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F7 Seizure Diagnosis

3K views 13 replies 3 participants last post by  2003F7CAT 
#1 ·
Ok engine experts, my engine locked up on a ride this season. It was a very cold day so we let them warm up for 5-10 minutes, locked up less than a mile down the road. I didn’t touch the exchangers before taking off but after it seized I felt them and they were ice cold. So it makes me think I had an air lock or leak of some sort?

Well I just started tearing into it today so hopefully you can help me diagnose the piston seizure. Only mag side is toast. Also do you think I should get a reman cylinder or is this one salvageable? Replace both pistons or one?

The seizure marks are on the front and rear of the piston... mostly on the exhaust port side.(front)

Here are the pictures.
 

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#2 ·
Mag cylinder only?

Rule #1 of the “reverse coolant flow” system of the lay down series engines: ALWAYS allow full complete warmup time. Until BOTH outer foot rails of the tunnel are very warm to the touch. Usually a solid 8-10 minutes of idle time only, BEFORE even thinking of taking off. The colder the weather, the longer.

THEN, during the first 1-2 miles of riding, go at a moderate pace, while snow begins to coat everything related to cooling system, this will “stabilize” components throughout the system as things become closer to the same levels of temps related to normal operating temps, avoiding “thermal shock” (where colder coolant enters the engines cylinder head first), often leading to tops of pistons beginning to seize as heat soaked cylinders will rapidly begin cooling off (shrinking bore diameters), making the heat soaked pistons begin contacting with very little (to negative) clearances and leading to damage that happens “mostly” 180* across the respective pistons dome from each spot (like your piston/cylinder show here)

Traditional coolant systems flow coolants through lower end of engine first, allowing the engines lower cases and internals warm it up a bit, making any kind of thermal shock “nearly” improbable, unless the rider is a real fool and just keeps it pinned until complete lockup occurs. Then, you’ll have a smaller form of it at tops, but mostly at mid-height of skirts.

Now, if only your mag side is damaged, chances are that it wasn’t Thermal shock” that caused this. Reason...? Because the cyl head’s inlet nozzle tends to make the PTO side lockup first (due to flow already having a pattern of momentum favoring more coolant flowing to that particular cylinder as it enters the head itself through the angled inlet), weird, I know, but I’ve seen this for years now on the lay down engines, often more than once with a few folks who wouldn’t listen and follow warmup procedures properly.

Check for rotted or torn intake flange(s), also look at the flywheel and see if it exhibits any really notable oil streaks from oil being slung outwards from centrifugal forces while running (indicating a leaking MAG crank seal)

Search also for loose oil injection lines at the nozzles (could have sucked air, or not been adding as much line as needed (if loose enough) maybe missing clamps? Even on the pump nozzles (barbs) themselves?

But, most of all, please clarify for us as to whether or not the PTO cylinder and slug have any damage at all.
 
#3 ·
C-Note,

Thanks for the response, I will tell you this day that we rode was actually warmer than the previous days of -20F degrees that I had no issues with, and we allowed what i thought was ample time for idle warm up every single mornin. I am never hard on the sled within the first couple miles of riding to help prevent any issues like this. Not only that, there were other firecats riding with me the same morning, as soon as mine locked up I felt the heat exchangers of my buddy's F7 and his were nice and warm.

As I was taking the engine apart i definitely noticed the intake boots were starting to crack. I grabbed,bent, and twisted them aggressively and I was not able to detect a crack all the way though to the other side. So I don't believe this was the cause but I will be replacing these to prevent future issues.

I don't have any photos of the PTO side at the moment but when I get the chance I will upload a few of that piston and jug. To my eyes that side looks perfect.

I "think" that i'm planning on splitting the case completely so when I take the mag side off i'll see if i can detect any oil leakage around there. All the water hoses and oil lines were attached firmly to there proper locations. I've never done a case split so i'm a little nervous about sealing it back up, any recommendation for the case sealant?

