Reply
 
Thread Tools Search this Thread
 
Old 10 April 2015, 10:56   #1
Member
 
Country: UK - England
Town: Northampton
Make: RibTec
Length: 5m +
Engine: Outbaord mariner 75
Join Date: Apr 2011
Posts: 506
Compression?

Ok I have a 1991 Mariner 75hp 2 stroke and I just tested the compression and it appears to be 50psi across all the cylinders.

I warmed her up and pulled all 3 plugs opened the throttle all the way and cranked her over.
is this the correct way to do this and is 50psi low?
__________________

__________________
jezza2011 is offline   Reply With Quote
Old 10 April 2015, 11:36   #2
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,645
RIBase
If it's running, I'd suggest either your gauge or method of testing isn't right. It probably wouldn't even start at 50psi.

Did you carry on cranking til the gauge stopped rising?
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 10 April 2015, 11:38   #3
Member
 
Country: UK - England
Town: Northampton
Make: RibTec
Length: 5m +
Engine: Outbaord mariner 75
Join Date: Apr 2011
Posts: 506
Well that's what I was thinking.
yep cranked until it didn't go up any more.

it starts first crank
__________________
jezza2011 is offline   Reply With Quote
Old 10 April 2015, 11:39   #4
Member
 
Country: UK - Scotland
Town: Glasgow
Length: no boat
Join Date: Jan 2012
Posts: 5
if it runs good then i'd assume the gauge is faulty. you would normally be in the 120 ish range if my old 75 mariner is anything to go by.

on an engine i had once i did drop a cylinder down to 70psi and i lost about 15mph, you will know when you open it up if you really have 50 psi, i doubt it though.

cheers
__________________
nocando is offline   Reply With Quote
Old 10 April 2015, 12:31   #5
Member
 
Festinghouse's Avatar
 
Country: UK - England
Town: Chorley / Holyhead
Boat name: Northwind Challenger
Make: Tornado
Length: 6m +
Engine: Mariner 115 efi CT
MMSI: 235080598
Join Date: Jun 2011
Posts: 1,398
RIBase
Send a message via Skype™ to Festinghouse
yeah should be 120 on all 3 cylinders. have you done anything to this engine like a rebuild, or is it as is?
__________________
"Life may often suck, but the alternative is unacceptable"
MMSI Sticker

Member of S.A.B.S. (Lancashire Division)
Festinghouse is offline   Reply With Quote
Old 10 April 2015, 13:48   #6
Member
 
Country: UK - England
Town: Northampton
Make: RibTec
Length: 5m +
Engine: Outbaord mariner 75
Join Date: Apr 2011
Posts: 506
No its not had a rebuild. its just very old
still runs well
I will test the gauge
__________________
jezza2011 is offline   Reply With Quote
Old 10 April 2015, 14:50   #7
Member
 
dubrus's Avatar
 
Country: UK - Scotland
Town: Glasgow
Make: Ribcraft 6.8
Length: 6m +
Engine: Suzuki df200
Join Date: Jun 2010
Posts: 2,085
why did you test it?

i assume there is a reason, if it is down on power and you wanted to check then it could very well be correct.

cheers
__________________
dubrus is offline   Reply With Quote
Old 10 April 2015, 14:51   #8
Member
 
Country: UK - England
Town: bicester
Length: no boat
Engine: outboard only
Join Date: Feb 2009
Posts: 894
The correct way to do a compression test,
1/ power head as close to operating temprature as possible,
2/ remove all the spark plugs ,and connect the H.T. leades to a spark checker to earth them safely and not damage the stator,
3/ throttle wide open,
4/ Spin over on the starter untill the gauge needle stops,
6/ make sure you have a good battery.
__________________
uncle al is offline   Reply With Quote
Old 12 April 2015, 02:16   #9
Spammer
 
Country: Canada
Town: Southern Ontario
Boat name: -Unknown-
Make: SeaMax
Length: 4m +
Engine: Merc/Minn Kota
Join Date: Mar 2012
Posts: 216
Do a wet test. Remove all plugs, squirt a little oil in each hole. turn over a few cranks to spread the oil around the commpression rings. Put one pug in and do the test, note the reading. Remove plug and install other plug into other cylinder, repeat. If the difference between the dry and wet test is more that 10-15 lbs Ring problems. If the wet test shows a difference in reading of more that 12 lbs Ring problems. Rebuild in order.
__________________
Nightfisher is offline   Reply With Quote
Old 13 April 2015, 05:45   #10
Member
 
Country: UK - England
Town: Northampton
Make: RibTec
Length: 5m +
Engine: Outbaord mariner 75
Join Date: Apr 2011
Posts: 506
I am assuming the gauge is out. It starts and runs well.
Pulls well skiing and ringoing as well as hauling 6 divers and kit.
I was testing it to make sure its all ok as its very very old ( 1991)

I am fairly happy that its ok as like you guys say at 50psi I doubt it would start and run let alone pull well.
__________________

__________________
jezza2011 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 22:12.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.