Water ingress in cylinders - what part gives in first?
 

Due to a series of unfortunate factors (the most significant being my lack of brains), rain water got into at least two of the cylinders in my 2.7 engine. Apparently, this didn't do it good. It failed the compression test, and a cylinder leakage test indicated a leak between the cylinders and cylinder heads. It appears that the nuts at the cylinder bolts have loosened, and at the two rearmost cylinders, they were really loose. I guess that when I cranked the engine, the pressure from the water made this happen.

Now, the question is what part gives in first - Does the bolt stretch, the threads tear or the engine case crack/deform? New bolts with Helicoils were installed not long ago.

Is there any way to test the strength of the bolt assembly? As opposed to dismantling the cylinders?


Einar

Magnesium case, correct?

If so, and you hydrolocked the cylinders, most likely pulled the threads in the case. Since the head nuts weren't broken away from the studs it's likely the studs are intact. You can try to tighten them up to test their ability to reach torque spec.

In Anderson's book he mentions even helicoils will fail under this scenario, therefore his recommendation of timeserts over those, but those have their limitations too.

I'm sure Henry at Supertech has an up to date solution for this.

That's right, 4R. And your statement confirms what I expected.

So I probably need a new case? This one was modified and line bored for 2500 USD a couple of years ago...

Einar

Before going too far please await more informed speculations than mine.

Most certainly you would want to pull the heads and cylinders to examine the potential case damage if you cannot get the heads torqued to spec.

There are a number of regular builders in the forum, they will have some ideas from which to choose.

Helicoils are garbage, you need to use case savers. I would pull the motor and investigate.

Pulled studs are a common issue for mag cases, it does require a full teardown to have the case machined. It’s also possible some head studs broke.

Either way, disassembling the top end is a next step to see what’s failed.

A 4R case was never meant to be a 2.7. When case was line bored it should have been timeserted
Bruce

Actually before dissembling, it’s worth trying to tighten the loose cyl head nuts before disassembling. It’s likely that they’ll just spin (pulled or broken stud), but it’s trivially easy to check.

Thanks for all replies.
Einar