Also do you think it's critical to have the crankshaft checked and trued? or should i just resemble? I'm hoping to find a cause of the issue before starting the assembly process and it's always nerve wracking on the first startup of a rebuilt engine to wait for the heat exchangers to warm up. C-Note, honest opinion of running SPI pistons vs OEM for the F7? SPI are about half the cost so it's temping to run those.

Thanks
 
#4 ·
Never accused you of not full warming up (or being hard on it)

Was only stating (and explaining) my #1 rule for cold starting/warming up one of the lay down series engines.

It PTO side looks good (so far), and your one photo above shows ample oil on each crank cheek (light reflecting back), then I’m wondering if maybe a foreign object somehow made its way into that cylinder (maybe a broken reed?), or perhaps a chunk of ice somehow made its way and wound up in that throttle body (supplying water, and beginning to lightly seize the intake side), forcing exh skirt forwards into contact with hotter cylinder surface (near exh port)...?

Really hard to say at this point....

THREE-BOND 1184 engine sealant (same company that makes Yamabond and Hondabond and Suzuki/Kawasakibond)

SPI pistons, I’ve sold for decades at various establishments, under the brand name: Namura even, they’ve never failed a single person yet that has had decent cylinders to utilize.

They come in a special casting method for bigger cc engines (including the F7’s), makes the skirts more durable (similar to genuine oem Cat pistons)

Get those, you’ll be just fine with them. Like I said, over the past 3 decades alone, I’ll put serious $$ on the fact that I myself, have sold well in excess of a 1,000 SPI’s (older ones, and special spin cast ones) with no issues. I don’t care what anyone says, they’re a great piston.

If you’d like another longtime machinists opinion, I can provide a link to his website so you can contact him direct. Fact is, he’s bought close to 1/3 to 1/2 of those very pistons I mentioned above. (“Irondog”)

Again, ONLY failures I’ve seen, were cylinders (iron bore) needing serious bore resizing to true them up, or to rid them of serious previous piston/dirt damage (grooved badly), and nicasil bores that needed replating.
Those are due to folks who were “cheaping out”.

You have my word on that.
 

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#6 ·
Sorry C-Note that wasn't supposed to come of as defensive, I know without face to face contact it's hard to interpret a tone with only text. So no worries definitely appreciate the advice your giving.

So I took the other cylinder off the PTO side as well now, and I didn't notice any damage at first but after a little closer inspection it does look like maybe the piston and cylinder rubbed a slight bit and almost seems like a hairline crack in the piston. Not sure if you'll be able to see it very in the images.

Do you think either of these cylinders should be reused or should I get two replated cylinders? I've always been one to go with OEM parts but with the cost difference and what I've been hearing I think I'm going to give SPI a shot.

Do you think this is more likely that there was somehow an airlock in my coolant line, or even possible that it froze up somehow even though it was colder nights before when it was fine. I would hate put this back together without really figuring out what caused this to happen. Do you have a place somewhere close to Ohio that does good crank work? Millenniium, Northern Crankshafts, BMP...ect?
 

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#7 ·
Never took as offensive, sorry if my explanation seemed that way. SPI’s are beyond a doubt, a great alternative to higher priced oem and Wiseco piston kits. Like I said (and I’m gonna pm You his number for crank servicing), Irondog (Jerry France) uses them in I’d bet over 90% of the sled engines (and ATV engines) where applicable... that’s testimony. As he does this for a living. I’ve known him since fall of 1984, worked for him for a couple years as well in my much younger technician days. Great guy to deal with. ??

I haven’t yet looked closely at latest pics (but I will), the mag cylinder, have that one replated at Millenium, make sure you have a piston assembly first though, ship it with cylinder, WITH recommended piston to wall clearances as well. They will finish the cylinder to within .0001” (1/10,000ths of an inch) of recommended clearances. But they need THE piston for that cylinder in particular, to do so.

