Scored piston

magoo · Jun 28, 2016

Newly rebuilt 1776 engine with 1600 miles on the clock loses all power on motorway. The engine has been stripped back to find a hole in the piston and light scoring on the rest of them. From what I understand this could have been caused by the carbs running rich, excess fuel washing away the oil. I'd like to avoid the same thing happening again and would like to know if this could be a result of bad machining during the rebuild or a badly set up engine?

Cheers.

StuF · Jun 28, 2016

What condition were the heads in on the side with the damaged piston?
Could be a symptom of poorly lapped inlet valves or sticky guides/spring allowing fuel to flood the piston?

Carbs could have caused it if they werent balanced correctly and one side was running much leaner than the other.
The leaner that side the hotter it will run

Any pics of engine/heads/piston?

magoo · Jun 28, 2016

It's possible that the carbs weren't set up right, I was a bit nervous getting it onto a rolling road so soon after the rebuild. I'll need to have a look with the rest of your questions.

Trikky2 · Jun 28, 2016

Lack of lubrication by fuel wash can cause scoring and pick up but looking at your photo it looks like overheating rather than fuel wash. Note the hole and the way the piston appears to crush the rings. Sign of detonation.

If your engine were pouring fuel into the cylinders enough to cause the damage shown, your mpg would have been below 10, your oil would reek of petrol and the oil level would be way too high (and would hence also have leaked severely).

The piston and rings look like they were running completely dry.

dustrat · Jun 28, 2016

I'm with Trikky on this one. Looks like a classic case of overheating. Did you have all the under engine deflector tin wear fitted ie deflector tin wear that fits between barrels and rear deflectors that fit on tin wear, crankshaft pulley end,beside no 2 and 4 barrels.If it had been a case of overfueling you would have had an increase in oil level due to fuel going in crankcase. Hope you solve the cause before you rebuild your engine.
Robert

magoo · Jul 25, 2016

Thought I would give you an update on this. We're not exactly sure of the cause because it might have been a few things.

Leaking aftermarket fuel pump, but managed to track down a NOS OG fuel pump, so hopefully that won't happen again. A loose dizzy, causing timing issues. The deck height on the engine rebuild was too low at 1.2mm. All appears to be well now with a new set of Mahle pistons.