'79 GS1000S - 1085 Wiseco Kit - overheats at low speeds

[Fjbj40]

Less thickness in the cylinder wall will cause less heat to be transferred to the cooling fins and more heat to the oil. The thicker walls absorb more heat and transfer it to the cooling fins, if the cylinder walls are thin the next cooling agent, oil, absorbs the heat. Without an oil cooler the 1000 8 valve engine gets hot, as the engineers designed it to cool with air only.

[Nessism]

Less thickness in the cylinder wall will cause less heat to be transferred to the cooling fins and more heat to the oil.

I'm not convinced this is true. Steel holds heat and doesn't transfer it very effectively. Removing the liner all together is the best way to transfer heat away. That's why so many modern engines have go to coated aluminum cylinders.

[Fjbj40]

And they are liquid cooled.

[John Park]

An oil cooler was exactly what the doctor ordered! On a slow speed ride through traffic today the oil temperature barely reached 100C (212F). On the same ride a few days ago, with no oil cooler, I saw it reach 150C+ (300F+) and it was still climbing before I stopped.

Based on my experience, if you are putting a big bore kit in your 1000cc 8V you should also install an oil cooler - and it does not have to be a big one as you can see from the photo below. I sourced mine from an unknown model of Kawasaki.

Thanks everyone for your contributions to this thread.

This is nice to know; I live in an area where it's often 35C - 39C today - and even my 400 gets hot oil; I can tell because the idle goes higher as there's lots of bearing drag in a twin what with the counterbalancer.

I think a lot of the problem is that the exhaust pipes heat the air that flows to the engine, which isn't a big deal if the air is being replaced fast but at low speeds it just pools around the block, which screws up the oil cooling. Once you're moving fast enough to get the hot air from the pipes going back instead of up, the oil pan can go back to cooling. Putting a cooler up in virgin air is perhaps a bigger change than it would look like. Plus, even a small cooler can be effective if the oil spends enough time there, which would be the case at lower rpm.

Twins are a little better off as they have the pipes splayed outwards, half as much exhaust pipe surface area and no inside cylinders, but it's still problematic. I've just learn to avoid the situation as much as possible, and to give the motor some time to cool down afterwards before I get on it hard.

[Nessism]

And they are liquid cooled.

The point is that having a heavy steel jacket around the piston does NOT increase heat transfer to the outside cooling medium.

[Fjbj40]

Weight has nothing to do with it. It is heat capacity. Less meat = less heat absorbed, more heat stays in engine, engine oil temp increases.

How thick are the modern aluminum cylinder walls? Never worked on one, but I would bet they are thicker than a steel cylinder wall. Are they used in air cooled engines?

[Nessism]

Weight has nothing to do with it. It is heat capacity. Less meat = less heat absorbed, more heat stays in engine, engine oil temp increases.

How thick are the modern aluminum cylinder walls? Never worked on one, but I would bet they are thicker than a steel cylinder wall. Are they used in air cooled engines?

I believe this info about thick liners leading to reduced engine temps is incorrect. Best situation is to move as much heat as possible out to the cool cylinder fins. A thick liner will absorb more heat than the thin liner, thus more heat is retained in the engine, not transported outside.

The downside of thin liners is they will distort more than a thick liner. This is not good because you can lose your piston ring seal. Ideal situation is a balance of these factors.

[Fjbj40]

Yes on thin liners causing being distorted and loosing compression. One of the reasons I am keeping my eyes open for a set of 1100 8 valve cylinders, along with the hopes that oil/engine temps will decrease. The oil cooler takes care of it for now.

I am basing my experience on the thin walls causing overheating on air cooled aircraft engines. Both of the major engine manufacturers, Continental and Lycoming, advise strongly against it for loss of cooling effectiveness, they also do not provide O/S pistons based on this. Along with my first hand experiences with the 1000 engine I believe this to be true.

That being said it is not the ONLY reason for the increased temperatures, the increase in compression ratio is also a contributing factor.

I think the thicker cylinder walls hold the heat and the cooling fins dissipate it. If the cylinder walls are thinner then the heat gets transferred to the oil. If they are the same thickness as originally designed it sorta stores the heat till the Cooling fins dissipate it. Fark knows

[gs11ezrydr]

You mentioned a ping at times have you properly set the ignition timing and then check it at full advance? Is your advancer working properly also? There is a ratio that for every degree of timing it raises the temperature of the machine in effect. An old nitro burning friend told me this years ago. I think in nitro 1degree of timing raised the engine temp approx 9-12 degrees.. Which crosses over into gasoline burning engines also but I don't believe at the same ratio. But still raises it. Don't know can't find my chart. Also good fuel will only help things. Besides an oil cooler also.

[IanR]

You mentioned a ping at times have you properly set the ignition timing and then check it at full advance? Is your advancer working properly also? There is a ratio that for every degree of timing it raises the temperature of the machine in effect. An old nitro burning friend told me this years ago. I think in nitro 1degree of timing raised the engine temp approx 9-12 degrees.. Which crosses over into gasoline burning engines also but I don't believe at the same ratio. But still raises it. Don't know can't find my chart. Also good fuel will only help things. Besides an oil cooler also.

Interestingly and relevant to your post, shortly after I rebuilt the engine with the BB kit installed and when the overheating issue became apparent, I found that one of the 2 springs that are part of the ignition advance unit had broken - meaning that it would go fully advance far too early. I replaced both springs and checked the timing was correct, but all I saw was that the engine took a little longer (hard to quantify) to overheat. By the way, at no stage, even with one broken ignition advance spring, did I notice any pinging - I usually run 95 actane fuel.

[IanR]

This is nice to know; I live in an area where it's often 35C - 39C today - and even my 400 gets hot oil; I can tell because the idle goes higher as there's lots of bearing drag in a twin what with the counterbalancer.

I think a lot of the problem is that the exhaust pipes heat the air that flows to the engine, which isn't a big deal if the air is being replaced fast but at low speeds it just pools around the block, which screws up the oil cooling. Once you're moving fast enough to get the hot air from the pipes going back instead of up, the oil pan can go back to cooling. Putting a cooler up in virgin air is perhaps a bigger change than it would look like. Plus, even a small cooler can be effective if the oil spends enough time there, which would be the case at lower rpm.

Twins are a little better off as they have the pipes splayed outwards, half as much exhaust pipe surface area and no inside cylinders, but it's still problematic. I've just learn to avoid the situation as much as possible, and to give the motor some time to cool down afterwards before I get on it hard.

One of the reasons I really needed to sort out this issue is that if my bike was overheating in Sydney during winter where typical daytime temperatures reach 15C-20C (59F-68F) I, like you, was going to be in big trouble in summer when it can and does get much hotter.

In relation to the exhaust pipes contributing to the issue: I found that the area of the engine that got REALLY hot was the head - a drop of water on one of the head fins would ball up and bounce around, not just spread out and boil off. This is evidence, I think, that the extra compression of the BB kit placed a greater heat load on the head contributing to the need for better heat removal via the oil and the new oil cooler.