Engine Symptoms

[WFO Speedracer]

Glad to hear it maybe mow you will get some answers.

 

[E350]

See movie of piston wrist pin slop (very hard to see but I can feel it) here:

1994 Yamaha Super Jet 701 61x - video 3

You probably cannot see it, but I can feel it, there is up and down play on the wrist pin.s

rumble.com

Question: Can I just order

1. Two Piston Bearings;
2. Two Piston Pins;
3. Four Piston Pin Clips

And be good? Or are the above parts sold as a MATCHED SET with pistons?

Since my compression is good, should I replace rings or just leave the existing rings?

 

[WFO Speedracer]

they are defiantly not sold as a matched set , order , install and done, I would give it a hone and replace the rings minimum , you might want to go ahead and replace the crankshaft seals that way you can spin all the bearings by hand and know that they are good as well.

 

[E350]

I will replace crank seals. What honing tool would you recommend?

Replace with oem 81mm rings?

If compression was good at 160 psi per cylinder would you still hone and replace rings?

 

[fastgtfairlane]

Only real way to know if you need a bore is to measure your cylinder and pistons for wear. Otherwise you're ultimately guessing. If it were me and didn't have access to bore gauges then I'd replace the pistons and rings along with a light hone. But also keep in mind, when you hone the cylinder, you're still removing material.

I bought a kawi 750ssxi that didn't run for 150 bucks years ago, pulled the engine apart, I didn't have a way to measure the cylinders at the time so i put some new stock bore pistons in it along with new gaskets and seals. I got 2 seasons out of it all stock with a pipe out if it then decided to have the head milled and flywheel lightened. Got a daytona trip out of it and it let go at the lake flushing the salt out haha.

 

[E350]

Hmmm . . . I just watched this video:

If I hone it with a Flex Hone like in the video can I use 81mm rings again?

 

[kevbo]

The wrist pins should fit snugly when installed in the rods. It is very easy to check with the cyl removed. If there is excessive slack at the lower rod bearing then it’s junk. Look for corrosion, it’s easy to see on the sides of the crank. That is the main killer of cranks in a stock engine. While the engine is out, spin the driveshaft. It should be smooth and silent. It’s very common for mid shaft bearings to get wet and rust. If you hear a roar the bearing and seals must be replaced. Pump seals last longer but will eventually let water in and rust the bearings.

 

[WFO Speedracer]

You use the rings for whatever size bore you have, if it's 81.00 mm the use 81.00 mm , if it's 81.25mm then use 81.25 mm rings, the only time you use oversize rings is when you bore the cylinder to the next oversize , I will be very surprised if the wrist pin bearings are your issue , they rarely go out, I have only seen it a few times in over 30 years of wrenching on these engines , remove the piston , grab the rod and see if there is any up and downy play in the rod bearings , make sure you are applying pressure straight up and down , the side play in the rods is normal and it can be checked with a feeler gauge for excessive clearance , if there is up and down play in the rod bearing or excessive side clearance or it has noisy bearings when you spin them then the crank will have to be replaced .

One more thing while you have it apart have the cylinder taper and out of round checked, carry a piston with you when you take the cylinder to the machine shop so they can check the piston to wall clearance as well, just because it looks good doesn't mean it is good and no point in doing this job twice.

 

[Quinc]

For piece of mind and another 30 years of reliability you could rebuild it. Wait for the JM black friday sale and get an SBT crank, go up to pro-x 82mm pistons use kawa wrist pin bearings (gets rid of the washers) and be happy. =) If you sign up for the boyesen rider program you get 20 or 30% off on reeds. may as well rebuild the carb while your at it.

 

[Myself]

I have to agree with WFO on this one. I listened to the videos and that sounds like lower rod bearing slop to me........which is normally what goes first on a well used Yamaha 650/701. A light honing won't make much difference at all to the bore size. Best to measure it BUT....I have a hick backwoods test for you as well. Cut a strip of regular paper about 2 inches wide....make 3. Wrap it around a piston and trim the ends so the paper only wraps around one side of the piston NOT covering either wrist pin hole.
Place it into the top of the cylinder about 1/2" down. Put the piston dome side first (upside down) into the cylinder and slide it through. A fresh new bore and piston will slide through but feel snug. That's about 4 thou clearance. Stack a second piece of paper in and try again. A worn used but running engine will have the piston slide right through with ONE piece of paper but maybe even get stuck with TWO stacked in. If the piston will still slide freely through the bore with TWO sheets of paper stacked then it's likely OVER 8 thou clearance which is excessive and time for an overbore and new pistons. If you can stack THREE and STILL slide the piston through........you are on borrowed time and just begging to break a skirt and window the cases.

 

[E350]

I will do what you guys say. But here's some more local info.

