine in my 912, and really don't want to run the risk of ruining the original just by driving it around town or on trips, and then forking over big $$ for a rebuild. So, I'm pulling the engine, storing it away, and putting in a Type 4 engine (I have five). Essentially, I'll be creating a 912E but in an early body style.

The engine will fit, but you need to make a new engine hanger, rear tin, use the 914 flywheel and clutch setup, and work out a carb (webers) and exhaust setup.

If you were to find a good 914/bus T4 engine (even a 1.7L), you'd be on the road for less than half the cost of the 912 rebuild, and you could use the time to go through the stock engine while still driving your existing car.

Then again, you could build the T4 up into a hotter 2270 for about $5k, and surprise some 911s.

I like this idea because you don't really modify the original car, you still retain the stocker to replace in the future, and you gain a torquey, very reliable alternative to the typical VW type 1 conversion people do.

Just a thought.

Later,

G

[craign]

Morrie,

I had a similar problem when I fisrt bought my 69. Low compression on 2 cylinders. The car had sat for over 2 years before I got it. the engine had less than 10k on the rebuild.

At the suggestion of a Porsche mechanic I did an oil change and added Marvel Mystery oil to it. I then got to run the snot out of it, getting as hot as you can, and low and behold my compression came up to the 170 range.

Why.....apparently when these, or any car, sit for extended periods a form of "varnish" can build up on your rings and seals. Marvel Mystery oil is a solvent based additive that cleans that junk off.

It was a cheap way to find out I didn't need a rebuild.

Craig

[Morrie]

This car sat for 10 years before I got my hands on it. I had a stuck valve on the 120 lb cylinder that came loose with a ping when I was adjusting the valves.

I have rebuilt the carbs, adjusted the valves, have a new distributor, plugs, plug wires, and points. It has fresh oil in the crank.

Does anyone else see harm in the Marvel Mystery oil thing? Also, how much should I add and how much should I drive it before I change out the oil? Any comments?

[Steve F]

What Morrie said.... I'm interested also

[ron69912t]

I have heard of this product for many years and have never read anything negative about using it. I subscribe to Old Cars Weekly where it is mentioned favorably very often.

A friend of mine uses a little Marlel Mistery Oil in his gas to help prevent vapor lock on his 1956 300SL Mercedes Gull Wing.

My only concern would be pushing a tired engine to the limit to loosen up the rings.

Anyway good luck.
Ron

When I was a kid we ran Bardal, an upper cyl lubricant, through the carbs to smoke up the neighborhood..what fun.

[Morrie]

So.... How much do I put in the oil????

Also, I've heard of dumping it into the carbs of a running engine, letting it choke out, sit for a few minutes, then restarting to clear carbon deposits. Any thoughts on this??

[craign]

From the article linked below....

Detergents And Solvents

Many of the older, better-known oil treatments on the market do not make claims nearly so lavish as the new upstarts. Old standbys like Bardahl, Rislone and Marvel Mystery Oil, instead offer things like "quieter lifters," "reduced oil burning" and a "cleaner engine."
Most of these products are made up of solvents and detergents designed to dissolve sludge and carbon deposits inside your engine so they can be flushed or burned out. Wynn's Friction Proofing Oil, for example, is 83 percent kerosene. Other brands use naphthalene, xylene, acetone and isopropanol. Usually, these ingredients will be found in a base of standard mineral oil.
In general, these products are designed to do just the opposite of what the PTFE and zinc phosphate additives claim to do. Instead of leaving behind a "coating" or a "plating" on your engine surfaces, they are designed to strip away such things.
All of these products will strip sludge and deposits out and clean up your engine, particularly if it is an older, abused one. The problem is, unless you have some way of determining just how much is needed to remove your deposits without going any further, such solvents also can strip away the boundary lubrication layer provided by your oil. Overuse of solvents is an easy trap to fall into, and one which can promote harmful metal-to-metal contact within your engine.
As a general rule of thumb these products had their place and were at least moderately useful on older automobile and motorcycle engines of the Fifties and Sixties, but are basically unneeded on the more efficient engine designs of the past two decades.


http://www.vtr.org/maintain/oil-additives.html

As for how much, go buy a quart and just use that in place of an equal amount of oil. Just leave it until your next oil change, I had over 1k miles before changing it out.

Craig
69-912

[Morrie]

OK, I'll go slip a quart out the bottom and drop in some of this stuff, then drive it for a while and we'll see. I'll keep you folks posted. Hopefully nothing blows up.

Morrie

[Morrie]

OK guys, there's fresh oil in the crank and a quart of MMO replacing 1 of the 20 W 50s. I bet there's only an hour on the motor since I changed the oil the first time after I got the car and it came out black and filthy again. Fresh oil and a new filter, now to drive it a while and see what happens! Hopefully the poor compression on the low cylinders doesn't create a disaster. Wish me luck....

Morrie

[Dieselfitter]

I would be very carefull about breaking loose the deposits in an older engine with a bypass oil filter. I think the end result would be very costly in engine and bearing wear. The rings freeing up on a newer engine that has been in storage for a long time is not the same as regaining compression on an older engine. the latter is not even remotely possible with any additive. See ya Mike

[Green 912]

If you don’t have the $ for a rebuild but the car is running now and you only “Sunday drive” it, then don’t worry about the compression so much. Drive it, enjoy it, and know that you are not really hurting anything. Some times piston chatter is mistaken for valve noise. Are you burning a lot of oil? If so when do you see smoke? Save some motor money and watch for a deal on a 912 motor to come your way. Not too long ago I bought a good running 66 912 motor (Long block, carbs to flywheel) for less than $300. Hook up with a PCA or 356 group! That will save you much in the way of $ and headaches. There is much knowledge in the clubs and there are lots of good folks that will gladly help you.

Don’t get me wrong; I am not a T4 or VW snob. T4s are good motors, I am presently rebuilding a 2.4 for a friend’s track 914, but you have an early 912, not a 914 or a 912E. If you have the time and the connections via PCA or any of the 356 groups you will find that not all good 912/356 rebuilds are $4000+ Pellow is not the only good rebuilder. Yes the parts are more but not much if you compare same quality. There are lots of crappy quality parts out there for the T4 and that can make it look like a T4 rebuild is much less than a 912 rebuild. If your motor is just tired (worn rings, guides and the like) you can have it refreshed/rebuilt for less than you might think.

Don’t run for long on the solvent-based additives, as they are not that good for the motor in the long run. I use MMO to lube my air guns only!

[cbbest]

Marvel mystery oil is a great product for this type of application. I know on small gas auxillilary engines on sailboats it is standard operating procedure to use the stuff pretty much all the time. Salt air, infrequent use, difficult maintenance tends to lock things up. MMO works wonders freeing up sticky valves, and keeping them unstuck.

But then again, these engines (sail aux.) don't see anywhere near the hours a car would, so no, I wouldn't use it all the time as I do on my sailboat.

5K on a rebuild will give you a great engine, but its not your only option. I took an engine out of a parts car, put in new rings ($90), valve seals ($30) and gaskets ($50) cleaned things up a bit and have a fine little engine for now (OK - I also bought webers, powder coated the tin, new wires, ETC.). Lots of little misc. surprises, but other than the carbs, I don't think I spent more than $400 getting it back together. The work was really not that bad. Something to think about...

Cb