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kenward

sherco fan / heat problems ? ? ?

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i've just replaced both crank seals on my o8 sherco 290 because the gearcase seal was leaking and causing vast amounts of smoke whilst doing i also replaced the clutch and clutch basket . . . . . . .

after putting it all back together today went out to check all was ok

after riding for a couple hours i noticed it sounding diffrent (knocking) at the same time noticed the fan running constantly ???? let the bike cool down a bit and when restarted it sounded good again ( no knocking ) BUT . . . . the fan was still running ???

thought there might of been an air blockage, so went back to the van and checked the coolant level - all good

was concerned that i had'nt connected the water pump properly, so took thee water pump housing off , as i did also noticed the coolant wasnt that hot ( i could let the coolant run over my hands no problem )

moved the kickstart with my hands to check the impeller was workingand yep the impeller is all working fine.

refilled the rad with new coolant , started the bike , the fan wasnt on initially but after 2 mins or so it came on and stayed on, tried repeatedly squeezing the rad hoses whilst the bike was running but still the fan did not cut nor did seem to get any air out of the system , and then, the knock starts again !!! wtf !

was meant to be riding a trial tomorro - thats gone out the window now !! loaded the bike up and went home to check if there was anything on here . . . but there doesnt seem to be

any ideas help on this problem would be greatly appreciated,

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My Jarvis has a thermoswitch that every now & then will stick on causing the fan to run constantly, not really a problem as it just means the bike takes longer to warm up unlike if the switch doesn't work at all

I'd be more concerned with finding the cause of your knock

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hi mate , was goin on the theory that that the knocking was due to the bike becoming hot ??

i am new to trials and 2 stroke engines and cant really understand why the bike would get hot when it has fresh coolant, the impeller is turning and the fan, once started doesnt seem to stop running ??? and then in turn, the bike develop's a slight knock / rattle ??

strange ??? ? ? or am i missing something ??

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i've just replaced both crank seals on my o8 sherco 290 because the gearcase seal was leaking and causing vast amounts of smoke whilst doing i also replaced the clutch and clutch basket . . . . . . .

after putting it all back together today went out to check all was ok

after riding for a couple hours i noticed it sounding diffrent (knocking) at the same time noticed the fan running constantly ???? let the bike cool down a bit and when restarted it sounded good again ( no knocking ) BUT . . . . the fan was still running ???

thought there might of been an air blockage, so went back to the van and checked the coolant level - all good

was concerned that i had'nt connected the water pump properly, so took thee water pump housing off , as i did also noticed the coolant wasnt that hot ( i could let the coolant run over my hands no problem )

moved the kickstart with my hands to check the impeller was workingand yep the impeller is all working fine.

refilled the rad with new coolant , started the bike , the fan wasnt on initially but after 2 mins or so it came on and stayed on, tried repeatedly squeezing the rad hoses whilst the bike was running but still the fan did not cut nor did seem to get any air out of the system , and then, the knock starts again !!! wtf !

was meant to be riding a trial tomorro - thats gone out the window now !! loaded the bike up and went home to check if there was anything on here . . . but there doesnt seem to be

any ideas help on this problem would be greatly appreciated,

Hey Ken, Got your pm late, so figured I might as well post on here.

This does sound unusual, and everything you describe sounds as though coolant is not circulating.

Short of a pinched hose or blockage, seems you have checked the rest.

Two thoughts here, ok.

1- remove pump cover and actually start the bike briefly to insure the pump impeller keeps turning and there is no"lost cog" on the pump drive gear.

2- I have never tried this, but it seems somewhat logical to me that if in the process of doing your repairs you lost the thrust washer that goes on the pump shaft between the engine case and bearing, and the nylon drive gear, this could possibly cause or allow the shaft to move enogh to increase pump impeller to housing clearances to the point that it will not pump the coolant. IT IS EASY TO LOOSE THIS WASHER! So, I suppose one might even tell with the pump cover removed and if the impeller slides in and out too much, you may have found it!, now the wash!!!!???

