Low compression in cylinder 4

[joshmc]

First post here and looking for some advice.

Ive got at 86 T25 with DG engine. Its failed an MOT and needs a heap of welding, panels, sills, floor etc.

Before getting all that done, I thought id check out the engine (its driven great for me for last 5 years- up to scotland cornwall etc) to figure out what needs fixing first.

I just did a cold & warm compression test. Cylinder 4 was only 60 compared to the other 3 all around 130-135.

I feel its so strange that one cyclinder is so much lower when the others are all really consistent. Any advice on what to do/what could be causing this?

Ive read that drained hydraulic lifters could be causing it, worth adjusting those first? Or is it just an engine out job? Lastly while I'm doing these health checks anything else to look at?

I think an oil pressure test would make sense, as that could mean a bigger rebuild right? Looking for any words of advice. Sorry for all the questions

[davidoft1]

Has it had a good run recently?

[joshmc]

It has run fairly well, its a little ragged on start up but after a few minutes its smooth. Bit of whiteish smoke on startup too- not sure if thats a symptom.

Just trying to get a feel for the engine health before I chuck thousands into the welding!

[ajsimmo]

I think he meant has it been on a long run recently. Standing for a while can result in sub-optimal hydraulic lifter behaviour, possibly affecting compression. It needs a run of at least 45 mins of varying speeds to be sure the lifters have sorted themselves out. Then repeat compression test.

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[joshmc]

Ah ok interesting. Yeah it hasnt gone far recently, sat running for 20 on the road but will try taking it out for a good run. Appreciate the thoughts!