What do you think of this cyl./piston??

[Summit8]

840 HO, probably 600 mi. max on topend, detonated a piston last season on mag side, bad gas or weather turned cold and was too lean when giving a ride in to a guy whos sled went down.

Tore top end down yesterday, rode a couple weeks ago in Big Horns, motor had a bad rattle, thought it was crank or rod bearing, crank was also replaced summer of 07. Was hoping not crank, turns out pto cyl. had 3 cracks on intake side and piston had deposited aluminum on cyl. wall, 2 spots with fine scoring of upper cyl. walls.

Attached 3 pics, cyl. pics are marked, red arrows to cracks, circled yellow where alum. is deposited on cyl. Top ring of mag. side piston has a spot were coating of ring is flaking off, wtf, cyl. looks good other than that.

PTO piston was causing engine noise I believe, was a lot of slop at the piston skirt, crank seemed tight.

What doo you guys think?? egts 1100-1150 top of pistons look plenty rich,running Phillips 66 Injex through injection,plenty of oil in crankcase and coating all parts, 14:1 RKT head.Riding at 8k+, prem. gas from Bear Lodge pumps.
Man I'm getting tired of this motor being down in the spring when I'm wanting to get out west a couple more times before the snow melts.

When I first checked comp., 155 on mag, 125 on pto, up on mtn, showed 125 each, but that might have been my tester. Dealer did first test with good tester.

 

[PJ-Hunter]

Kinda looks like my motor and that was an oiling issue. Just take the whole thing apart and check everything out. The dealer put a new top end on mine, but the damage was already done to the crank bearings. They were dry. 4 miles into the first warranty rebuild and the crank bearings came apart. Brand new short block from BRP. Motor was fine after that, until I hit a hidden boulder. Motor is still good, sled is trashed.

Some dude paid 4200 for it at a salvage auction.

 

[Summit8]

PJ- did that happen to your 09??

 

[PJ-Hunter]

PJ- did that happen to your 09??

Nope. The 08. Dealer thinks it was caused by the oil tank change. The original leaked so they put a new one in.

 

[Summit8]

What, no thoughts on this ??? motor doesn't have many hrs on it.

Faulty renic job? Crank going out again??

Not trying to bash BJ work, just want some opinions, wondering if I'm missing something.

 

[d&mraceengines]

well the problem with the cylinder is from the piston score looks like not enough oil to me do you burn atleast one quart of oil to 10 gallons of gas

 

[Summit8]

Close to a qt., oil pump cable was set to doo update spec for 02, they were way rich from factory, in fact the dealer set it for me on the mtn.

When i tore the top end off,(pto side scored), the mag side had a lot of oil pooled up around the crank, but there was still good oil film every where on the bad cyl. Rod bearing under piston was coated, top of piston and dome were coated. There was oil in both the oiler lines to the case.

Thanx for reply d&m.

 

[Red-eye]

If it was an oiling issue you would think both sides would suffer unless a hose came off or something. Did an 04 once that would do something simular. The rings would flake and the front of each piston would have crack across the skirts. Put new pistons in and run 1 gal. of VP 111 gas with 5 gal of prem. and never even had a mark since.( checked it twice cuz of 2 anti freeze leaks.) I figured it was detonation.

 

[Summit8]

Thanx for reply Red-Eye.

Yeah, since that detonated piston last spring that ended my season early, I've been thinking I should knock the comp down a notch.

The way refined fuels have gone this last year, might be a good idea to tune it down a bit, What we saw of diesel fuel quality this winter was pathetic, don't know if gas was same or not.

Good point,Thanx.

 

[Stanowski]

looks like a muffler bearing wore out and got into your cylinder and took out your piston return spring, causing your piston to do that

 

[Summit8]

Yeah, that's what I was looking for.

 

[DooUdew]

Looks like piston "wash" to me.. Sucked in some snow/water. It just happened to my 04' 800ho after a fresh rebuild. Buddy jetted me with snow from the side, blowing it by my prefilter and the engine took a fresh shot of snow just as i hammered it. The engine almost sized, but recovered, clattered and clanked the rest of the trip. When i got home and pulled it apart, it looked just like this.

 

[gus bohne]

snow injestion ..yes
lack of oil, NO way
wash on tops is typical, how does the exhaust EDGE of the dome look?
Is it rolled up and can you feel it when you run your finger across the dome?

If you can feel that the edge is rooled UP and see that the edge in front of the ex port is worn shiny then you have a clearence issue.
Exceesive clearance allows the piston to rock under load.
This is verified by wear at the exhaust edge of the dome and wear at the intake BOTTOm of the skirt. thrust loads cause these two locations to tell the tale.

If you had this issue it would make piston WEAR life short ( 780 srx big bores did this on the pto side). it was clearance and heat in that scenario.

I feel like that is a long shot, its more likely you got snow or ater in there.