The PTO, ship that with piston assy to Jerry (Irondog) along with your crank, jerry can use his diamond hone to true up any small deformities (if any exist), or clean walls properly and crosshatch it to the correct finish (he does all of this kind of work), I kind of egged him on to get started into it back when I worked for him, and when he retired from GM, he then began doing it full time as licensed DBA. He’s very reputable.

As far as ROOT CAUSE of ISSUE......? At this point, it could be anything. I’m beginning to think that MAYBE(??) coolant may have become either partially frozen (or clotted up) in the system, hampering flow? Maybe even bad thermostat?? Remove thermo from rear engine case and take to auto store, should be able to find lower cost match there.

And, I’d at least do a front heat exchanger flow test. It’s a great indicator as to how “healthy” your cooling system is.

Get 5-gal pail, bore hole in very bottom, add plastic inline hose fitting of same ID as the coolant hoses themselves, then a straight piece of same ID Hose to attach pail to exchanger. Pinch hose at closest point to Pail bottom as possible.
Fill pail to the 5-gal mark, using a timer, remove line pinch tool, time how long it takes to drain all 5-gallons, record this, repeat the fill and time procedure 2 more times. Add the times together, divide by 3 for AVG time flow.
Cat recommends no longer than 2 minutes and 45 seconds, and the closer to 2:20-2:30, the better.
If nothing else, this will not only test front exchangers flow rate, it will show if anything such as bad coolant or electrolysis (corrosion buildup) has hampered proper flow.

Flush rest of systems passages really well also. Looking for possible traces of evidence of any of that being clogged partially. In other words, if emitting very high volume of exiting water (showing what appears to be no flow restrictions along any of the way), you can rest assured cooling system will bleed properly when assembling back together (and not trap large pockets of air)

Replace both intakes that you mentioned seeing damage in. Check your reeds petals for damage to them, or the reed blocks seating surfaces (rubber missing, etc...)

Coolant wise, I do prefer a mixture of 60/40 (coolant/water), as this will do an even better job of resisting freezing once temps get (way down there!!), yet cools fine at normal operating temps. Why Cat hasn’t done this with their premix yet baffles me. Polaris does it with good results. Make sure you use coolant for aluminum engines and free of “pulp” contaminants (to avoid clotting)

When bleeding cooling system, the initial filling method does well, but I like to loosen coolant cap, warmup engine, then, using a flashlight to see bubbles that are in the system still, I remove hardware retaking coolant tank from fuel tank, position light UNDERNEATH the coolant tanks UPSIDE DOWN “T”, while watching for larger pockets of air as coolant flows (while occasionally blipping throttle to around 2800-3000 for a few seconds at a time, making coolant move faster to loosen up air pockets that may not be affected by idle speed coolant flow rates. As bubbles replace coolant from within the reservoir), keep adding enough coolant to keep from sucking in anymore air than what may already be in the system. (The reason I leave cap loose)

During the bubble searches, lift left ski into a milk crate for about 20-30 seconds, again, blipping throttle to loosen any air trapped, lower left ski, raise rear of sled off ground a solid 1’ - 1.5’, repeat throttle blipping while watching for excessive bubbles in upside down T at tank. Lower rear, raise rt ski and repeat again, also watching for bubbles of definitive size at the “T”. Remove crate from rt ski. Shut down sled, note coolant level in tank, allow to cool.. check cold coolant level versus hot, ideally, zero difference is the ultimate goal, but rarely does this occur. A variance of less than 3/8” is considered operable and ready to run, anything more than that, needs another bleeding session.

Ideally, IF one can position the coolant tank so that it’s “T” angles the flow direction “downwards” (by slightly tilting tank inwards towards chassis), the air will tend to have harder time BYPASSING the T, and taking nature’s course and going UP into the T instead of slipping past it.

