Need help rebuilding our 912 engine
 

Our 912 engine has been a real mess lately.

Its always run a little rough, lots of spitting, popping, backfires... we thought it was ignition so we went with Pertronics and a new coil.

The Solex carbs were giving us trouble so we swapped in a set of Delorto's. We found a leaky accel jet, bad float bowl adjustment, and we made sure to swap in the correct main jets.

After all that, it never ran worse. The car was undrivable. The syncrometer said that the back throats were pulling much less than the fronts, on both sides of the engine and a compression test showed the passenger-side back cylinder was ~90psi where the others were ~120. I decided to pull the motor and pull off the heads.

So here we are, heads are off, and pulled the exhaust valve out of the passenger side rear and it looks fine, not fried. It does look like the valve guides on the exhaust valves are starting to leak, but other than that I can see no issue. Note that each head has an exhaust valve that is dark and one that is tan. Also note that the 2 of the pistons have shiny clean areas where the other two are full dark. I also noticed that the cylinders had just a touch of scoring and i can clearly see a cross-hatch pattern, like someone took a grape hone to them.

I honestly don't know what to do from here. Im planning to hot tank the heads and get them all cleaned up, but where do I go from here?

Thoughts? Suggestions? HELP!

Pistons: Mahle 82,46
Intake ports: roughly oval 32x34mm
Engine code: 32984 729/1

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That low psi troubles me.

I suggest at minimum, having the cylinders honed, new rings and a valve job.

Then attack the timing and carbs.
If the carb problem returns, move the carbs from side to side and see if the problem follows.

Keep us posted.


KT

I'd run this by the guys at 912bbs.org.

Bad rings no contest:(:(:(

+1
when the carbon is washed away from the top edge of the piston it is a sign of worn oil control rings and usually the compression rings will be worn also.
Raw fuel, from no ignition (bad plug, ignition wire, to much fuel etc.) will wash the lubrication oil from the cylinder walls and wear out rings fast.
You had fuel issues which accelerated the ring wear.

A few more pics:

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Lots of stuff going on here.

Sorry to be the bearer of bad tidings, but that is NOT a 912 motor.

Pistons appear to be flat-top 1600N, 7.5:1 CR (not much compression even when brand spanking new)

Heads have no cast gusset in the valve gear area and stamped 58.0cc which both indicate early (pre-62). Probably A or B Normal heads.

Cast iron rocker stand, also indicates earlier motor.

All this makes me conclude this is very likely a 356 A or B motor from a Normal. 7.5:1 cr, 60hp. Can't see the ports, but I can imagine they are very small for your Dellorto manifolds and have a big mismatch. The Dellortos are a poor choice for this motor and will never run right. Zeniths would be correct.

P/C's will be shot. I guarantee it. Don't even consider honing and re-ringing. Even if you could, you would still have a 60 hp motor, overcarbed and unresponsive. First step would be to figure out what you have. What is the SN on the oil filler stand? What rods are in it. What crank? Maybe it can be turned into something worthwhile, or maybe it would be best to find a different motor.

Absolutely nothing wrong with a 1600 Normal. I love them and have a couple. Cool running, smooth, long lived little guys. But your 912 is several hundred pounds heavier than the 356 this belongs in, and is going to be feel pretty gutless even on the best of days with this motor.

DG

Its probably a hodge-podge of parts, the case is full of ARP fasteners (not the studs unfortunately).

Pistons: Mahle 82,46
Intake ports: roughly oval 32x34mm
Engine code: 32984 729/1

Clearly the engine stamping says its a marine use case, but i was really hoping that the rest of the engine was not original, heh. You'll also note that there is not venting hole in the head, thought that was kind of interesting.

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Bad news, good news... I just need news at this point.

You're absolutely right about the intake ports, they are quite smaller than the Dell manifolds. Thats a shame , the Dells are nice units.

There is no serial on the oil filler stand, just the case stamping behind it. Not sure on the crank.

Any idea what it might be worth? We've toyed with a few different powertrain ideas, now might be the right time to let this one go.

Whats the stamping on the case (616/??). If you take off the front cover there will be date stamps on both the cover and the main crankcase. Could be an unstamped 912 front cover on an earlier case. Or some other combination. Definitely need to figure out what you have before deciding what route to take fixing it.

729/1

Are you referring to this cover?

http://forums.pelicanparts.com/uploa...1361374853.jpg

Well that was unexpected! You don't even have a car motor :eek: 729/1 was a late '50s 1600cc intended for inboard motor boats. Very funny! It will have an A crank, early rods, small oil pump, low compression, mild cam. Now I'm puzzled how it was adapted to a 912 and the rear motor mount bar. Look around the front cover carefully. The serial number may be there, but in a different place than usual.

Seen a lot of industrial engines in 356s over the years, but not many made them into 912s. Still can be made a viable motor for the car though. Just way down on power.

Most likely a 912 timing cover mounted possibly to a early engine case. Oil pump is the later large size and has no tach cable joint.

The question remains: What do I do with this thing!?@#%

Sounds like the very least it will need the cylinders honed, possibly new rings, and a different smaller set of carbs bolted up.... and then I'lll have 60hp on a good day.

Maybe the cylinders are not salvageable? I hope I don't have a big paper-weight on my hands here...

What are the other engine options you are considering?


KT

Aircooled would be ideal, but if the costs are as much as I fear they might be we might consider a larger swap (13BT, STi, etc). You can't beat the $/hp of some of the modern engines and the weights are less too... though Im not excited about running cooling lines and a radiator to the front of the car.

The original plan was to get it on the road and just enjoy it for a bit while we save up money for a larger swap, but at this point we might as well jump right in. First, though, we gotta figure out what to do with this motor!

How about building a boat to go with it? :)

http://forums.pelicanparts.com/uploa...1361394765.jpg

Seriously, hold onto it. Looks like they only made 241 of those if you believe the 356 registry.

Now finding the outboard is going to be tough. . .

http://forums.pelicanparts.com/uploa...1187799802.jpg

"Seriously, hold onto it. Looks like they only made 241 of those if you believe the 356 registry. "

Yup, but there's only 4 guys on the planet so far out there as to collect these, and they already have them. Rare does not equal valuable in this case (pun intended) Once a boat motor....now a boat anchor:(



"Sounds like the very least it will need the cylinders honed, possibly new rings, and a different smaller set of carbs bolted up.... and then I'lll have 60hp on a good day. Maybe the cylinders are not salvageable? I hope I don't have a big paper-weight on my hands here..."

Maybe not completely hopeless. Not a big fan of the Chinese big-bore sets, but it might be a reasonable low-cost option here. IF the crank and case are good, you could pick up a set of C/912 rods and use the big bore set. The A crank will limit you to about 5000 RPM max (4500 would be safer). A low end torquer cam and the small port heads could work together for a grunty little motor. Find someone to swap the dellortos for zeniths. I doubt you could ever quite reach the 90 hp of a 912, but you might have more torque and it would be quite driveable. If you attempt to do any more than that you'll be better off buying a 912 core for the starting point.



"Most likely a 912 timing cover mounted possibly to a early engine case. Oil pump is the later large size and has no tach cable joint."

This is something bothering me. How does one fit a 912 timing cover onto an early case? IIRC, the oil passages shouldn't line up.

Ok, I've ordered a set of Zeniths with manifolds, fingers crossed they smooth things out.... anything will be an improvement at this point.

Question though: I've pulled the heads off the engine and now Im into reassembly... should I have them machined before mating them back up with the cylinders? Thoughts, concerns, etc?

Also, what is the proper torque spec for the head bolts? Where can I find that information?