# Yamaha 50 compression questions.



## Brooksard (5 mo ago)

I’m on the cusp of purchasing a 2004 Yamaha 50TLR (2 stroke). The motor is extremely clean HOWEVER it has 90 PSI on all three cylinders. I would say I’m advanced as far has mechanic stuff goes, however this guy is a certified outboard mechanic. All of my experience with 2 stroke outboards has been that you want a range of 110-125 compression. He keeps assuring me that 90 is perfect for the Yamaha and I can’t find much literature on what it should be on the inter webs. Any help or experience would be greatly appreciated. Also, I’ve been on micro skiff for a long time but my last account was hacked and spam got posted on here so the account was locked haha. Glad to be back!


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## backcast (Apr 9, 2013)

My 2010 Yamaha 50TLR had 120 and up for each cyclinder.
Joe


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## Brooksard (5 mo ago)

backcast said:


> My 2010 Yamaha 50TLR had 120 and up for each cyclinder.
> Joe


Yeah that’s what I was thinking, 90 seems way to low to me


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## Sublime (Oct 9, 2015)

Try a different gauge maybe. You never know.


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## mwolaver (Feb 6, 2014)

So, I would think it is more important to have essentially the same readings across the cylinders. If 90 is a tad low, you still know you don't have a blown cylinder. Could mean high hours, but whatever it is, it's the "whole" engine. If it's really the right engine and the price is right....


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## bob_esper (Jun 3, 2021)

How long has the motor sat? and definitely try a different gauge. I have a cheap amazon gauge and it seems to read low all the time.


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## Brooksard (5 mo ago)

mwolaver said:


> So, I would think it is more important to have essentially the same readings across the cylinders. If 90 is a tad low, you still know you don't have a blown cylinder. Could mean high hours, but whatever it is, it's the "whole" engine. If it's really the right engine and the price is right....


I would say it’s the right price for sure, BUT I don’t want something I need to sink a ton of money in, in the future.


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## Brooksard (5 mo ago)

bob_esper said:


> How long has the motor sat? and definitely try a different gauge. I have a cheap amazon gauge and it seems to read low all the time.


Is a gauge really a “get what you pay for scenario”


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## Sublime (Oct 9, 2015)

Brooksard said:


> Is a gauge really a “get what you pay for scenario”


Maybe. You could buy a cheap one and if it reads 90 psi also, then you could assume the compression is 90. Call some friends and ask if anyone has one you can borrow.


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## Frank Ucci (Jan 20, 2019)

Is the motor running when you test or are you just turning it with the starter? If there is no two stroke oil in the cylinders to help seal up the rings it, might be causing your numbers to be on the low side.


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## TxSalt (11 mo ago)

Frank brings up a good point. You could fog the cylinders with 2cycle oil and retest.


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## Brooksard (5 mo ago)

Frank Ucci said:


> Is the motor running when you test or are you just turning it with the starter? If there is no two stroke oil in the cylinders to help seal up the rings it, might be causing your numbers to be on the low side.


Interesting idea, I hadn’t thought of this. This is just being turned with the starter. How exactly do you fog the cylinders?


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## Brooksard (5 mo ago)

TxSalt said:


> Frank brings up a good point. You could fog the cylinders with 2cycle oil and retest.


Good idea, how do you fog the cylinders?


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## TxSalt (11 mo ago)

I have used the Sta-Bil cylinder fogging oil when storing engines. That will work.


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## Smackdaddy53 (Dec 31, 2012)

Follow the Yamaha compression test procedure


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## devrep (Feb 22, 2009)

when you test with the throttle open it usually yields higher numbers. who did the test, you or the seller?


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## Brooksard (5 mo ago)

I watched the seller do the test, but I was looking at the gauge, and didn’t pay attention to see if he was holding the butterfly’s open


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## jonny (May 1, 2007)

Brooksard said:


> Is a gauge really a “get what you pay for scenario”


Yep
Cheap Chinese hose will swell absorbing some of the pressure. To me I always use a full metal gauge with no hose anywhere. Sometimes in cars you need a flexible hose to get in that rear cylinder tucked up underneath your dash.


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## Brooksard (5 mo ago)

jonny said:


> Yep
> Cheap Chinese hose will swell absorbing some of the pressure. To me I always use a full metal gauge with no hose anywhere. Sometimes in cars you need a flexible hose to get in that rear cylinder tucked up underneath your dash.


I saw the ones that go straight into the cylinder as well and liked that design


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## jonny (May 1, 2007)

Brooksard said:


> I watched the seller do the test, but I was looking at the gauge, and didn’t pay attention to see if he was holding the butterfly’s open


To get a accurate test the engine needs to at operating temp, all plugs out, fully charged battery, all leads ground and throttle wide open. You want it to spin as fast as possible to get the highest readings


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## jonny (May 1, 2007)

Brooksard said:


> Interesting idea, I hadn’t thought of this. This is just being turned with the starter. How exactly do you fog the cylinders?


I wouldn’t fog the engine for testing. There’s enough residual in there when warmed up for the brief spin over. Any oil added will help the rings seal. Giving you false better numbers


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## The Fin (Sep 28, 2021)

Sublime said:


> Maybe. You could buy a cheap one and if it reads 90 psi also, then you could assume the compression is 90. Call some friends and ask if anyone has one you can borrow.


Try Autozone for a free use!


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## Tarponhead (Mar 18, 2018)

jonny said:


> To get a accurate test the engine needs to at operating temp, all plugs out, fully charged battery, all leads ground and throttle wide open. You want it to spin as fast as possible to get the highest readings


Johnny isspot on, this is the standard for compression testing any engine. Follow these directions. Make sure the engine is at full temp. 
If a 2 stroke was properly maintained, and proper oil/mix was used, there should be almost no wear on the rings. For reference, My 2000 Evinrude 175 pump up to 105 psi on every cylinder, almost no variation. The engine has around 3000 hours. 
Dont forget, if the engine has not been decarbonized recently, the rings can get stuck in place in the piston groves, allowing blow by, and you will get lower numbers. 
If the numbers are all within a10% range, thats a good sign.
Good luck with it!


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## Brooksard (5 mo ago)

Tarponhead said:


> Johnny isspot on, this is the standard for compression testing any engine. Follow these directions. Make sure the engine is at full temp.
> If a 2 stroke was properly maintained, and proper oil/mix was used, there should be almost no wear on the rings. For reference, My 2000 Evinrude 175 pump up to 105 psi on every cylinder, almost no variation. The engine has around 3000 hours.
> Dont forget, if the engine has not been decarbonized recently, the rings can get stuck in place in the piston groves, allowing blow by, and you will get lower numbers.
> If the numbers are all within a10% range, thats a good sign.
> Good luck with it!


This makes sense! The motor was stone cold when we were turning it over and only the plug that we were testing was out. I may re-examine this option and see what the actual numbers are for this outboard


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## Tarponhead (Mar 18, 2018)

Let us know how it turns out.


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## Brooksard (5 mo ago)

Tarponhead said:


> Let us know how it turns out.


Well turns out the compression was still 88 to 90 psi on all cylinders so I walked, something didn’t seem right and I get spooky at a pushy seller! I’m still in the market though and this thread really helped!


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## Tarponhead (Mar 18, 2018)

IMO, probably the right thing then. 
Your buying the seller too when your purchasing something used, just like your buying the reputation of the company when you buy their new product.


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## bonitoman (May 20, 2021)

My 60 hp yamaha reads 125 on all 3 cylinders


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## MikeChamp12 (May 17, 2021)

I have the same motor. Mine reads 115 on all 3.


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