Yamaha SUV 1200 Compression

[mdilabs]

I have a Yamaha SUV 1200 and was going to check the compression. I went to the Service manual and it does not give the compression value spec. Does anyone know what it is on this craft?


BTW my compression is 100, 120,120 psi on cyl 1 ,2 &3

Thanks

[Technical Support]

Should be 120 in all, you have damage in #1.

[mdilabs]

Thanks - Thats what I was afraid of. I will take a look at the inside.

[mdilabs]

Took out the engine to investigate and on pulling the cylinder head I see damage in Cyl #1. Looks like an erosion at the edge of the piston between the piston top and the side. The erosion is right at the exhaust port and the spume from the erosiion is deposited in the muffler box right at the exhaust port. The opening of the exhaust port is also eroded at the top!

Also ther 3 cyllinder heads look different than each other. The have 3 differing degrees of carbon buildup/

This engine only has 225 hrs on it. It has been used for cruise riding. No hot dogging it. Is this 225 hrs normal time between engine services or is this a bit premature erosion and performance for an engine?

AK

[Technical Support]

That is detonation, from running lean. You will need at least a top-end job and to rebuild the carbs, plus check the fuel lines, fuel switch and tank for water/debris/clogs.

[mdilabs]

Thanks for the input. The engine has been worked before but not by me. It was dealer replaced (whatever that means)due to water injestion but I do not know what that "replacement" consisted of. Is there any way to tell if what is in the machine now is an engine that came from you guys. I did find some number markings on the crankshaft housing and the cylinderhead assembly. Do you guys stamp your replacement engines with some sort of SN?

If I do a rebuild, should I replace all the pistons or just the one. What about the piston Wrist pin bearings?

On the carbs - should I expect to do a rebuild every 300 hrs or so. That is what is on the carbs now.

Ak

[Ozpwc]

Re: Yamaha SUV 1200 Compression

Two of my mates had SUV1200 and both seized 4x on one ski, 2x on other.

I believe that these motors require some modification to the carbs to ensure reliable ops, however this mod also increases fuel consumption slightly.

My mates ski were not modified and so seized.!!!
Good luck.
ps post back if you can confirm above.

[mdilabs]

Re: Yamaha SUV 1200 Compression

Sorry to get back so late.

The only modification I made was to replace the choke with a primer.

I took off the head last week and it was ugly on that one cylinder. Man, I had no idea a machine could run with such a deformed upper ring. It was drooping down over the bottom of the ring groove. The cylinder exhaust port was dinged up where the ring hit against it.

The liquid oily residue ( 3-4 drops) in the bottom on the crankcase on this cylinder was dark - like soot.Things looked a bit heat stressed. In the other cylinders the residue it was a clear honey/brownish color.The film over the parts was more oily than in the cratered cylinder where things seemed drier with no residue. I guess the exhaust was getting a bit to the crank case and burning off the film.

[WATERCRAFTSERVICES]

Re: Yamaha SUV 1200 Compression

The Yamaha Non Pv 1200 Is One Of The Most Durable And Well Built Motors Ever Put In A Pwc. I Have Seen Upwards Of 1000 Hrs On Them Still Running. I Had 1 In The Shop A While Back With 1003 Hrs On It And The Problem Was A Broken Oil Line That Caused Damage To 1 Cylinder. Im Not Sure About The Previous Post Of 4 Seizures In 1 Ski But That Sounds To Me Like There Was Another Problem Causing The Multiple Seizures. I Have 2 Gp 1200 1 With 245 And One With 176 Hrs And Never Had A Major Issue With Either. If You Have 300 Hrs On The Carbs Go Ahead And Rebuild. They Are Due. If You Are Going To Repair Only The Damaged Cylinder Be Sure To Check The Clearances On The Other 2 And Also Closely Inspect The Rod Bearings While Your In There. It Is Not Recommended That Different Size Pistons Be Used Especially In 3 Cyl Motors. If You Dont Have Any Damage On The Other 2 Holes And Pistons Are Ok Resleeve The Damaged Cylinder And Go With A New Stock Piston. You Will Need Port Work Anyway If Your Intake Or Exhaust Port Sustained Damage From The Ring. You May Have A Detonation Problem Or Possibly Have A Ring Locating Pin That Came Out And Caused Your Problem. There Have Been A Few Posts On Here Recently That Have Had Locating Pin Failure On The 1200 Yamaha Motors. Not Very Common But It Does Happen.

[mdilabs]

Re: Yamaha SUV 1200 Compression

Thanks for the input. I have got an SBT engine on the way. I was going to do a rebuild but on thinking about things and how the hot exhaust might have damaged the crankseals or rod bearings, I decided I did not want to take the chance or the expense of changing out everything which would end up costing more. I find that repairing these things is a lot like remodeling a house, everytime you tear into something, you find sumpin else broken that needs fixing!

On that carb rebuild - Is there a kit I should ask for at the parts place or do I have to buy things one at a time.

Is a carb rebuild easy to do? Is there any link about how to properly rebuild a carb - or are there services that can do it that have the right equipment for testing it out before it is put on the engine?

[Technical Support]

Re: Yamaha SUV 1200 Compression

The Tech article section has carb rebuild guides, you need three Mikuni SBN kits. We also have videos in the video section.


Send your carbs to Carl at www.islandracing.net if you want them done.