Ticking from my GT40 @ GL

I believe according to the mechanics that Rob's engine only had moments to live before that piston/rod assembly went kablooey.

I seem to have the same ticking problem, went out yesterday and made a full throttle run. shut engine off and when restarted noticed a ticking sound. On idle its not as loud as when its increased to 1500 or so and also noticed its got a double tap sound when returning to idle. I am 40 years master certified technician and have found this post. I will bore scope and compression and leak down today,
If it is the same piston skirt sound I would like to know if anyone knows the root cause (lean) and what can be done to prevent this after the repair. 1997 sport nautique 285hrs. Somewhere I seen reference to a PCM service bulletin for piston shrinkage, if anyone has a copy or direction for the repair of the root cause. Sorry to jump ahead without inspection, but think this is probably whats wrong. Also if reboring the engine, any suggestions on piston replacement that is better (teflon skirts)? Thanks

Did he have to bore the engine the first time, I can check the fuel pressure. Do you know if PCM has any problems additionally I should be aware of, don't want this to reoccur. Or if you would take a call I would PM you my number, thanks

So why did only the center cylinders overheat because of the impeller chunks in the thermostat housing?

cooling water flow was restricted with very little flow to thermostat port, ( housing on top of thermostat that hose from raw water pump connects to has an opening in two directions, one going to feed engine cooling water flow) with restricted flow, the four center cylinders are the last to get cool water and the first to heat up. #2 piston suffered detonation as most likely all the cylinders. # 2 failed, other center cylinders just started to go, but would have still been OK if caught now, but it was to late for #2. All pistons need replaced and bore 30 over, if 30 wont clean it up then 60 is to far, new block time.
I have pictures of water flow thru restricted housing the with restriction removed. Hooked hose to housing to test. Outcome surprised me, didn't see exactly how restriction effected flow until I tested it with water.

the four center (middle) cylinders are #2-3-6-7.
Cooling water from the lake enters the engine from the raw water pump.
When it enters the engine it cannot be everywhere at once, if you put dye in it and could see the hydrodynamics (flow thru the engine) you would see cylinders 1-4-5-8 get the coolest water first, also because the center cylinders are surrounded by the outer ones they run a little hotter (a cylinder on each side of the inner ones and only one side on the outer ones.
I guess I should have said middle cylinder's
Due to restricted flow, cooling was marginal, and #2 was the weakest so to say of the middle cylinders.
This is not to say that it could not have occurred in any cylinder, but to point out why it was in the middle

the openings in the head gasket restrict coolant flow till all the area around the cylinder walls are full and only then does the coolant flow up into the heads coolant passages and back to the thermostat, the holes are designed to restrict coolant flow so its more or less equalized as it moves up into the heads and back to the thermostat, if the holes in the head gasket were not slightly restrictive the front cylinders would be much more effectively cooled as coolant would take the fastest and easiest route of least resistance, having a restrictive head gasket makes all coolant flow paths roughly equal.
With that said, it is not that only the center cylinders overheated, I]m sure all cylinders temperature were rising, It was my way of explaining the additional rise in the center cylinders. Normally water flow thru the small block provides very good cooling. But when a restriction reduces water volume to the point detonation occurs the engine temperature is rising, the center cylinders share the cooling water with a cylinder on each side of them. #1 shares with 2 on one side, 2 shares with 1 and 3, 3 with 2 and 4, 4 with 3 on one side.
The restrictions in the head gaskets do not change, water flow for all cylinders is still at a reduced rate due to restriction and the temperature rise in the center cylinders is faster due to there sharing of cooling water.
Maybe instead of getting into the woods on detonation effects on engine cooling we should raise the more important point that i expect impeller failure occurs often enough and errant pieces of the impeller can and will plug or restrict coolant flow. Complete restriction will be easy to see on the temp gauge. But partial restrictions may go on with only seeing slight gauge rise. At full throttle you may glance at the temp gauge most will be looking where they are going. After several times. who knows how many, detonation damage occurs over and over until piston shatters or only rattles but then its to late.
If your coolant gauge is not pretty rock solid at 160, then you should investigate why.
The members boat that failed twice and then diagnosed the fuel pump caused the piston failure was incorrect. The pump may have been bad, and if so would need replaced.
I expect that if the engine failed twice, he backed of running the engine at full throttle after paying for two repairs. Unlikely restriction cured itself or technician cleaned it out during second repair.
I'm not god but I have 42 years as a professional technician, 26 years as a flat rate technician and 16 years as the factory service rep. for Toyota. I'm trying to help.

It's a bit dangerous to leave out there that a fuel pump failure would not cause that type of failure in a GT40 when it is a known issue that can and has caused failures -   Yes impellor debris also causes said failures, but in this case we already know that it happened again after an engine rebuild where presumably even if there were debris contributing the first time it would have been removed during the rebuild.   The reason the GT40s can fail this way when not too many other setups do has to due with the nature of the engine and its fuel injection system.   This was a fixed mapped tuned port setup – no feedback loop from an oxygen sensor to know if things were getting a bit lean and increase injector timing or back off ignition timing.   It was not the most conservative tune to begin with at high speed and if there was any failure that caused the fuel rail to have lower than nominal pressure then the engine would run leaner than the stock tune. Early fuel pumps had been known to lose pressure or fail slowly, later there were fuel control cell lines that could leak a bit back internally, and then there was whole lack of fuel control cell set of issues in the beginning.   Either way manifold pressure goes to about zero at wot, effective pressure the injector sees goes to low, engine goes lean but no oxygen sensor to increase fuel or kick out a dummy light so pistons get to hot and it was scuff city. It's a real thing, not only possible but it really happened to more than a few GT40s.    However I am not surprised even an experienced tech would not have run into that kind of failure as it wouldn't happen with most fuel injected engines.

8122pbrainard wrote: McCoy 1990 ski wrote: . I have never seen a fuel pump or injector cause a piston to fail Not trying to dispute the fuel pump being bad but if your damage was a piston, a fuel pump would no have cause that type of failure. JoeinNY wrote: It's a bit dangerous to leave out there that a fuel pump failure would not cause that type of failure in a GT40 when it is a known issue that can and has caused failures -   This was a fixed mapped tuned port setup – no feedback loop from an oxygen sensor to know if things were getting a bit lean Jeff, As a master technician with 42 years of experience, how much of it have you dealt with marine engines with fixed mapped injection?

Who cares Pete?

Probably more than you

With his experience I'm sure he would be a good addition to CCF, so stick around and participate Jeff

This whole conversation has me thinking back about 4 or 5 months when I first started tearing apart my engine, at first to merely swap the heads, and found what I thought was a nightmare:

Cylinder wall blockage

Still don't regret my decision to trash that rust infested anchor! Who knows if I could have ever gotten all that stuff out of there