780srxgeorge
Member
to me it looks like the port timeing hole on piston is too large causing it to run a little lean? thats my 2cents.but all the other answers r someing too look in 2.good luck
very simple:
COLD seizure
Removing the thermostat is the most foolish thing you can do in a trail sled, these 780's use a wiseco piston which expands much quicker then the cylinder does, by making the engine take even longer to warm up, youd need to let that engine sit and idle for every bit of a half hour to put heat into the entire system to expand the cylinders at the same rate the piston expands,this is not going to happen in the real world, nobody is going to wait 30 mins or more to ride a sled everytime you run it!
put the thermostat back in!!, check the jetting as well because the wash is on the lean side and if you rattle these pistons in the bore, next youll break off the rear cylinder skirts as well.
carb settings:
jetting: 42.5-45 pilots
needles on the 4th groove with both shims on top of the clip
152.5 mains in all 3
93 octane fuel, not 91, not 87, if you cant run premium fuel and all you can get is 91 then you should at all times have 2 bottles of octane booster in trunk and add 1/2 bottle at every full fill up.
seeing how this engine was built for someone else and run for a couple years,then you bought it second hand,you wouldnt have had the warnings I tell all people about 780 engines when they want one built.(no fault of yours)
They run reliable and strong, but you have to let them warm up thoroughly and you need to run them rich enough to keep from detonating the pistons. There is no way around this using a wiseco piston. Theres lots and lots of my 780's out there and they run reliably and strong, but these warm up and fuel rules have to be followed or you will have problems,and its no differnt for any other maker of a 780 kit using a wiseco piston! 3 of the people here in this very thread have my 780 kits and they have all had the talk before the engines were built to make sure they understood the basic rules to having a 780.
For the future anyone buying a sled with a engine built by someone else should always contact the builder for basic carb specs and general information about what they have purchased, it saves alot of headaches in the future.
COLD seizure
Removing the thermostat is the most foolish thing you can do in a trail sled, these 780's use a wiseco piston which expands much quicker then the cylinder does, by making the engine take even longer to warm up, youd need to let that engine sit and idle for every bit of a half hour to put heat into the entire system to expand the cylinders at the same rate the piston expands,this is not going to happen in the real world, nobody is going to wait 30 mins or more to ride a sled everytime you run it!
put the thermostat back in!!, check the jetting as well because the wash is on the lean side and if you rattle these pistons in the bore, next youll break off the rear cylinder skirts as well.
carb settings:
jetting: 42.5-45 pilots
needles on the 4th groove with both shims on top of the clip
152.5 mains in all 3
93 octane fuel, not 91, not 87, if you cant run premium fuel and all you can get is 91 then you should at all times have 2 bottles of octane booster in trunk and add 1/2 bottle at every full fill up.
seeing how this engine was built for someone else and run for a couple years,then you bought it second hand,you wouldnt have had the warnings I tell all people about 780 engines when they want one built.(no fault of yours)
They run reliable and strong, but you have to let them warm up thoroughly and you need to run them rich enough to keep from detonating the pistons. There is no way around this using a wiseco piston. Theres lots and lots of my 780's out there and they run reliably and strong, but these warm up and fuel rules have to be followed or you will have problems,and its no differnt for any other maker of a 780 kit using a wiseco piston! 3 of the people here in this very thread have my 780 kits and they have all had the talk before the engines were built to make sure they understood the basic rules to having a 780.
For the future anyone buying a sled with a engine built by someone else should always contact the builder for basic carb specs and general information about what they have purchased, it saves alot of headaches in the future.
valin
Active member
mrviper700 said:very simple:
COLD seizure
Removing the thermostat is the most foolish thing you can do in a trail sled, these 780's use a wiseco piston which expands much quicker then the cylinder does, by making the engine take even longer to warm up, youd need to let that engine sit and idle for every bit of a half hour to put heat into the entire system to expand the cylinders at the same rate the piston expands,this is not going to happen in the real world, nobody is going to wait 30 mins or more to ride a sled everytime you run it!
