Compression guage

[Jup]

I've picked up one of those compression guages that screws in to the spark plug thread in the head.

Some of them can be very difficult to get to and I was thinking of making an extension bar about 150mm long, threaded etc, so I could get a spanner onto it.

Do I have to acount for extra air in the system for compression readings? Is there anything else I need to be aware of?

[gixkat]

some of those kits come with extended hoses so i cant see it being a problem

[ralph]

If you use the extension bar on all four pots, no probs. If you only use it on the inner pots I would assume your going to get a lower reading on the inner pots because air compresses.
Either way it would be easy to check how much your extension affects the measurement. Just check the same pot with and without extension

[Jup]

So if I understand you correctly, the concern is more of a comparison between each cylinder relative to the others - so it makes no difference as long as I check each one the same way?

[uncle pervy]

yep

[latheboy]

quote:Originally posted by ralph

I would assume your going to get a lower reading on the inner pots because air compresses.


Sorry but NO....
Pressure is Pressure
150mm of a Ø8mm hole wont make any measurable differance.

Make the thread about 5mm shorter than the spark plug and put an O-ring on the surface so it dont leak and give you a false reading

[scotty]

^^^^^^^
ya all good

[ralph]

Looks like you need to be aware of the number of responses your gonna get.
Latheboy, I only said I assume there is gonna be a measurable pressure difference however I did add that it would be easy to verify a difference.(if it exists)
By using the extension jup discribes I cant see how he is not increasing the capacity of the combustion chamber he is measuring, but then again it is fairly universal knowledge that Im just a dumb fucker anyway and really, really really I dont give a shit.
So, congradulations Jup, on your new aquasition, modify it so you can use it.

[latheboy]

ralph, your just a dumb fucker:D;)
nah your good, wasn't meaning to shoot you down bud.
Not going to get techinmacal here ..
Jup it'll be fine

[Jup]

Cheers for the responses fellas, if nothing else I got a chuckle :D

I'll add it to my bunch of custom bent spanners ;)