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Discussion Starter #1
After a 500 mile trip and a hard pull back to the trailer my F7 engine was blowing white smoke and I could smell the antifreeze burning, but engine ran fine for the most part. New top end less around 1000 miles before. I replaced the o-rings with OEM but didn't find a break or damage on the old ones but the PTO side was washed clean. Started it up and at first thought it was fixed, but then put the coolant cap on and as it built pressure it started smoking the same as before. Looking for advice on what to do next? engine has about 6500 miles on it.

Looking for advice on what to do next - base gasket, water pump, cracked head/jug? No leak out the weep hole on the pump. One of the jugs was replaced when I did the top end. It seems to suck more coolant in on the stand when I rev it up then let off to idle - a big plume comes out. Definitely coolant burning, but the reservoir hardly goes down. Picture of head attached.

If it was the water pump, wouldn't it be on both sides and not just one? And isn't that what the weep hole is for, to keep it out of the crankcase?


 

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Discussion Starter #2
also - when I did the top end I replaced the PTO side cylinder with an exchanged replated one.
 

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How did you get all the antifreeze out of the base ? Maybe you are just blowing out and trying to burn what is still in there. By the looks of your head, it definitely is getting up to the top of your piston on the clean side. How long did you let it idle after you changed the seals ? Might take a while to get all of it out of the base. Keep an eye on the antifreeze bottle. That should give you some idea if it is still leaking or not.
 

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Discussion Starter #5
Thanks for the reply - I've run it through two heat cycles on the lift, less than 10 minutes each. Basically until the tunnel heat exchangers get warm. Could there be that much in the base? I thought that too - maybe coolant in the pipe and muffler still had to burn off. I marked my coolant bottle before I started so I can see if it's using it.

once I confirm it's taking it new, I was going to pressurize the system somehow and see if I can see it leaking into the PTO side from the head or cylinder.

If it was the water pump seal would it clean both sides?
 

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Discussion Starter #10
It's a sno pro 500 - I did the swap with an 04 F7 motor at the beginning of last season. I've put about 1000 miles on it - so far the engine has been rock solid.
 

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I have rebuilt many and never do it without changing the base gasket. If it's one cylinder its either a pinched o ring or base gasket. Also at 6500 miles you would be shocked at how bad the water pump shaft looks, we always change them if the motor is out, but you are saying it is only one cylinder. Antifreeze is very corrosive so don't let it sit to long like that without fixing it
 

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if it continues .....outer oring you will see coolant leak ...inner and compression will cause coolant to blow out thru coolant bottle overflow because of compression pressurizing the system ..i'd say a base gasket ...just my thoughts
 

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Discussion Starter #13
That is really helpful information - I was thinking that if it was just one side it wouldn't be the water pump. Next time I pull the engine I will rebuild the bottom end. I'm going to pressurize the system and pull the y-pipe and see if I can see anything from the head or cylinder walls, then pull the jug and change the base gasket. Thanks!
 

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Discussion Starter #14
if it continues .....outer oring you will see coolant leak ...inner and compression will cause coolant to blow out thru coolant bottle overflow because of compression pressurizing the system ..i'd say a base gasket ...just my thoughts
That makes sense - hadn't thought of that. Nothing coming back into the coolant bottle and it is defiantly slowly going down after running - maybe 1/8" after 20 min.
 

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Discussion Starter #15
Pulled head again and removed cylinder on the washed side. Does this look to you like the one side (right in the picture) wasn't sealed properly? The cylinder had a slight rock to it when I removed the bolts. Going to replace and check the dowels.
 

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At first I thought yes but now looking closer...I'm not sure. I'd pull other cyl and replace with a factory cat gasket though, not whatever that one is.
 

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Discussion Starter #18
I think I found the problem - one of the locating dowels was not seated properly in the cylinder. Difference was slight (.186 vs. .133) overall height of pin above surface, but enough. Putting back together now with OEM gaskets.
 

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You think the cylinder as being held "up" by the dowel? Sounds possible, but I would have said unlikely. Lets hope it's the case here. I had a buddy that put a sled together once with -no- dowels, on accident. Never noticed it. It an great for 3 years until I had it apart for an unrelated issue. Cyliders lifted off Really easy.,
 

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Discussion Starter #20 (Edited)
You think the cylinder as being held "up" by the dowel? Sounds possible, but I would have said unlikely. Lets hope it's the case here. I had a buddy that put a sled together once with -no- dowels, on accident. Never noticed it. It an great for 3 years until I had it apart for an unrelated issue. Cyliders lifted off Really easy.,

I think it was - I put the dowels in the crankcase first and put the cylinder down on them; one of the dowels cocked slightly. The dowel in question was locked tight with a gap at the upper end of the hole in the cylinder side. I cleaned the holes and tapped the dowels in that side first - they went in way further, all the way to the shoulder of the hole. I questioned it when I put it together; should have pulled it and figured out what was wrong. It didn't sit quite right but it was so close.
 
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