put the thermostat back in!!, check the jetting as well because the wash is on the lean side and if you rattle these pistons in the bore, next youll break off the rear cylinder skirts as well.
carb settings:
jetting: 42.5-45 pilots
needles on the 4th groove with both shims on top of the clip
152.5 mains in all 3
93 octane fuel, not 91, not 87, if you cant run premium fuel and all you can get is 91 then you should at all times have 2 bottles of octane booster in trunk and add 1/2 bottle at every full fill up.
seeing how this engine was built for someone else and run for a couple years,then you bought it second hand,you wouldnt have had the warnings I tell all people about 780 engines when they want one built.(no fault of yours)
They run reliable and strong, but you have to let them warm up thoroughly and you need to run them rich enough to keep from detonating the pistons. There is no way around this using a wiseco piston. Theres lots and lots of my 780's out there and they run reliably and strong, but these warm up and fuel rules have to be followed or you will have problems,and its no differnt for any other maker of a 780 kit using a wiseco piston! 3 of the people here in this very thread have my 780 kits and they have all had the talk before the engines were built to make sure they understood the basic rules to having a 780.
For the future anyone buying a sled with a engine built by someone else should always contact the builder for basic carb specs and general information about what they have purchased, it saves alot of headaches in the future.
Well, that is one hell of a bold statement, and I tend to disagree 100% on this theory. There is absolutely nothing wrong with removing the thermostat. Sure it takes a bit longer to warm up the motor, but not excessively, and certainly not 30 minutes. This method ensures that the entire cooling system in the snowmobile is at a constant operating temperature, unlike what happens when the thermostat finally decides to open, and you get a wonderful cold rush of coolant flow into the motor. Sure, if you don't let it warm up sufficiently, you'll have issues with cold seizing the forged Wiseco's because they certainly do expand faster than cast OEM pistons.
9801srx
Member
sorry but i got to disagree 100% with you on that.sure that might be fine for a sled doing radar runs or groomed trail riding because your only cooling with the front and rear coolers pretty much so the coolant stays relativly hot but if you do mostly on off trail and powder riding with out a thermostat the running board coolers come more into effect when there burryed in powder and over cool the cylinders which will make the engine squeek.over cooling is more of a problem on a 780 than running a bit hot.valin said:
Valin, you can disagree all you want, its your opinion, but the result is this guys engine failure!
FYI: There is a bleed hole built right into a srx thermostat housing, along with properly aligning the hole in the thermostat passes little amounts of coolant ALL the time, its built there to remove air pockets but once the air is gone coolant replaces the void. So there is coolant moving thru there even at idle on a cold engine,no big rush of cold coolant hitting the engine because as designed, the thermostat opens slowly to prevent this big rush of coolant.
On a 780 trail sled, extended warm up time is already required, much more extended without a thermostat.....to the point of sillyness!
FYI: There is a bleed hole built right into a srx thermostat housing, along with properly aligning the hole in the thermostat passes little amounts of coolant ALL the time, its built there to remove air pockets but once the air is gone coolant replaces the void. So there is coolant moving thru there even at idle on a cold engine,no big rush of cold coolant hitting the engine because as designed, the thermostat opens slowly to prevent this big rush of coolant.
On a 780 trail sled, extended warm up time is already required, much more extended without a thermostat.....to the point of sillyness!
Tysonmatc2
New member
Viperking, part out the SRX, you just had your issue of which 3 sleds out of the 4 to keep solved......
no1chevyboy
New member
i would agree with viperkings assessment 100%
valin
Active member
This guys motor did not fail because he is not running a thermostat. The motor failed due to a lack of adequate warmup.
To the point of silliness? Have you actually attempted to do this? The time it takes to bring the water temperature up to 80 degrees or even 100 degrees is not "to the point of sillyness".
Removing the thermostat also helps to reduce the operating temperature, providing a proper drilled out plug is installed in the hose from the rail to the bottle to limit the amount of warm water that travels only throughout the engine loop. This also helps slightly with the warmup.
