2 stroke to 4 stroke

[oldmako69]

https://www.amazon.com/Depstech-Semi...SIN=B06XRSRBZF

[99yam40]

Oh I found it it's a 93 not 92

always post the complete model # of the motor you are talking about.
that way we will know what motor it really is, not what you think it might be

[rodbolt17]

OMG
a car mokanic>
yas gotta be kidding me,
ya snatch off the power head. disassemble it.
figure out what parts are needed.
have the cylinders bored if needed reassemble and go play.
a 2cyl 2 stroke is about as basic as it gets.
I could prolly train a monkey to do it.
not nearly as complex as maybe an F250 or replacing the block and heads on an f350.
or even changing the shift shaft bushings o triple F350's.

[99yam40]

just for your info
OP I hope you also understand that the P in your model # says it is power tilt, and that it is not a power trim.
so it will not be able to trim up while under heavy power while in forward motion.

I also was a auto mechanic back in the younger days.
as long as you are mechanically inclined you should be able to work on it, but being as old as it is some bolts may not want to come out.
but it just takes your time to see if you can get it apart to fix it before you throw it away

Here is a parts break down for you motor here on this web site we are posting on
https://www.boats.net/catalog/yamaha...ar/1993/40plrr

[rodbolt17]

pretty much everything is avalible for that engine.
I happen to have a block downstairs that is already bored waiting for me to assemble.
dirt simple.
no valve train to muck with. no rod bolts.
simply place the rings on,use a dab of vasoline to hold them and drop the crank in place then line up the bearings to the block pins and roll.
no manufacture makes a kit. they simply do not know what you will need.
aftermarket kits are avalible for some motors but they may or may not contain all you will need.

[Tsgtwheeler]

Ok I have given this thing 6 doses of decarb. Inspection camera showed the top cylinder piston has some clean parts and bottom piston is still caked up. The cylinders board pretty much look the same nice and clean. No compression gain from bottom cylinder. Is there another way to clean the bottom better. Maybe it's not getting enough. Last night at 8 I let it run for 15min. The let it sit till 10 this morning before starting it smoked like crazy. But still caked up on bottom piston

[ausnoelm]

Why keep throwing cans of "stuff" at it? do the job properly and be done with it, it's a very simple engine, looking for the easy fix is not the way to go, run it like it is, or fix it, pretty simple really.

[DennisG01]

Have you gotten back on the water yet to try adjusting the carbs so it doesn't "fall flat on it's face" at high throttle application?

[holmen78]

I have a 90hp 2-stroke. My compression readings were all at 90 psi when they should be 125+ something when new. I opened up the head and measured the cylinders with a bore gauge. 2 cylinders were in spec (80.00-80.02mm). The bottom cylinder a little out of round probably because of a faulty lower crankshaft seal i found later. Took the engine apart and measured piston ring end gap and they were all beyond service limit by 0.05 mm. There were also soot in the ring grooves even though I had run ring free shock treatment. Otherwise the pistons were ok.

[rodbolt17]

whuuut????
where did you come up with the 125 psi?
if all were even at about 90 why in the ell would you disassemble it?

[holmen78]

The 125+psi was from memory, now that I checked it up from service manual it says 922kPa (133psi) when new. The compression number low in attached picture.

I disassembled it because It doesn’t start easy when cold, requires several tries with fast idle before it runs. Then it has to run at fast idle for at least a minute before it will stay running at idle. I wanted to find something that caused this. Carbs and all that easy stuff has been done several times before.

What I found was worn piston rings, a faulty lower crank shaft seal, 3 faulty check valves (those in the ends of the drain hoses on side of motor block).

Im hoping to solve the hard cold start issue and get a healthy new motor in the end.

[zenoahphobic]

The 125+psi was from memory, now that I checked it up from service manual it says 922kPa (133psi) when new. The compression number low in attached picture.

I disassembled it because It doesn’t start easy when cold, requires several tries with fast idle before it runs. Then it has to run at fast idle for at least a minute before it will stay running at idle. I wanted to find something that caused this. Carbs and all that easy stuff has been done several times before.

What I found was worn piston rings, a faulty lower crank shaft seal, 3 faulty check valves (those in the ends of the drain hoses on side of motor block).

Im hoping to solve the hard cold start issue and get a healthy new motor in the end.

Picture is not sharp enough to read anything.

This is probably an example where you have an engine that no doubt needs work done on it . So sometimes all amount of "fix it" fluids are a waste of time and money, when it is common sense to dismantle and overhaul wear and tear fundamental engine items, before it actually stops working.

[walleye1]

Every comp psi gauge reeds different, as long it's not to low and withen 15% between it is good.

[holmen78]

Now with the engine in pieces I know what those 4 “drain” hoses with check valves do. They feed the crankshaft bearings with lubrication.

Very few seems to know what they are and what they do. I have asked here before but didn’t get a qualified answer that I remember it.

A faulty check valve (like I had 3 of) must have some impact on bearing lubrication and crankcase pressure.