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hi there cope , thanks very much your help . . . . . its much appreciated !

i am about to go and check ur diagnosis,it does sound like the only logical explanation :)

as far as the impeller moving in and out what is "too much" movement ??

would you recommend replacing the gearcase gasket again if i do have to re-build the water pump assembly, even though the current gasket has only been in the bike for two hours :(

will report back to you later on with hopefully a fixed bike :)

many thanks again , kenward

Edited by kenward

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hi there cope , thanks very much your help . . . . . its much appreciated !

i am about to go and check ur diagnosis,it does sound like the only logical explanation :)

as far as the impeller moving in and out what is "too much" movement ??

would you recommend replacing the gearcase gasket again if i do have to re-build the water pump assembly, even though the current gasket has only been in the bike for two hours :(

will report back to you later on with hopefully a fixed bike :)

many thanks again , kenward

I do not recall the impellers moving in and out at all, normally.

The gasket should be fine as long as it is not torn. :rolleyes:

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hi there cope , right after looking at the impeller as you said , the impeller has the slightest bit of movement ever ( maybe 1-2mm )

after re-filling the rad ( and squeezing the pipes to check for air , although i doubt very much if it possible to get an airlock within the system !

started the bike, but unusually took two or three kicks to start ? on the first and second there was HORRIBLE grinding / rattley noise like ends were shot !

started it anyway and the knock / rattle was not there, the fan cut in after just 2 mins and stayed on !!! let the bike run regardless , ( because it was not actually hot ! ) after 7-8 mins the bike was still not "hot" to touch . . . .the head was warm but not "hot" as you would expect . . . . . .took the thermostat out of a mates gasser that i'd been riding today :) and knew worked 110% put it in my bike and guess what . . . . the fan was not on when first started the , after around 5-6 minutes the the fan cut in and then cut after a few seconds !!! just how it always used to !!

sweet as !! new thermostat on order , 9am tomorrow ! :)

couldnt find any posts on here where the thermostat stays on permanently when its given up ?

now to sort the funny knocking / rattle noise that is most prominent when u kick it without HT cap on . . . . .. ??? any ideas

as always any suggestions greatly appreciated

many thanks, kenward

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Gotta admit I am not getting that warm fuzzy feeling about all this with all this mechanical noise going on, your measures on the pump impeller endplay, and what seems you may be a bit uncertain about that washer still yet by possibly NOT sticking it to the drive gear with grease so it does not fall off?

Thermo switch could be weak I suppose, but suddenly?

Other thing for knocking a lot would be possibly excess carbon buildup due to the original problem with the seals.

One thing for sure if that washer did fall off, it is likely to set caucht and do some damage somewhere.

You be the judge, I can only suppose! :rolleyes:

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Just to clarify does the washer go engine side or clutch cover side of the plastic gear?

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Just to clarify does the washer go engine side or clutch cover side of the plastic gear?

Engine side! There ia a good pic if you follow the

'pinned" service manuals link at the top of this forum and click the water pump seal replacement guide.

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hey there copemech , after ordering a new thermo switch yesterday , i have stripped down the gearcase side again today.

the washer you talk about on the water pump assembly is there :) (more luck than anything admittedly! )

but i have found found the clutch basket to be loose ! after checking the retaining nut and making sure that i had secured all the clutch basket rivets tightly i realised that its actually the clutch needle bearing which sits within the basket, that has excessive play ! so ordered a new one today, together with the top hat washer.

any ideas why the top hat washer is £55 !! and the needle bearing is just £16 ??? anyways , malcolm rathmell have said they doubt very much that i will need the top hat washer and if so , i can return it :)

thanks very much for your thoughts on this thread it is appreciated ! hopefully i will be able to put it down to a faulty thermo switch and a clutch needle bearing.

again many thanks copemech , will report back tomorro with hopefully a sweet sounding bike with a fan that cuts both in and out regularly !!

Edited by kenward

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hey there copemech , after ordering a new thermo switch yesterday , i have stripped down the gearcase side again today.

the washer you talk about on the water pump assembly is there :) (more luck than anything admittedly! )

but i have found found the clutch basket to be loose ! after checking the retaining nut and making sure that i had secured all the clutch basket rivets tightly i realised that its actually the clutch needle bearing which sits within the basket, that has excessive play ! so ordered a new one today, together with the top hat washer.

any ideas why the top hat washer is

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