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Bristol 403 - Seized engine

Sitting around during the last winter my engine appears to have seized.

My Prestolite started doesn't engage very well but when it does it just stops.

What would be the best fluid to squirt down the cylinders, WD40 or and anti corrosion fluid like ACF50 to ease the seizure?


skidpan    on 20 March 2023

Surely you need to find a specialist on a valuable classic like this. Seizing over the winter suggests to me water has entered the bores, trying to turn it over could do serious damage.

edlithgow    on 27 November 2023

Depends whats stopping it. Get an endoscope and have a look, but I suppose its most likely to be corrosion at the rings which you wont be able to see.

Taking a cautious worst case view of the situation, you want an initial treatment that doesn't preclude a later treatment if it doesn't work, so I'd start with brake fluid which is water miscible, filling the cylinders. Leave to soak for say 12 hours, then syringe off any surplus and try to-and-froing it manually. Dont use the starter

I suppose its most likely to be corrosion, so white vinegar next, which will mix with the brake fluid, ditto

Perhaps follow up with another Brake fluid soak. Ditto. You could alternate these two treatments indefinitely but with diminishing probability of success.

Finally, if still no give, VERY HOT oil, maybe 2-stroke though it probably doesnt matter much what you use. ATF might be an option though I dunno how much heat it can take. If hot oil is too scary, just soak with ATF

Try not to burn yourself. Be especially aware of the danger of it spitting back out of the plug hole.

You could repeat this until you get bored or have a serious accident. The oil, once cooled, could be syringed off for a repeat but will quite quickly destroy the seal on your enema syringe

Once you've tried all that and failed, I suppose you'll either have to take the engine apart or get someone else to do it.

If you get any give work it manually until you can turn the engine over. If this is achieved, oil cylinders (if not already oiled) and change the sump oil, which will probably be contaminated, before trying to start the engine.

I suppose liquid nitrogen down the plug hole might be worth a try, and probably cheaper than specialist service. Needs careful handling though.

Edited by edlithgow on 27/11/2023 at 02:20

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