98 MM 700 Engine Failure x2

[Rock Valley Rider]

Hey fella's,

I'm trying to figure out the problem to this sled, last season I had the whole motor rebuilt, crank trued to above factory specs. I ran pump gas with mineral oil mixed for the first tank and 50 miles on the trail during break-in this happens. I used SPI pistons and had the cylinders sent to Powerseal to get Nik'ed. As for the carb side I had a local shop do the adjustments. I told him that I normally ride from 4k to 9k typical Idaho mountains.

So here are some pictures of the devistation!

 

[Rock Valley Rider]

Part II

When I bought the sled used with 900 miles on original motor, I took it to Tom Hartman and had him set up the clutching and so forth...... Well anyways we were riding and the number three piston blew the skirting and cracked the lower crank case. So I sent if off to get fixed. Got all the parts in and rebuilt the motor and checked the compression and good to go. Then thats when hell broke loose. No more than 50 miles on the break-in and bam the motors goes again!!!!!!!
So please tell me what did I do wrong? I'm not an engine guy!!

 

[DOO800RIDER]

Something came apart or something foreign went through that engine! Did you do the disassebly? Were both wrist pin lock rings accounted for? The location of the gouging directly in line with the pin boss says to me that a snap ring came out. It's always difficult to diagnoss from pics....

What is the green stuff on top of the piston that looks like grass clippings? Was that there on disassebly,or are you working on this in a dirty environment?

Regardless it's toast at this point. With that much shrapnel going through the engine a complete dissasembly of the case halves is in order. One tiny peice of foreign material left behind could cause the same thing all over again!

If you are not an engine guy your best bet might be to look for a good used engine, and part out whats left of yours to recover some cost.

PM me if you have further Questions.
Brad

I ride a Full mod 99 MM myself. They are great sleds, but unless you want to ride it for years probaly not worth the expense of a factory remanufactured engine.

 

[TRIPLESWILLNEVERDIE!]

Was the circlip missing on the gouged up piston when you tore it down? As previously mentioned it looks very suspect. If it was still in place then it would seem one of the rings may have not been installed properly or the pin in one of the ring lands came out and caused a ring to rotate around till it hooked a port. I have seen that happen before on an old polaris triple that just had new aftermarket pistons installed.
Anyways your going to be splitting the cases and inspecting the crank. Crankcases can be welded but the crank is a little spendy so that would be your deciding factor as weather to fix what you have or buy a complete takeout engine.

 

[Rock Valley Rider]

After disassembling the motor I took a look at the pistons and all the circlips were in place and both ring pins were still in the pistons.

As for the grass on the piston, after I took them apart, one landed on my lawnmower hence all the grass clippings.

As for the head and jugs, do you think that it would be cost efficient to send them to PowerSeal and get welded and re Nik'ed?

Also I saw a craigs list add in Montana for a complete motor. If in fact I do purchase the motor, would it be better to have someone tear it down to make sure their is nothing wrong with it before I install it?

 

[nben]

whatever you end up doing, don't forget to make sure your pipes are clean!!! Any debris in there from previous failures can make it back into the cylinders and do it in all over again. I like to put a handful of bb's in the pipe and have a shake party after adding carb cleaner and taping the ends closed. Sometimes the hot aluminum can stick to the inside of the pipe and not come off until things get hot again.......

 

[Rock Valley Rider]

Thanks for the info NBEN!

 

[Rock Valley Rider]

Motor

If anyone knows of an available motor I can stick in this machine, let me know. The one on craigs list sold for dirt cheap! I went on totallyyamaha and I'm not too sure what motors I can use or even parts. There are alot of viper/sx/srx ect. ect.

Any information will be appreciated!!!

Thanks,

Danny

 

[M-Max]

You can use SX or a Mountain Max engine.

 

[DOO800RIDER]

Go back to TY forums, signup, and post a want to buy add. There are a number of sled bone yards in the midwest and back east. I have dealt with Central Snowmobile in Wisconsin in the past with good results. There's another in Vermont I've used but the name escapes me. Google Snowmobile wrecking yards. If you do rebuild your engine check your reeds closely. I have seen chipped reeds cause damage like that which is done to the piston crown & combustion chamber, But would not think it would cause the deep gouging to the piston skirt or bore.........

Almost forgot,I once bought a reman engine for a PooPoo from Central Snowmobile very reasonable. that engine is still running today.

 

[Rock Valley Rider]

Does anyone know if there is a good Yamaha motor guy here in the Boise area? I found the parts that I need and getting a good deal. I just want to make sure its put back together right and will be able to ride it a whole season!!!!!!

 

[sagerider]

Maybe call Tom Hartman (Hartman Inc) and see if he recommeds someone local.

 

[utah340six]

carbs

i would pull the cabs down and make syre waht jets the put in it ar correct.
before i started it again.
any one have 200 700 mm carb speck for him.
i had a turbo on my 2000 700 and none of my burn downs looked that bad.
as said some thing went trough your motor.
Bad.
could have started by lean condition or no oil.
then sh*t hit the fan

 

[Rock Valley Rider]

Ok I have found all the parts that I need to rebuild this beast!! Now all I need is some info from all of you for this rebuild. Everyone I talked to around the Boise area said they want nothing to do with this motor. The yammy dealers said around 3k + to rebuild it. I said no frickin way.

I just lost my job before Christmas so money is getting thin! Thank god for the wife the bread maker right now!!!

As for jetting and rebuilding I have a Clymers manual I purchased so please let me know if this is a good manual to follow! Also is it very hard to split the bottom and top end cases?

Them when I get everything separated what is the best cleaning method for the case and crank to get any debris off?

I will be doing this in my clean and heated three car garage!

So please any helpful hints would be great!!!!

And what is this trick I hear about adding string to the gaskets on the crankcase?

 

[Rock Valley Rider]

t t t

 

[X2Freeride]

What RPM range where you at when she went down? I would go through every one of my carbs all the way even pull the chokes out and apart. Check all your jets to make sure everything is clear and unobstructed. Check your oil pump to make sure its working. Then check your cables to make sure nothings broken or frayed and set up correctly. Make sure your timing is set correctly. Make sure your fuel lines and fuel pump is good. Even the lines in the tank. Drain your gas tank and start with fresh. This may sound meticulous be rebuilds are EXPENSIVE and preventative maintenance is much more prudent.

This should give you a good starting point.

 

[Rock Valley Rider]

I was only at about 5k when she blew, just on a trail leading to the hills.

Thank you for the information!!

 

[X2Freeride]

No problem. It may look like something got in their but if your mid range was too lean and it started detonating badly and a piece of the piston broke off which is pretty common it would look the exact same.

 

[shortman]

I would have to say that the rings broke on the one piston along with a midrange lean out. Guess better ask if the rings were still in one piece? I would for sure change the fuel pump, check your main jets and needle position,oiler cable adjustment(23 mm) and make sure the air box is clean.
My 2cents throw the mineral oil out and add 1- 2oz. yamalube to every gallon of gas in the tank.

 

[feeze]

I have been told to always use OEM pistons, ring, etc.. I have seen other people use the aftermarkets and have similar problems as you shortly after their rebuilds. I run 3 Yamaha triples (700mm, 600srx, 700MSRX) and have rebuilt all of them with OEM parts with no issues (touch wood). I have over 7000 miles on all 3.