Overheating GS850g

[gwatson27]

I'm well and truely stuck. My 1981 gs850g seems to run at a temperature >154C in 9C ambient weather - There are no air leaks - it runs on Shell E5 - the spark gaps and timing is spot on - I've tried uping the main jet size in the carbs from 115 (stock) to 130 which made the throttle lag but had no meaninful effect on temperature - the carbs are balanced it idles spot on 1000rpm and with the stock jets it rides perfectly ........ but the engine is so hot the paint (rated to 288C) is discolouring and it turns the oil chocolate brown in 50 miles - I am I'm totally out of ideas.

I've measured the temperature with little temperature stickers which I place on top of the top cooling fin either side of the cylinder head exhaust side - idling from cold the engine will crack 110C on the LHS and 100C on the RHS - In less that 2 miles in a 60mph limit going up and down the gears it hit 154C - the exhaust pipes have turned yellowy blue.

The engine was rebuilt by an engine shop with fresh piston rings, re-honed cylinders, reset valve tension and shims and all the internal components checked for wear as per the workshop manual. - This was the 2nd rebuild as I'd previously rebuilt it myself and discovered 100 miles in that some grit had made it into an oil channel while I was blasting the casing, So I gave it to a proffessional to strip, clean and inspect. It was running hot after the first rebuild too as the paint and exhaust discoloration started then.

Has anyone experienced this before? I'm down to suspecting the paint is too thick and creating a thermal barrier between the engine and the air which seems daft frankly

Does anyone know how externally hot these air cooled engines are supposed to get? I'd have though 120C would be the absolute max

[Wingsconsin]

http://www.youtube.com/watch?v=UeCLRoioe8g

This might help some ??

[Nessism]

I'm well and truely stuck. My 1981 gs850g seems to run at a temperature >154C in 9C ambient weather - There are no air leaks - it runs on Shell E5 - the spark gaps and timing is spot on - I've tried uping the main jet size in the carbs from 115 (stock) to 130 which made the throttle lag but had no meaninful effect on temperature - the carbs are balanced it idles spot on 1000rpm and with the stock jets it rides perfectly ........ but the engine is so hot the paint (rated to 288C) is discolouring and it turns the oil chocolate brown in 50 miles - I am I'm totally out of ideas.

I've measured the temperature with little temperature stickers which I place on top of the top cooling fin either side of the cylinder head exhaust side - idling from cold the engine will crack 110C on the LHS and 100C on the RHS - In less that 2 miles in a 60mph limit going up and down the gears it hit 154C - the exhaust pipes have turned yellowy blue.

The engine was rebuilt by an engine shop with fresh piston rings, re-honed cylinders, reset valve tension and shims and all the internal components checked for wear as per the workshop manual. - This was the 2nd rebuild as I'd previously rebuilt it myself and discovered 100 miles in that some grit had made it into an oil channel while I was blasting the casing, So I gave it to a proffessional to strip, clean and inspect. It was running hot after the first rebuild too as the paint and exhaust discoloration started then.

Has anyone experienced this before? I'm down to suspecting the paint is too thick and creating a thermal barrier between the engine and the air which seems daft frankly

Does anyone know how externally hot these air cooled engines are supposed to get? I'd have though 120C would be the absolute max

Measure oil temperature after a ride. Never let your bike sit and idle for more than a few minutes, since there is no air flowing over the engine.

Oil temps up into the mid to high 200F range are normal for GS bikes, and there are rarely problems caused by it.

[oldGSfan]

How many miles since the rebuild? It'll run hotter until it breaks in. I was getting 325°F (162 C) at the cast iron cylinder after a rebuild on my Norton, and it dropped to around 275°F (135 C) after 1K miles, measured right after a good long ride. That's with painted barrel. I asked about it on a forum and the consensus was "it's fine." The oil in the tank is a bit over half the temperature of the engine. I don't think your temps are a worry for the robust Suzuki but it's good to question and find out what's right.

[Rob S.]

Do you have an external oil cooler on it? My '82 11E ran very hot in the summer until I installed a Suzuki cooler from an 1150. The amount of temperature difference was amazing.