Boat shop says I need a rebuild, not sure to beleive them.

[gm280]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Actually the fuel mix fills in the two stroke engine both from vacuum AND pressure, but from different sections. As the piston goes down in the cylinder to release the burnt exhaust gases at the exhaust ports, pressure is built in the crankcase closing the reed valves for that cylinder section to force the mix into the cylinder as soon as the piston gets to the intake port openings. But as it does get to those intake port openings it continues traveling downward creating a vacuum to help pull in the fuel mix from both the downward travel of the piston but also the vacuum the exhaust gases create leaving the cylinder too. I don't know where the lower compression limit actually is for a good running OB...? I'd run it if it were me... JMHO! :joyous:

 

[daselbee]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Actually the fuel mix fills in the two stroke engine both from vacuum AND pressure, but from different sections. As the piston goes down in the cylinder to release the burnt exhaust gases at the exhaust ports, pressure is built in the crankcase closing the reed valves for that cylinder section to force the mix into the cylinder as soon as the piston gets to the intake port openings. But as it does get to those intake port openings it continues traveling downward creating a vacuum to help pull in the fuel mix from both the downward travel of the piston but also the vacuum the exhaust gases create leaving the cylinder too. I don't know where the lower compression limit actually is for a good running OB...? I'd run it if it were me... JMHO! :joyous:

Yeaah yeah yeah....so which is more important? Compression or vacuum? On the downstroke of course. I knew I would have someone chime in....Can't say a damn thing on here.....

Re: compression. The loopers have lower compressions. 100 psi or so. I look for 140 on a crossflow. It is hard to say, because OMC never posted any figures. All healthy crossflows I have worked on were up toward 130-140. But then again, they were prolly 1985 or earlier.

 

[brusk]

Re: Boat shop says I need a rebuild, not sure to beleive them.

How do you know if it's a Looper or Crossflow? 1989 XP150 2448 CC/149 ci. I can't seem to find anything on that or what compression should be.

 

[daselbee]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Well basically just by the 150 and 1989 that you posted.
But, technically, you look at the piston top, or you look at the block outside of each cylinder, or you look at the carbs....any number of ways.....

Piston tops have a huge dome or bulge on them. Loopers are generally flat tops.
Block outside of each cylinder will have a bypass cover installed. Loopers don't.
Most (not all) crossflows have one dual-throated carb that services two cylinders. Looper generally has one carb per cyl.

Look on shop.evinrude.com. Drill into your engine parts breakdown, and look closely at the cylinder and crankcase section. You will see reference #32 and 14 are the bypass covers.
You can see the domed piston a bit, in the crankshaft and piston section, not a good pic, but if you go to wiseco.com, they have good pics of their pistons. Blow the evinrude pics up a good bit to see better.

Just have to get familiar with them...the years, types, etc. Experience looking up parts and all that.....

 

[daselbee]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Here is a pic of a typical crossflow piston: Google Image Result for http://www.offshoremarineparts.com/images/uploads/All%2520images%2520on%2520site/3173ps_lg.jpg

Here is a pic of a typical looper piston: Google Image Result for http://www.happiemac.com/images/ebay/4320S_lg.jpg

 

[daselbee]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Ahhhhh...I guess 140 is a bit high as I posted above. I am searching, and I see 100s, 120s....so I guess in 1989, as the EPA got more and more involved...the crossflow compressions got lower.

As I said above. Whittle away at the peripheral stuff, and then if you just have to have it rebuilt, go for it.

 

[gm280]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Yeaah yeah yeah....so which is more important? Compression or vacuum? On the downstroke of course. I knew I would have someone chime in....Can't say a damn thing on here.....

Re: compression. The loopers have lower compressions. 100 psi or so. I look for 140 on a crossflow. It is hard to say, because OMC never posted any figures. All healthy crossflows I have worked on were up toward 130-140. But then again, they were prolly 1985 or earlier.

