Compression testing a compressor ?

[lexi]

I have put a new reed valve in my 3hp DD unit.

It will not fill the tank beyond 60psi and it will not cut off. I have checked and replaced all the other stuff or swopped with known good from another unit.

It just keeps running at the 60 psi. Before putting a reed valve in, it would only get to 45psi. I noticed the bores of the cylinders were very smooth.........no hone marks.

Ideas?

 

[jonjoe]

is it blowing air past the rings

 

[brightspark]

test with a compression tester take results then tip some oil in the bore on top of pistons if the pressure increases its the rings or bore at fault

 

[lexi]

I will try that.

Do you think it should have hone marks? They seem polished to me

 

[brightspark]

if the bore was worn there would be a lip on the top of it . more than likely be the rings if not

 

[normspanners]

Checked the pipe from head to check valve?

 

[kelsham]

I had a similiar problem with my compressor, I found the head gasket had blown. I made a new one and all was well.

Kels.

 

[lexi]

Thanks Kel.

I made a new one for one cylinder already.
I am looking for an adapter now to fit my tester as the two I have are metric.

 

[rtbcomp]

Can still you get spark-plug extenders? If so make an adapter by brazing a BSP fitting to one.

Or you could put a shot of oil into the inlet port and see if it reaches a higher tank pressure.

 

[lexi]

Ideas noted Roger

 

[brightspark]

putting a drop of oil in the inlet wont increase the tank pressure as the oil will blow through on the first few cranks . doing the compression test direct of the compressor outlet without oil and take readings . then with oil and take again will prove the wear on the rings or bore and will last a few turns before blowing oil out .