just rebuilt powerhead, now change im compression

[TThornhill]

hey all. 1998 mercury 150hp 2 stroke carb. a few of u may know. just finished my power head rebuild and had a few issues on the water when i took it out. thought it was fuel so i replace the primer bulb. while i was working on it i figured i would check compression. they were all around 95 except for the cylinder that i fixed. it was at 65-70. it was around 90 fresh from the rebuild. i did notice that 2 of the reed valve lines had come off. but i re-attached them before i did my compression check....PLEASE let there be some answer besides "your motors screwed up". also it kinda, coughs, i guess you can say, every now and then.

 

[sschefer]

Re: just rebuilt powerhead, now change im compression

hey all. 1998 mercury 150hp 2 stroke carb. a few of u may know. just finished my power head rebuild and had a few issues on the water when i took it out. thought it was fuel so i replace the primer bulb. while i was working on it i figured i would check compression. they were all around 95 except for the cylinder that i fixed. it was at 65-70. it was around 90 fresh from the rebuild. i did notice that 2 of the reed valve lines had come off. but i re-attached them before i did my compression check....PLEASE let there be some answer besides "your motors screwed up". also it kinda, coughs, i guess you can say, every now and then.

Pull the head on the low cylinder side and have a look. 90 is low on fresh build if the cylinders were in spec and properly honed. They should have been around 100-105 and then come up to around 125 after breakin. 60-65 is a good indication that you broke a ring during the install. The cough and wheeze sounds like a bad seal at the case halves.

 

[TThornhill]

Re: just rebuilt powerhead, now change im compression

how long does it take for break-in, ive got maybe 2 hours on it

 

[sschefer]

Re: just rebuilt powerhead, now change im compression

10 hours is the recommended break in time. At no time should compression ever drop below what it was before it was first started. Don't doubt this and think the engine will get better at this point because it won't, I can guarantee that.

 

[TThornhill]

Re: just rebuilt powerhead, now change im compression

great, now i get to take it apart again. thats exactly what i wanted to do. well the ring didnt break during installation. cuz i cranked it up and ran it in the yard then checked compressions and it was at 95. once i took it on the water then came back and did it, thats when it was 65. i swear to god im gonna kick myself in the *** for using sierra rings if they broke. now im gonna go drink some beer.....

 

[westjr8]

Re: just rebuilt powerhead, now change im compression

Thornhill,
Please post the results of your find! I am currently rebuilding my powerhead too and would like to know what you end up finding! Thanks.