Remove a stuck piston

 

Our new Daf 32 had a seized piston and, seeing as it's a topic that comes up often on various forums, I decided to note here how it was finally removed.  Note that this piston was seriously stuck, so the methods started gentle and got progressively more extreme.  The eventual winner was, as you'll see, pretty destructive.

The first step should always be to allow the piston to soak in something nce and penetrating, such as light oil or diesel.  In this case, because the engine is a flat twin, it meant removing the whole engine and propping it on it's side on the bench.  It was then left to soak for a couple of weeks:

Soaking piston

 

That made no difference.

So next we tried heat.  It's not easy to get a lot of heat into an aircooled barrel, but this seemed to do the trick:

Burning parafin in the bore

 

That's a bore full of parafin burning and it got the bore well up to "running" temperature, but failed to loosen the piston.

 

So we moved onto a puller.  That's pretty drastic because the only thing to pull against is the cooling fins, which are brittle cast iron:

Pulling barrel

 

No luck here either, and this had now been going on for about 6 weeks!

 

So it was time to use a bit of hydraulic persuasion.  Using an old spark-plug and some sticky-back plastic (well, metal tube really) I made an adapter to screw into the plug hole and attach a grease gun:

Dismantled spark plug

 

Grease gun adapter parts

 

Grease gun adapter fitted

 

Then fill the bore with oil (to save grease), reattach the head, and start pumping grease in:

Pumping grease into the bore

 

Using a spring balance and a bit of maths, I worked out that it got to about 800psi pressure inside before it finally moved - that's about 1.5 tonnes of pressure across the face of the piston.  Told you it was tight!

Only, it wasn't out yet!  After pumping it all the way to BDC, where the crank would stop it going any further, it was still stuck as far as any "normal" force was concerned.  So the crank case had to be split to allow the whole piston and crank assembly to move further.  It got as far as this before the oil started pumping past the rings and out the bottom of the bore.  Surely that must mean it's moving now?

Piston finally moved, but still stuck solid

 

No, it was still too tight to move without the haydraulic pressure!

So, at this point, all bets went out the window.  A club member has a spare barrel and piston available, and it was pretty clear that the existing one was going to be scrap.  So may as well make it completely scrap....

Cut barrel with angle grinder

 

Split barrel by wedging

 

Barrel split to end

 

Finally, disassembly can proceed!!!!

Barrel removed, piston ruined

 

Obviously, that last step is only acceptable if you have removable barrels and spares available.  If you don't then I'm afraid you're on your own.  But hopefully it won't come to that and one of the earlier methods will work for you before it gets that far.

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