Sorry I have upset you. That sincerely was not my intention and therefore if I did offend you...my sincere apology. I was merely trying to explain to those that have no idea how a two cycle actually works nothing more... You seem very irritated and I’m sorry...

 

[daselbee]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Ah well....
I just didn't want to get into the vacuum aspect in a quick post to the OP....so I left it out.
I just think from a practical viewpoint, that it must be infinitely more "difficult" to create a positive pressure in the crankcase versus creating a vacuum in the crankcase through those big old 1.25" carb venturis and "flopping" reeds.
Hell, a human can suck such a vacuum with their own lung power. I doubt the same human could blow the crankcase up to pressure....
See what I mean? And since we were discussing rings and leakdown and therefore blowby....I only mentioned the pressure aspect.

I still think that if a service manager, who was a tech instructor, speaks of crankcase "vacuum" he is missing the main point.

Sorry for being touchy.

EDIT: All that above about human blowing and sucking is pure speculation on my part. NO s.e.x.u.a.l puns intended. But it seems that the crankcase pressure is more important to me. JMO.

 

[glenn property of pam]

Re: Boat shop says I need a rebuild, not sure to beleive them.

alot of people do not do a compression test correctly and the cheap gauges are a little fluffy on the numbers which is why its surgested to look at the diffrence between the numbers instead of the number. To be honest i may not be doing my test correctly myself. (if you do it wrong then do it wrong every time and compair the numbers)
The leak down is meant to be lower than 10% on a new motor but thats like saying the car with 100k miles is meant to test like a new car. Think of the motor this way its over 20 years old and its reached its half life. It will not give you 150hp and a new 150hp will kick your butt in a race (new is prop rated so a 130 would kick your butt anyway) so you have whats equal to a modern new 115hp motor so if you want to go boy racing then rebuild the motor if you want to go fishing where you will not be on the red line all the time then give it a tune up and fix the minor parts that fall off a 20 year old motor with the help of the old boys on here that cut there teeth on the old models and go have fun.

 

[jbjennings]

Re: Boat shop says I need a rebuild, not sure to beleive them.

alot of people do not do a compression test correctly and the cheap gauges are a little fluffy on the numbers which is why its surgested to look at the diffrence between the numbers instead of the number. To be honest i may not be doing my test correctly myself. (if you do it wrong then do it wrong every time and compair the numbers)
The leak down is meant to be lower than 10% on a new motor but thats like saying the car with 100k miles is meant to test like a new car. Think of the motor this way its over 20 years old and its reached its half life. It will not give you 150hp and a new 150hp will kick your butt in a race (new is prop rated so a 130 would kick your butt anyway) so you have whats equal to a modern new 115hp motor so if you want to go boy racing then rebuild the motor if you want to go fishing where you will not be on the red line all the time then give it a tune up and fix the minor parts that fall off a 20 year old motor with the help of the old boys on here that cut there teeth on the old models and go have fun.

Are you sure?? I was thinking that OMC's rating system changed between 1984 and 1986, making his '89 model 150hp equal to more recent ones.
JBJ

 

[clanton]

Re: Boat shop says I need a rebuild, not sure to beleive them.

It would help to know if engine is a GT johnson or a XP evinrude. These engines are not lacking in HP. You can take the intake port cover off and see if the rings are stuck, are lots of carbon on piston. With thses compression numbers, you should be putting your time on the ignition system and carbs. Timer base and stator is know problem these engines with 35 amp charging system.

 

[brusk]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Engine is an XP E150STLCEM. I just retested the compression numbers this morning since they de carbed the engine. Lowest is 103 and highest is 106 so it's a tad better and even more consistant across the board. I need to order a new timer base linkage and bushing as it looks like that's whats causing my linkage to fall off. I can't imagine you can have accurate timing with a bad bushing either.

Edit: Where do I even find this linkage and bushing?

 

[glenn property of pam]

Re: Boat shop says I need a rebuild, not sure to beleive them.

Evinrude Cylinder & Crankcase Parts for 1989 150hp E150STLCEM Outboard Motor