That’s harder to do on the Firecats versus most any other sled of that era though. That’s why I recommend the milk crates and rear hoisting. When right ski is on crate, that alone forces collant to flow DOWNHILL, making air anti-gravitate back into reservoir.

Just be sure cold vs hot is 3/8” or less. You’ll be good.

There’s probably more that I can comment on, I do have some errands to run today though. I’ll be back later.
 
#8 ·
If you’re referring to hairline crack as being in photo 2, that’s a gouge from either dirt or a fragment of metal, more than likely whatever it was, became buried into the cylinders wall, as it didn’t travel past the top ring.
May have been a speck of hardened aluminum following initial smaller points of seizing?
 
#9 ·
In first series of pics the crank looks real 'dry' but in second series of the other cylinder the piston looks 'damp' As c-note said in his first post, check oil system for leaks, air or 'foreign objects' in lines. For the entire side of piston to be seized like that it looks like lubrication breakdown. Excess heat would be 'top down' 'cold seize' lower half of piston skirt. You did check fuel system ? Even slightest detonation could distort piston enough to cause that damage if several systems have slight problems. It's more difficult to diagnose several small problems than to spot a single obvious cause
 
#12 ·
Look closely at crank cheeks machines surfaces, the oil is there. The way the light reflects shows this.

We both have differing opinions on possible causes, and him saying his coolant rails were cold is what has me thinking it very well may have been air pocket (as the mag cylinder on these is the one that USUALLY survived a cold “thermal shock” from colder coolant hitting warmer cylinder), but, in this case, the cylinder that is USUALLY not prone to this, happens to be the one damaged (with me theorizing that it had some trapped air for some reason, while coolant was favorably “like usual”, flowing to PTO cyl)
I dunno

Not having it front and center leaves a lot of doors still closed. Know what I mean? ?
 
#10 ·
Thanks C-Note, hopefully I can get the case split this weekend and see how everything looks down there. I Saw your PM as well and appreciate you getting me that information.

As far as sending the cylinder to Millennium do I need to provide the recommend specs or should they have this already? I guess I should just call them...

I'm going to do your recommend procedures that you provided and hopefully the coolant flows well. The piston that I was questioning a crack would be picture 1 towards the top left of the piston. But at this point i'm not really worried about it because after I saw the scrapes i'm just going to do two new pistons.

Once I get this crank out i'll get into contact with Irondog.

I'm going to replace the intakes as well... I've read aftermarket are not the way to go for the boots... but at almost 1/4 of the cost are OEM worth it over SPI ones?

Thanks again C-Note
 
#11 ·
Jerry replied promptly earlier today to my text to him, he said he’ll hook you up. ?

Edit: I may have pushed things a bit in telling him you’d contact him as soon as I listed?
If you’re not yet ready, don’t worry about calling him at this time then. But, he will definitely take care of your service needs.
 

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#13 · (Edited)
I thought the 'white' spots were bits of piston, LOL :wink. Yep, I'm originally from Britain it rarely gets cold enough to freeze engines with antifreeze in them. I only ever saw it happen once, lower rad hose froze up while driving, ice plug stopped coolant flow and caused engine to overheat. 'We were pretty surprised as it was coldest winter on record at the time and a bear to figure out cause. Saying that, How old is the coolant and have you checked concentration? It could have been frozen in a small area when you started? it isn't something I have to worry about in central Florida as it rarely gets below 32f for more than a few hours. Altitude was something else I had to learn about, people living at 6,000ft or more have various other issues with non EFI vehicles
 
#14 ·
C-Note i appreciate you getting in contact with him so quickly for me. I wasn't able to get the crank bolt out on the magneto/flywheel this weekend. With the engine being out of the chassis i'm going to have to wait for a buddy to come over and hold the engine while I break the bolt lose... hopefully getting the flywheel to pop off wont be too difficult.

I guess I should go ahead and order pistons now too.

I will get a hold of Jerry and give him a heads up on whats going on.
 
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