Good Luck

Gus

 

[darocketman]

Looks like a cooling issue to me, popped two top ends the same way this winter. failure was at what I called the 4 corners on pistons and nicasil failure at lower part of cylinder in corners. piston speed drops at bottom of stroke which increases time in which heat transfer occurs between cylinder and piston. almost looks like what you would call a cold seize only lower on cyl wall. Cylinder support casting in in the 4 corners and that is what causes this failure. I drilled and tapped both water jackets on my cylinders and installed water temp gauges near the base gaskets temp would suddenly drop from 180 down to about 130 and then back up to about 210 in a couple seconds which indicated an air pocket in coolant system my fix for this was too fill with antifreeze and roll sled over, refill with coolant and do it again a couple of times untill all air is worked out of system the system ended up taking almost 1/2 gallon more coolant doing it this way!!! that is a ton of air in the system. the temp sensor on the head is decent but very slow responding and will not tell you if you have air in the system. one air pocket on a warmed up sled at WOT will eat a piston and nikasil plating in 1/2 mile run. your wash looks almost perfect and if oil consumption was low your carbon buildup on pistons would be much lighter tan. On a fresh rebuild I like to mix tank of gas 40:1 and run with oil injection hooked up. put a mark on tank and check to see if you are using adequate oil at next fill up if still quetionable keep running premix until you get an accurate reading on oil injection use amount. Your sled may want to foul plugs when running this extra plugs but atleast your engine should be safe so make sure to carry extra oil. I got so used to mixing when I did my last two rebuilds that I know have done away with the injection system and mix my own oil. I still have the tank on my sled with a petcock and hose coming off, I just throw a 20 oz bottle in my trunk that is marked for dif# of gallons of gas, I fill the sled up check the gals on the pump and then drain the corresponding ammount of oil into the fuel tank hit a few snowbanks to mix it up good and Im on my way. havent had any issues doing this now in the last 2600 miles and I know my engine is getting oil.

 

[darocketman]

also, look at ring gap position in proportion to scoring... Ive ran double ring pistons in my 700s with no major gains in performance of reliabilty except for the cost of pistons and rebuilds. ring gaps are one of the most common spots for failure since the hottest spot in the combustion chamber is at the ring tips and it gives two points insted of one for failure.. when the most common failures occur at the 4 corners and you are putting your 2nd most common point of failure (piston ring gaps) near these area it just seems ironic to add another ring and add even one more failure point... just my 2 cents. cracks at the bottom of piston skirts usually mean piston slap try to find 2 good spots on pistons to measure and a few good spots on cylinder to measure. a loose cylinder can cause wider ring gaps, more leak by and in turn more heat at the tips of rings. just remember you can get 150 lbs of compression with 1 ring and 150 lbs of compression with 2 rings but you are increasing your wear rate when you are running 2 rings... where is the performance gain in using 2 rings if you are not increasing the total compression of the engine?

 

[Summit8]

Hey rocketman thanks for the input, very good info.

d&mraceengines brought up the ? of wear at the top of the piston dome, if the edge was rolled over, I checked and it wasn't. Water ingestion could be a possibility from the looks of the piston I suppose, haven't really rode in alot of powder this season, all total 3.5 days of riding this winter.
Have had the airbox off a couple times before and during rides to adjust power-jets and not had any water trapped in airbox, spose it would be hard to catch.

As far as hot spots in cyl., my coolant was low the first day of our 2nd ride due to a loose hose clamp on coolant line under the bottle, caught it and topped it off because that's one of the things I always look at before a ride.Resevoir topped off and didn't have to be filled again and is still where I left it. Did some more looking at cyl. wall, is definetely a four corner seizure, real light on the exhaust side, intake side is seized right at the ring gaps like you said rocketmen. BJ uses these pistons to doo away with the poor piston design of the single rings, as I'm sure you know. I ran Wisecos before the 840HO topend with no problems whatsoever, dual ring of course.

It looks like this cyl. might be fine after cleaning the alum. off the walls, if not for the 3 cracks. After a close look, I don't think the nicasil is peeld, just alum. stuck to cyl. wall. It'd get a hyd. acid bath if not for those cracks at the bottom of the intake skirt, man those skirts are thin after boring these cyl.

Played around with the piston, sure is a lot of slop in cyl, even up above the ports where the cyl. is barely scored, the other cyl that was replaced before this short season is nice and tight. Well, just gonna have to box it up and get it over to BJ and see what he says, not looking forward to putting more $$$ into this motor.

Thanx much for the insight guys, some great points to remember, anybody else has anything to add, feel free.

Oh, and yeah I checked my muffler bearings and they looked like new yet, as did the piston spring.

 

[Red-eye]

I have seen bad and broken thermostats if you have one in there.This can allow for coolant to go in to the main coolers rather than recurculating in the engine first. ie. cold seisure.

 

[Red-eye]

I also had a thermostat fall apart into the water pump.

 

[Summit8]

It got a new thermostat on this motor build, but that doesn't mean anything. I'll look into that,thanx.

 

[bonecracker]

Just my opinion but I believe it's lack of oil. Just had it happen to me. 2 pistons before I realized that the oiler was working intermittant. The pistons will stick with close tolerance within 1 km of when it stops receiving oil. Everybody who looked at the pistons said cold seize. Too much "seize" on the intake compared to the exhaust, exactly like my new ashtrays.