To the point of silliness? Have you actually attempted to do this? The time it takes to bring the water temperature up to 80 degrees or even 100 degrees is not "to the point of sillyness".
Removing the thermostat also helps to reduce the operating temperature, providing a proper drilled out plug is installed in the hose from the rail to the bottle to limit the amount of warm water that travels only throughout the engine loop. This also helps slightly with the warmup.
mopar1rules
Active member
i know my buddies '05 440 rev has no thermostat and my other buddy removed his thermostat on his '05 800 rev and neither have troubles w/warmup or cold piston siezures..... 
i know my banshee doesn't have a thermostat either.
i know my banshee doesn't have a thermostat either.
780srxgeorge
Member
hot
x2 on that.mine has had the thermostat in ti no promblem afther rebuild. i think about 5 yrs afther a good warmup.
To the point of silliness? Have you actually attempted to do this? The time it takes to bring the water temperature up to 80 degrees or even 100 degrees is not "to the point of sillyness".
Removing the thermostat also helps to reduce the operating temperature, providing a proper drilled out plug is installed in the hose from the rail to the bottle to limit the amount of warm water that travels only throughout the engine loop. This also helps slightly with the warmup.[/QUOTE]
x2 on that.mine has had the thermostat in ti no promblem afther rebuild. i think about 5 yrs afther a good warmup.
To the point of silliness? Have you actually attempted to do this? The time it takes to bring the water temperature up to 80 degrees or even 100 degrees is not "to the point of sillyness".
Removing the thermostat also helps to reduce the operating temperature, providing a proper drilled out plug is installed in the hose from the rail to the bottle to limit the amount of warm water that travels only throughout the engine loop. This also helps slightly with the warmup.[/QUOTE]
mopar1rules said:i know my buddies '05 440 rev has no thermostat and my other buddy removed his thermostat on his '05 800 rev and neither have troubles w/warmup or cold piston siezures.....
Do any of them use Wiseco's?
780srxgeorge
Member
thats what i got in mine with reast pins she runs STRONG! bout 2 weeks ago pulled the heads off & still looks good.
OZ_872
New member
I'm the guy with the '05 rev 800, i have RK tek FORGED pistons in my sled. Like Valin said, you have to put some sort of choke in one of the lines to allow proper circulation (can't remember which line). I have had zero trouble with the no thermostat set up... i usaully fire the sled up and let it warm up as i put my jacket, helmet and gloves on. by that time the rear cooler is usually already warm to the touch so I go SLOWLY for a little bit until im sure it has adequate heat. If you go on dootalk there are a few write ups about it and many many many people do this because you see lower temps with the engine which makes it less prone to over heat in marginal conditions. (and the doo T-stats are JUNK to boot!) once you have that mass of coolant warm it all of a sudden isn't going to just drop like 20 degrees, sure it will vary a bit but the combustion chamber and exhaust temp are going to remain consistant which is the most important part. Not to mention my built banshee with no thermostat and forged wiesco's, and all of the people who ride their dirt bikes (no T-stat) on the ice with forged wiesco's. Adequate warm up is key though!
viperking
Active member
Madmatt said:
i put 93 in it, ill check jet sizes when i get home sunday or monday
viperking
Active member
i didn't remove the thermostat, it was done by the previous owner, i let the sled warm up for a while but apparently not long enough, does anyone know where i can get 780 wiseco pistons for it?
Mopar had a set. Don't know if he got rid of them. Last I heard Wiseco was out of them. Some of the speed shops might have them. Hauck, Ulmer, Bender, etc...
no1chevyboy
New member
i would agree with those that have done the high perf mod, of removing the thermostat, but the important thing is to put the restriction in, or you will have problems, i have done this mod, not on a sled but if restriction is to much you will over heat from not enough flow and to little it will over heat from flowing through the coolers to fast and will take longer to warm up to temp. just from personal experience
OZ_872 said:
While I agree with most of what you say and I too had no issues with my Wiseco equipped monoblock XCR (t-statless system) . It was also equipped with a capilary temp gauge and I saw much larger than 20F degree temp swings. I could dive for powder and see 40-50 decrease instantly. In fact I'd always park in deep snow when stopping and watch the gauge drop 60+ degrees when restarting. I could feel the difference in drive away part throttle performance due to fat pilot settings to avoid idle hang. Depending on ambients, I'd "lean" things out a bit by parking in powder before impromtu drag races and as long as I wasn't stopped too long to overcool the pipes, it made for an arm streching difference. I actually retarded the timing 2 degrees to be safe with available trail-side fuel and could tune it with powder snow.
