Compression Test Numbers

[MaineBoy]

I just had a compression check done a 1998 Yamaha 175 TXR Salrwater Series.

It came back with the following cylinder readings

1. 120
2. 120
3. 120
4. 120
5. 115
6 120

I am told these are very strong numbers....just wanted to ask opinions from folks who know before I sign oin the dotted line. The engine is on a 1999 209 that I put a deposit on. Are these numbers as good as I think they are?

 

[Green Mountain Grady]

Hey Maine Boy,
I just went through a repower and spending way too much time looking at many different engines. I'm not a mechanic but those numbers look good. Every mechanic I did speak with said that as long as your results come back within a 10% range they're good. I've also had a few say 5%. To really make sure you could have them do a leak down test as part of the final acceptance.
Good luck and happy boating!

 

[Tashmoo]

What is the manufacturers range?

My 1995 200 HP salt water series ran at 115 - 125 which was in range for 12 years.


Make sure that the test was run hot with wide open throttle.

 

[enfish]

The numbers look good to me. Our 1995 175 SWS came in at all between 120 and 125 last time we checked.

 

[MaineBoy]

thanks for the replies. Looking forward to getting this baby out on the water!

 

[NOTHING ELSE MATTERS]

What is the manufacturers range?

My 1995 200 HP salt water series ran at 115 - 125 which was in range for 12 years.


Make sure that the test was run hot with wide open throttle.

How can you have a compression test at WOT ?

 

[NOTHING ELSE MATTERS]

FWIW, my 2000 150 Yammi had the exact same numbers when i did the test.

 

[jethro99]

What is the manufacturers range?

My 1995 200 HP salt water series ran at 115 - 125 which was in range for 12 years.


Make sure that the test was run hot with wide open throttle.

How can you have a compression test at WOT ?

You advance the throttle handle to the wide open position prior to doing the test.

 

[JUST-IN-TIME]

The right way to do compression checks ( different on 2 and 4 strokes also!)


all plugs out!!!!
safety lanyard pulled

Cold
Hot
Wet

2 strokes really do not need the throttle at WOT, its a 2 stroke!!! it still grabs air from the exhaust side

4 strokes i recommend a leak down test, not compression
you can still do a compression to get a OK reading