FRporscheman

My '84 just blew its head gasket. I tried to start it, and it just turned over a little bit and stopped. I pulled spark plug #4 and cranked it again, and water sprayed out of the hole and it fired right up. I put the plug back in and left it alone.

Then I decided to fix the car, so I wanted to pull it into my driveway. I got lazy and left the plug in and tried to start it, and again, it turned over a little bit and just stopped. So again I removed plug 4 and started it.

Obviously it was hydrolock in cylinder 4 preventing the engine from turning over. Should I be concerned about anything? Should I have anything checked while the head is off?

Olli Snellman

Yes.
You can easily bend a rod with hydrolock.

Grandpa#3

I hope I'm correct when I say you have forged rods. If so you should be OK, but don't push your luck again.

Cheers,
Larry

931guru

Even forged rods will bend under the power of a starter and a hydrolock.

Oddjob

I am aware of an S2 motor that hydrolocked when started; after replacing the HG, the engine thru a rod the first time it was rev'd up. Rod had been cracked when it hydrolocked. Forged rods may be ductile enough to deform/bend w/o cracking, but a bent rod is not a good deal either.

Good luck.

Van

When you have the head off, carefully check deck height with a nice straight edge and feeler gauges. That might give you an indication if the rod is bent.

ZR8ED

Wow! that is news to me. I would have answered a tentative "it is likely not damaged". Just thinking of all the force that the connecting rod endures during compression and then combustion, I would have thought a small starter motor could not put out enough force to bend anything. Especially when it can only turn the crank a partial rotation at a whopping momentum generated by 300rpm.

Not that I would recommend trying to repeatedly start it and risk damage.

Thanks for the info!!!

dontnow

Check the deck height like Van said. If it is dead on, your are fine; if off even a little, pull it apart to inspect.

For ZR8ED, "it is likely not damaged" as you have high quality parts inside your engine; but check to be sure!

pettybird

My buddy bent a rod in his Plymouth's 440 when water got into his air cleaner during a VIOLENT rainstorm. Those rods are huge compared to a 944's...

hacker-pschorr

It's also a good way to crack a cylinder.

The size of the rod is irrelevant, it's the construction and metallurgy that matters. You can make a sintered rod the size of an oak tree and it's going to be weaker than a stock 951 rod.

F18Rep

I'm betting no damage. But lets assume this could do some damage, is there potential for damage using the old trick of rope down the cylinder (in lieu of a flywheel lock)? It seems like kind a neat trick but always wonder about that when it comes up....Bruce

PS... I've seen two other cases where soemthing kinda like this happened with no damage, first was one of my 951's that had a "starter thunk" problem, you know caused by a loss of ground on the sensor shield - which in turns allows a starter pulse to fire one plug early enough that the crank backs-up.

And second, on my 77 911, I had a bad injector and it would fill up a cylinder with fuel - same outward symptoms - it would start to crank and just stop.

There was another guy on here a couple of years ago that broke a cylinder - I think in his case the engine was running and we concluded that an injector had hung in the open state, allowing way too much fuel.

FRporscheman

Thanks for all the responses.

I honestly thought everyone would tell me it's OK. I didn't think the starter would be strong enough. This is an '84 with the old fashioned large-body starter, which I think has less? torque than the later small-body ones. Also, being an '84, it supposedly has cast rods. And FWIW, the engine didn't make a whole turn, it only turned for a split second, so maybe it built less momentum than you thought.

Van, thanks for the tip, I will go get a straight edge and check the piston height.

If I have to replace the rod, I have a set of 944 2.7 rods, and a set of 944 S2 rods, will any of those rods work? Any reason not to do a full rebuild while it's open?

jameso

Hi, I dont post often but I'm pretty sure the starter is designed to fail in a hydrolock condition.
Had a 968 engine, the early one with the weak rods. I was running megasquirt which locked into injector test mode, filled the cylinders with a fair amount of fuel and it just wouldn't crank over far on the starter.

No damage done, a running engine would have been another story though.

The rods are all swappable. I currently have 1986 2.5 turbo rods in my 1992 968 3 litre bottom end.

s14kev

Cranking with a starter is unlikely to bend a rod. Since the rotating assembly (crank, rods, pistons) is being accelerated from standstill it really doesn't have much inertia behind it. The starter won't have enough torque and the pinion/ring gears are likely to shear first.

However when you describe water shooting out of the plug hole and it firing up then I would be concerned. Doing that was a bad move. Even with the plug hole open, maximal flow of coolant through that size hole (spark plug orifice) is unlikely to exceed compression volume in that cylinder. Combustion pressure driving the crank most definitely is enough to bend a rod.

So the answer is maybe you did, maybe you didn't. Easy enough to check though.

FRporscheman

jameso, good to know. But what I meant was, can I use a single 2.7 or S2 rod on #4 with my original 944 rods on #1-3? Mix-matched? I suppose if I'm changing one rod, I could change them all easily enough.

kev, it took a few cranks to start, so I am certain all the water was ejected from 4 before the combustion started in 1-3.

I measured the piston height of #4 and it is completely level with the cylinder wall deck, just the same as #1. I couldn't fit my smallest feeler gauge which was 0.004. I don't think any gauge would fit, it looked and felt completely flush.