Point being that combustion temps were considerably cooler; enough to affect performance.
Recognizing the differences in the various systems including chrome vs. cast iron/overflow vs. degas, I have to imagine that my iron cylinders on the XCR held a bunch more heat than aluminum. Not enough to keep the same a/f ratio but it must have been enough to keep the cylinder from shrinking too much.
It kinda sounds like VK thinks warm up wasn't adequate so perhaps that was the root-cause so my addition to this discusion is somewhat moot.
However, the function of a t-stat (with bleed ball) is more than just a fixed orifice. It not only stops (nearly) all flow for warm up, but also varies flow based on temperature. It's actually quite fast when it comes to reacting to large swings in temperature and flow can be cut in half within a few seconds and visa versa. Whereas flow remains constant (at a fixed rpm) with a fixed orifice.
I would think an aluminum cylinder would shrink faster and further when subjected to the quenching affect of big temp changes so even though Valin and others have had no issue, is it because they haven't met the same conditions?
I have a great respect for both Don and Valin's knowledge and I'm not sure either of you are wrong. I'm just trying to learn from guys that live this stuff.
Mac
Member
bufalobob
Member
removal of the thermostat did not cause the engine failure. if anything it probably allowed it to live longer. the thermostat opens around 120 degrees in a cooling system that is designed for a 140 h.p.. you added about 20 h.p. w/ the 780 or in other words 14% more power. h.p. creates heat. removing the thermostat allows the coolant to immediately do it's job by wicking away heat via the heat exchangers without obstruction & well before 120 degrees. 2 cycles like hot pipes & cold motors. warm up w/out the tstat does not take much longer than w/it. take off your glove & feel the running board heat exchanger. if its warm your ready to go.
the pictures clearly illustrate the problem. no wash or in other words not enough fuel. mr.vipers main jet spec of 152.5 is clearly not in touch w/ reality considering the poor quality of today's pump gas. bender's trail port spec for a 700 srx w/ stock compression is 157.5 & that is not overly rich. on a trail motor you always jet for the worst possible conditions/fuel. when you pull up to the pump you may think your getting 93 octane but it could be 73 octane. no amount of octane booster is going to help w/ that & who wants to carry around bottles of octane booster anyway. if you had 2 jet sizes bigger than whatever you have in the carbs now this post would not be here.
btw valin is correct on the inline plug on a srx when you remove the tstat. my 194 h.p. bender 835 srx has 4000+ trail miles on it w/out a tstat. i plumbed in tunnel heat exchangers when i built it. it takes about 3 minutes to get the running board heat exchangers warm....not 30 minutes, which is absolute sillyness!!
the pictures clearly illustrate the problem. no wash or in other words not enough fuel. mr.vipers main jet spec of 152.5 is clearly not in touch w/ reality considering the poor quality of today's pump gas. bender's trail port spec for a 700 srx w/ stock compression is 157.5 & that is not overly rich. on a trail motor you always jet for the worst possible conditions/fuel. when you pull up to the pump you may think your getting 93 octane but it could be 73 octane. no amount of octane booster is going to help w/ that & who wants to carry around bottles of octane booster anyway. if you had 2 jet sizes bigger than whatever you have in the carbs now this post would not be here.
btw valin is correct on the inline plug on a srx when you remove the tstat. my 194 h.p. bender 835 srx has 4000+ trail miles on it w/out a tstat. i plumbed in tunnel heat exchangers when i built it. it takes about 3 minutes to get the running board heat exchangers warm....not 30 minutes, which is absolute sillyness!!