Compression Tester.

I am looking at getting a compression tester for my 2 1/4 petrol, which one would any of you recommend. Never used one before but they look pretty simple, dont want to get one that isn't half decent. So many on the market.

Any old cheapie will do for a petrol.
The values are interesting, but more important is that they are all as equal as possible.

Yeah, it's the doozel ones you need the high pressure stuff for. Saying that, I bought a cheap one off the bay that seems to work quite well.


https://www.ebay.co.uk/itm/132934958907

lynall said:

Any old cheapie will do for a petrol.
The values are interesting, but more important is that they are all as equal as possible.

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I am not 100% sure it is to do with compression, just eliminating things as I go,

jrose said:

I am not 100% sure it is to do with compression, just eliminating things as I go,

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Its one of them tools that rarely gets used these days, hence me saying get a cheapie, as there is a real possibility you may never use it again.

I have a couple of diesel ones, unlke petrol ones the diesel ones are a pita to set up and get a good seal for an accurate reading, I actually bought these 2nd hand for one job, and now they will sit in my garage for a decade or so!

lynall said:

Its one of them tools that rarely gets used these days, hence me saying get a cheapie, as there is a real possibility you may never use it again.

I have a couple of diesel ones, unlke petrol ones the diesel ones are a pita to set up and get a good seal for an accurate reading, I actually bought these 2nd hand for one job, and now they will sit in my garage for a decade or so!

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I have been working on engines of various kinds for over 40 years. I have never had a compression tester.
And if I remember correctly, have never used one either, although I could be wrong about that.

Turboman said:

I have been working on engines of various kinds for over 40 years. I have never had a compression tester.
And if I remember correctly, have never used one either, although I could be wrong about that.

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I bought them for a mates boat, literally never used one on a diesel before ever, or if I have I have forgotten! was actually quite hard finding one that would do the job, lots of crap out there.
VP TAMD31A starts/runs great/plenty of power really starts to pump vapour and oil out the breather canister as the revs and temps rise, he didnt notice until it had dumped so much oil in the bilge the oil pressure dropped!
I really dont want to do it, but I want the guy to build me a wall next year so am kind of committed!
Give it a ocuple of months until weather rubbish then we can start as he still wants to potter around in the boat in the mean time.

jrose said:

I am not 100% sure it is to do with compression, just eliminating things as I go,

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Try eliminating the thing that are common problems with those engines first.
Which would be ignition problems, often caused by faulty capacitors, coils, distributor caps.
Carburation issues, often caused by poor fuel, wrong carb or settings, poor quality fuel.
Timing problems, often caused by not altering the timing to cope with low octane petrol, or variable timing due to wear in the distributor drive train.
And make sure the valve clearances are right.

When you are sure all that is not causing your problem, might be worth removing the head, and lapping the valves a bit, and inspecting the piston crowns and bores. Wear in the bores serious enough to cause major compression loss will usually be obvious to visual inspection.

Removing the head will also give you a chance to look at the head gasket, and change it for a composite one if it is copper.

lynall said:

I bought them for a mates boat, literally never used one on a diesel before ever, or if I have I have forgotten! was actually quite hard finding one that would do the job, lots of crap out there.
VP TAMD31A starts/runs great/plenty of power really starts to pump vapour and oil out the breather canister as the revs and temps rise, he didnt notice until it had dumped so much oil in the bilge the oil pressure dropped!
I really dont want to do it, but I want the guy to build me a wall next year so am kind of committed!
Give it a ocuple of months until weather rubbish then we can start as he still wants to potter around in the boat in the mean time.

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That sounds like a pretty interesting one.

Not wishing to hijack the guys thread into another boat thread. Will just comment that I haven't known people have a lot of issues with those engines, they are generally well thought of.
But if it has raw water cooling, that would be my first port of call on a marine diesel that is overheating.

I've got a cheap draper one. Does the job just fine.
If you've got a starting handle, that'll give you an idea if you've got low compression on a cylinder or not