Leak down Test

[spray25]

I was curious about my sled possibly being over full. I checked the oil (sled has not been started for about 3 weeks) and the oil was EXACTLY on the full line. I then started the motor and let it run for a minute and a half and checked the oil again. The level had went UP 1/4 of an inch.

Not what I was expecting.

Does anyone else want to repeat that little test?

 

[rxwarrior]

Oil Level

I have a fresh oil change on mine and will do the same test tomorrow and post the results.

 

[nhrxrider]

Its because of the dry sump system. The oil tank is high enough that when the sled has been sitting for a while, the oil can seep down to lower levels in the system. When the sled is started, the oil pump draws oil from those parts and raises the level in the tank. After it has been sitting a while the level goes back down. My stepson's Raptor is the same way, as was my old XR600 dirt bike. Both dry sump systems.

Jim

 

[nhrxrider]

The other thing I forgot to mention is that with the dry sump system, the oil level isn't as critical. As long as there is enough oil in the tank to keep the system from going dry, and enough air space in the top of the tank so there is expansion room for the oil, its fine. You can put in a larger tank for more oil capacity (helps keep it a little cooler) without a problem. There also isn't a problem with having the system a little bit over full, as long as its not too much so that there is not enough expansion room. The reason oil level is critical for a wet sump system is to make sure the oil level isn't high enough to come in contact with the crankshaft, which would aerate the oil.

 

[Buckeye]

I think there is plenty of pressure in the case. I have seen large globs of oil come out of my vent after some high speed runs and this is through the vent filter, which ia a K & N type. So there has to be some pressure to throw that oil out.
I broke my engine in according to Yamaha specs and had no problems until about 1200+ miles. Now at 3300 it is a quart every 200 miles.
I think the oil consumption is more prevalent than you may think. I know the turbo enhances the issue. I wish I had more time now to get into the motor, to see what is wrong in there. I know that mileage increases the chance of oil burning. It may be that alot of people with less than 1500 miles haven't crossed the threshhold of oil burning. It would be interesting to see the numbers on engines with over 1500 miles that have oil issues. I also believe low compression pistons reduce the risks. I think the combination of mileage, the turbo pressure and compression cause ring failure and then oil consumption.

 

[rxwarrior]

Oil Level

Before starting my sled today the oil level was on full on the dipstick. After running the sled for two minutes and shutting it back off the oil level was about 1/16" over full. not a lot of difference!

 

[nhrxrider]

I went out to the shoplast night to do a compression test, and I forgot one thing...the plugs in this engine have the very small thread size. I have a full set of good Snap-On compression gauges and none are the right thread. I did some checking and couldn't find a gauge that size offered anywhere...any thoughts where to get one?

Jim

 

[tundra]

Mine does like Spray. if the sled is parked and cold, i need to put 250ml of oil, and when she fired up, always overfill by 1/8 to 1/4. i had 5000 km on the motor,70 % off trail high reving burst, and 30 % of trail riding at high RPM.

i have only buy 2 liters of oil during my 5000 km. My friend Rx-1 mt do the same thing, and he ride like a . At the end of April, he did the ultimate idiot testing. 70km at between WOT and 9500 rpm. All of his lug took off. Only 8 lug was leaving on his track at the end. His Speed climb from 145 km/h to 170km/h at the end (nearly no lug remaining) Motor never heat, and put only 1/4L of oil. he was riding with CAT guy (F7)), who was unable to keep the pace, they are to scared of putting more than 1/2 miles at WOT .

 

[lakercr]

Pulled apart one of our motors that was a bit thirsty for oil. Motor has about 5000k on it, with the last 2500 being with a turbo. The pistons all had some blow by past the first ring. Cyl's #2,3 had blow by past the second ring as well. Carbon build up didn't appear to be a problem anywhere that I could see.

 

[spray25]

So after tearing down the motor what do you think is the cause of the blow by? To much crankcase pressure? Bad rings? Something else?

 

[lakercr]

The first step in trying to answer that question will be to carefully mic the entire engine and compare it to spec. I'll be starting on that today. End gap, bore symetry, etc. need to be checked first. I noticed that the end gaps on a few of the pistons were not where I expected them to be either when I pulled the pistons out. The core of the issue is ring seal, and I believe crank pressure to be a symptom, not a cause of the problem. This engine was broken in easy by Yamaha spec. - perhaps that wasn't the best method? If I had to guess right now, I'd say that the rings are failing because of one (or more) of the above, which creates excess crank pressure and the resulting oil consumption. I can't really add anything more meaningful to the thread until I'm done with the measurements...

 

[lakercr]

Got some of the measurements taken from the engine yesterday...

Ring end gaps (measured):

Cyl# 1st ring 2nd ring Oil

1 .020" .030" .025"
2 .024" .031" .024"
3 .024" .030" .025"
4 .024" .032" .026"

Yamaha Spec:

1st ring .010" - .020"
2nd ring .017" - .023"
Oil .004" - .014"

The top ring on cyl #1 is right at the outer limit of being in spec., otherwise, everything is out (oil rings WAY out) and would need to be replaced if I was putting these pistons back in (this motor is getting 10:1 pistons).

Piston skirts were within spec. on all four cyl. Haven't mic'd the bores yet, and probably won't get to until Wed. morning (the cyl's did still have the factory cross-hatch marks on them the length of the bore).

 

[spray25]

Yeah I would say that would definatly mean worn rings. So whats the cause? Poor quality rings?

How many hours do you figure this little project is going to take you?

Does anybody know what the going labor rate is for installing low compression pistons? I am just not sure I have the time or energy to do it.

 

[lakercr]

Good question... I'm going to have a chat with my dealer on this one.

The piston swap isn't that bad, even though I'm doing it by pulling the engine out of the sled. You can do this job with the motor still in the chassis which would save some time, but will still make a bit of a mess. I'd say that by the time the motor is back in the sled that I'll have about 10-12 hours into it. Try it, you'll like it.... :shock:

 

[spray25]

How do you do it with the motor in the sled? Can you remove the oil pan etc from underneath? I didn't think you could.

Which pistons are you putting in?