Banshee overheating

[grantevans713]

So I checked a few other posts but the recommendations won't quite help my unique situation. So I'll start by listing my bikes build.

It's a 421 with driveline cylinders, 68mm bore, long rod 4mil stroke, 24cc domes running 91pump, mikuni tm38s, shearer small bore in frames, oversized radiator, +6 timing.

I have my jetting spot on, I even just got a dynotune done by Nate at KAN powersports, it's pushing 98hp and 51ft lbs of torque. I did play with the netting a bit after the Dyno, but I've chopped my plugs and it's right where it needs to be, if not a little fat on the mains from trying to keep my temps down. 

I have opened my case and checked to make sure my impeller is functioning properly.

I have a MacDaddy inline cooler and tempguage, I am consistently overheating. I can't ride 10minutes WOT in a bowl without getting to 250 and stopping. About 20minites riding around the dunes without going above 3/4 throttle and I'm up to 230.

Im running amsoil dominator, 20oz per 5gallon, 91 pump ethanol free from its own handle so no starter trash gas. I am running engine ice in the oversized radiator.

So I am overheating a lot. Anyone have ideas? I can probably get some new domes for more squish clearance, would probably lower combustion temps. I could run more inline coolers but that seems redundant and like it wouldn't do enough.

Im running an OEM frame, has anyone setup a radiator fan that works somehow? Doesn't seem like much space, maybe smaller ones? Is there anything else someone has done? I really don't want to ditch the pipes and carbs for something else.

[diebog]

Hey on  the water pump are you running an oem one or billet aluminum? I replaced mine many many years ago with a billet and   from what i remember the billet one did flow more and cool it down slightly as I was having similar issues( but I could be wrong).  So I installed a billet impeller and got an oversized rad with engine ice.  On my 400 cub I run 18 cc domes and 110 race gas. Have you ever tried 110?  In some cases it can make the bike run cooler.  What ratio you mixing the gas?  I mix mine at 50:1 with Bel Ray H1R (best oil IMHO)

 I have the trail tech digital and a manual gauge inline so I can double check, are you 100%sure your gauge is good?.   Im not sure a fan will do much as a fan is more for when it’s idling or your going really slow and air flow past the radiator isn’t sufficient enough.  But If your cruising at a good speed your bike should be getting enough air.   Have you made sure there are no air bubbles in the coolant?  Can I assume the radiator is in good working order and not clogged?  Do you have an aftermarket grill?  I had one on my banshee and it was cutting off allot of flow.  If you have one you might one to try it without and see if there is any change. 
 

I’m no expert so just a few things I would check. 

[grantevans713]

On 7/31/2022 at 11:41 PM, diebog said:

Hey on  the water pump are you running an oem one or billet aluminum? I replaced mine many many years ago with a billet and   from what i remember the billet one did flow more and cool it down slightly as I was having similar issues( but I could be wrong).  So I installed a billet impeller and got an oversized rad with engine ice.  On my 400 cub I run 18 cc domes and 110 race gas. Have you ever tried 110?  In some cases it can make the bike run cooler.  What ratio you mixing the gas?  I mix mine at 50:1 with Bel Ray H1R (best oil IMHO)

 I have the trail tech digital and a manual gauge inline so I can double check, are you 100%sure your gauge is good?.   Im not sure a fan will do much as a fan is more for when it’s idling or your going really slow and air flow past the radiator isn’t sufficient enough.  But If your cruising at a good speed your bike should be getting enough air.   Have you made sure there are no air bubbles in the coolant?  Can I assume the radiator is in good working order and not clogged?  Do you have an aftermarket grill?  I had one on my banshee and it was cutting off allot of flow.  If you have one you might one to try it without and see if there is any change. 
 

I’m no expert so just a few things I would check. 

I have a billet impeller. I know if I change domes it will open up the squish clearance and lower combustion temps, but I wanted to run pump gas. The mix rate is above and is standard for banshees. The radiator is good, no air bubbles, the guage is right and I know it is overheating because it's spitting out antifreeze. I do have an aftermarket fullbore plastic and custom grill with more space to let air in, as well as an air scoop.

 

I think what I've decided to do is to run a second radiator under the seat. I can mount it low enough to get air, the extra coolant and space for airflow should cool the temps down. If that doesn't work I'll have to switch to 110 and 20cc domes

[dano3]

extra radiators, more inline coolers, those are all bandaids why not fix the actual cause. What is your static compression? what is the squish reading at on the outer edge and inner edge? Have you tried it at +4 timing? Where exactly is the temp gauge located at and have you verified it reads correctly- ie in boiling water? Have you tried a different radiator cap? the one on my ebay radiator was junk and switching to OEM stopped it from constantly venting. It will continue to spit out antifreeze if you keep adding anti freeze when it is cold as it is normalizing the coolant level for when it is hot. 

[grantevans713]

On 8/5/2022 at 12:56 PM, dano3 said:

extra radiators, more inline coolers, those are all bandaids why not fix the actual cause. What is your static compression? what is the squish reading at on the outer edge and inner edge? Have you tried it at +4 timing? Where exactly is the temp gauge located at and have you verified it reads correctly- ie in boiling water? Have you tried a different radiator cap? the one on my ebay radiator was junk and switching to OEM stopped it from constantly venting. It will continue to spit out antifreeze if you keep adding anti freeze when it is cold as it is normalizing the coolant level for when it is hot. 

120psi on both cylinders, you asked for squish clearance so I'll just tell you about my domes.

Bore size 68.5mm (dome larger then the piston to cover variances)

Step .038" 

squish band width 9.5mm

squish band angle is 10 degrees ( 1 degree divergent angle)

24cc flat plate. 

 

Cap is solid but I have some others I can try. It only spits when it's overheating, I have been unable to add fluid until I get back to camp, so I've tried not getting it spitting hot. I added the excess coolant to top it off because it runs hot, and of my 3 banshees it's the only one having issues and the others are fine topped off. Temp guage is on hose coming out front of the case to the bottom of the radiator, it is tested and works properly. I have not tried adjusting timing but I left it where the guy who did dynotuning had it.