This guy has apparently been doing jet ski engines for 30 years or so and is highly highly respected in the area. I will call him, but I have been warned by others who say that he is just slammed with business this time of year:



But there is a local general engineering shop which I have used over the years:




Langills is not an auto machine shop, it is CAD CNC but I have had them help me rebuild the distributor in my 1995 Bronco when the Hall Effect sensor failed and drill holes in my 7.3 PSD manifolds for dual EGT sensors and weld the bung on a new oil pan for the 7.3. They are very very precise.

I have the Yamaha Service Manual which specifies the tolerances on the crankshaft, etc. I think I will have Langills check the tolerances on the crank, pistons and piston wrist pins. cylinder roundness, etc. I get them, I respect them and I like working with them.

 

[Roseand]

I will do what you guys say. But here's some more local info.

This guy has apparently been doing jet ski engines for 30 years or so and is highly highly respected in the area. I will call him, but I have been warned by others who say that he is just slammed with business this time of year:

View attachment 451228

But there is a local general engineering shop which I have used over the years:

View attachment 451229


Langills is not an auto machine shop, it is CAD CNC but I have had them help me rebuild the distributor in my 1995 Bronco when the Hall Effect sensor failed and drill holes in my 7.3 PSD manifolds for dual EGT sensors and weld the bung on a new oil pan for the 7.3. They are very very precise.

I have the Yamaha Service Manual which specifies the tolerances on the crankshaft, etc. I think I will have Langills check the tolerances on the crank, pistons and piston wrist pins. cylinder roundness, etc. I get them, I respect them and I like working with them.

Send it to someone who specializes in two strokes. Also support those who support the sport. @Jr. Is more than capable to make sure your motor is good to go.

 

[E350]

Send it to someone who specializes in two strokes. Also support those who support the sport. @Jr. Is more than capable to make sure your moto

Jr is good to go.

Jr. is quite a ways away from the Sacramento Delta. Otherwise I would use him if he has time available.

I just checked with 2-stroke guru Meticulous Metal (Kelly), and plan to meet with him with the crankshaft and the wrist pins and pistons off this Wednesday !!!

For the Harry Eyeball evaluation.

He has been machining 2-strokes for near 40 years.

 

[WFO Speedracer]

I believe in supporting those that support the sport but at the same time I like to support local guys when I can, where I am at you can't because there aren't any , you are lucky you have someone reputable that is close enough to drive to , I will probably be using Paul instead of sending my stuff across the country , he is only a few hrs away..

 

[fastgtfairlane]

I have had nothing but top notch service from Paul. He's a great dude, knows his stuff, does excellent engine/tuning work and is someone I consider a friend. He's in GA and I'm in NC so about 5 hours. I also love that he is one of the very few engine guys that actually rides. I'll see him next weekend at a local ride next weekend. Before I met Paul, I had used Newmiller who is in Oregon. He was also a very very solid guy to work with. I heard he retired a few years ago. Believe it or not, you could easily put a cylinder and pistons in priority mail boxes and your engine ship cross country in 3 days.

There's also Erickson, I know most probably won't mention him but one of my good friends uses him exclusively and gets solid service from him. I think his only issue is the youtube channel probably generated more work for him than he could handle to meet their time expectations. I personally don't have any experience with him though. But my friends skis with Erickson built engines run pretty dang strong

 

[waxhead]

I have had nothing but top notch service from Paul. He's a great dude, knows his stuff, does excellent engine/tuning work and is someone I consider a friend. He's in GA and I'm in NC so about 5 hours. I also love that he is one of the very few engine guys that actually rides. I'll see him next weekend at a local ride next weekend. Before I met Paul, I had used Newmiller who is in Oregon. He was also a very very solid guy to work with. I heard he retired a few years ago. Believe it or not, you could easily put a cylinder and pistons in priority mail boxes and your engine ship cross country in 3 days.

There's also Erickson, I know most probably won't mention him but one of my good friends uses him exclusively and gets solid service from him. I think his only issue is the youtube channel probably generated more work for him than he could handle to meet their time expectations. I personally don't have any experience with him though. But my friends skis with Erickson built engines run pretty dang strong

Paul has been around for a long time and is known for great work.
Erickson has been around long before his youtube channel and I will leave it at that

 

[E350]

Put the Yamaha 650 in my wife's ski. It starts right up and spins the prop just fine on the stand.

Took her ski to the river and it would not spin the prop in the river.

I assume midshaft bearing?

 

[Myself]

A bearing would have to be locked up solid to NOT spin the impeller. Probably stripped splines in the mid shaft.

 

[WFO Speedracer]

Most likely stripped driveshaft and midshaft splines which would also explain the noise that you were hearing , they need to be replaced as a set

 

[DylanS]

The 650’s are notorious for stripping splines
with their insane arm yanking spine destroying career ending instant volcanic power generated mostly in part due to the comically small carb/intake setup that generates INSANE fuel/air velocity.
In fact I heard Yamaha actually had to detune them after the first 5 test pilots died instantly from the 15g’s of acceleration they put down lol.

sucks that the riding day was ruined but at least it seems you found your issue!!!