Citroën BX – Cleaning the Engine and Gearbox

5 min read

With the Mi16 engine freed from the project Citroën BX shell, something became immediately apparent. It has not been especially well-loved, well certainly not in the sanitation area. It’s quite a surprise given how shiny the donor car, G-SEG, was. Time for some cleaning of the engine and gearbox.

How much cleaning does one gearbox need?

I’m used to working with diesel vehicles, car and plant, where oil leaks pick up filth, coating the engine black. But I’ve never seen a petrol engine this grotty. There simply isn’t a clean spot on the gearbox, from the clutch release arm to the gear linkage connectors, completely covered in oil.

The engine and gearbox in desperate need of a good cleaning
The engine and gearbox in desperate need of a good cleaning

Around the diff is by far the worst, and it’s clear how little mechanical love the donor car had. The drive shaft seals look like they could be original, they have certainly been leaking for some time. In fact, on the short shaft side of the diff, a CV boot has clearly let go and covered the box in CV grease.

Gearbox before cleaning, covered in heavy build up of grease and oil
Gearbox before cleaning, covered in heavy build up of grease and oil

With the gearbox disconnected from the engine, the inside of the bell housing isn’t looking too healthy either. It looks like the input shaft seal is original too, and it has been leaking as well. So step one of cleaning the gearbox will be to scrape off just as much as is possible. An entire take away box worth of road filth and oil removed with nothing more than a flat piece of metal.

Degreasing the gearbox

With the worst of the clag removed with a scraper, it was time to start really cleaning the gearbox. Starting with the application of a heavy-duty degreaser, a No-Nonsense variety from Screwfix. At £9 for 5 litres concentrate, it’s quite reasonably priced. I’m using this largely neat, however, the label on the bottle doesn’t state if it is aluminium friendly. The MSDS suggests it doesn’t contain Sodium Hydroxide which is the chemical that will corrode aluminium in non-safe degreasers

No Nonsense degreaser used in cleaning the gearbox
No Nonsense degreaser used in cleaning the gearbox

I’m using the biggest tray I have available, pouring some neat degreaser down one end then setting to work with all manner of soft and hard brushes. An old toothbrush is especially helpful here for getting up close to ribbing in the gearbox casing. I’ve started this degrease and cleaning process in the bell housing as it has by far the biggest build-up of dirt. It also lets me see what reaction the aluminium has to the degreaser in an area that’s not normally seen.

Rinsing off the gearbox

Every now and again I need to wash off the degreaser when it stops shifting the grime. For the gearbox I’m simply taking it outside and hosing it down, taking care not to get any water inside the gearbox or the dif. A few cycles of degreasing and rinsing and I’m done with cleaning the gearbox.

Cleaning of the gearbox bell housing complete

There is a balance to be struck while cleaning the engine and gearbox. It’s a 30-year-old car that I want to get back on the road and no matter what I do it will never be a concourse example. Well, it could be returned to factory condition with enough time and money, but that’s not what I’m trying to achieve. For me, cars should be driven and enjoyed, not polished and stored.

Exterior of the gearbox cleaned as much as is required.

That said, this engine and gearbox were so filthy they couldn’t be worked on. There is no point in fitting a new clutch or replacing seals around the head when they are only going to become contaminated. It’s also more pleasant to move and work on engine parts if they don’t stick to you and leave oil residue everywhere. There is a balance to be struck here. Spending time cleaning to be able to work on the engine and gearbox, without spending so much time the one year project grows into three!

Cleaning the engine

Cleaning the engine presented a slightly different challenge to the gearbox. There are a lot more hidden gaps on the engine, especially when all the ancillaries are connected. So the first step here was a partial strip down. The trick was to be able to access the head, block and sump without opening too many paths into the engine for degreaser and water to find their way in.

Front of the engine cleaned with degreaser and rinsed

The engine is also still swinging on the engine crane. This helps with getting the fluids to run off the engine, but creates something of a challenge for rinsing off the degreaser. In the end I used a high pressure plant sprayer filled with water to wash the degreaser off. It worked well, mostly, but a few days later I did find some salt build-up where not all the degreaser was washed off.

The back of the engine stripped and cleaned

Finishing off and sealing

As the rebuild of the engine continues, I’ll have the opportunity to continue cleaning some areas of the engine. I can give the block another going over once the sump and head are off. I can then coat the aluminium parts in engine wax to stop them from oxidising and going white. Fortunately, Comma does a spray-on engine wax which will make the job much easier.

I’ve found a number of issues with the engine, or at least it’s previous maintenance while pulling it apart for cleaning. I’ll wait for another article to discuss some of those, but I’m surprised this engine was running at all let alone with just 20ish horsepower missing!


NEXT – Mi16 engine strip
PREV – The Mi16 Engine Removal

Back to Citroen Articles
Back to Automotive Articles

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.