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overheating?!?!?

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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I'd like to start by saying that this forum has saved me tons of money and thanks to everyone who helps me out on this! My bike is a 1978 GS 750.It has K&N pod filters,vance&hines 4-1 exhaust,and a henry abe 852cc bore kit.

After going through all of the hastle getting new cylinder jugs (the old ones were way out of spec,about 2mm)I finally have the bore kit installed. My problem is that the bike is now overheating. after about ten minutes of riding the bike starts to blow white smoke out of the breather on top of the engine. When this happens the bike really doesnt seem to loose much power but I never run it long after this starts so I really don't know. I thought that the bike may not be getting proper lubrication so i pulled off the oil pan thinking that the filter screen may be the problem. The oil pan had about 2 good size oil rings worth of material in it. I cleaned that out and cleaned the filter screen. After that and an oil change with a new filter the bike is running much better and stronger but it still heats up after about 10-15 minutes. It's not smoking as bad(instead of thick white blinding smoke it is about the consistancy of something like cigarette smoke). Is there something really wrong here or is it something as simple as the cylinder wall is to thin and is heating up too much. If it is just that the bike can't get rid of the heat fast enough could this be fixed by running something like a lockheed oil cooler? I heard someone say that a oil cooler could be hooked up through the oil gallery plug. How do you do this. If there is already a post like this i apologise and could someone send me in the right direction.

Thanks for your help everyone!

HST564 :cry:
 
I meant lockhart not lockheed oil cooler and i also have a dyna electronic ignition on the bike, I don't think that it really makes any difference with this problem but I want to cover my bases.

HST564
 
It may just be tight from the rebuild. What compression is it running? Turn the mixture screw out 1/2 turn, make sure it is not running lean--check the plugs! (under side of carb) Take it out on the Hyway and run it easy and vary your speed/rpm for 20-30 miles for breakin. Oil cooler would help too, it requires a special adapter that replaces you oil light sending unit under the carbs. With fresh gaskets I would consider going to Synthetic oil. After you have 50 miles retorque the head bolts
 
heater

heater

I dont know how much timing varaition this model will allow but is your timing correct? does it have a mecanical advancer ? and is it working freely?
 
Thanks for all of the quick input! I pulled out the spark plugs and they are all black. The plugs are the correct NGK 8ES plugs so I's assuming that the bike is just running really rich. Would running rich cause this much of a problem? I tried to turn the screws out a 1/2 turn but that did not seem to remedy the overheating issue. Also I checked the timing and it is dead on. Any other ideas?

HST564
 
are you sure it is over heating?
have you done the water sizzle test?
running rich will actually help cool it, the extra fuel cools the incoming air more and also lowers the combustion temps.
a oil cooler is a good addition to a big bore engine. also painting the engine black and running synthetic will help greatly. it has been found that Volkswagen (air cooled real VW's) engines with the valve covers painted black, run 30*F cooler!!!!

never chrome your cam cover, it will hold in heat and cause engine to over heat!
 
Tell us what the spark looks like. Blue? Orange? Use a new plug correctly gapped and check at all four caps. Also, what changes did you do to the jetting? Are you using the stock carbs?
 
What is the water sizzle test? The bike is running the stock carbs but i dont know if there are any jetting changes because i didnt put the filters or the exhaust on the bike. The spark is fat and blue like is is supposed to be. Just curious but why would black help the engine cool faster? Should i paint the whole engine or would just painting the jugs or the head be sufficient?

Thanks!,

HST564
 
Having white smoke coming out of the breather doesn't necessarily mean your motor is over-heating. I think it's possible your valves need adjusting and/or you have oil getting past a guide seal. As soon as the motor is hot enough, the oil will burn white. Another possibility is fuel contaminated the old oil and got past the rings. The rings may be sealing better with the fresh oil? It could also be a combination of these things?
Your petcock or float needle valve(s) may be allowing fuel to enter the crankcase.
As for the black plug readings, you say the timing and spark are good, so I have to think the carbs need adjusting and/or re-jetting. There are several things that can cause your carbs to be rich.
If the carbs were mine, here's what I'd do.
Clean the carbs and used compressed air to blow things out. Check/replace any bad o-rings, including the manifold o-rings. Check the choke circuit/plungers for operation. Check/adjust the floats and check the float needle valves condition. Check the jetting set up. Are your pilot jets #15? What size main jets? Can you see a # on the jet-needle and what position is the e-clip in (from the top)?
IF YOU BELIEVE the jetting is OK, then you may just need to fine tune the carbs. A vacuum tool carb synch on these VM carbs is mandatory. You can also do some fine tuning with the pilot fuel screws that will effect performance up to 1/5 throttle position. The side air screws are to be adjusted for the highest rpm's possible. You then re-set the idle to about 1,100 rpm's with the idle adjuster knob. If your problem is beyond 1/5 throttle, you need to make needle and main circuit changes.
It's hard to narrow down the problem without knowing exactly how the carbs are set up and their condition.
 
the sizzle test is where you drop drop of water on fins of intake side of head, the water should just sizzle off or steam off, if it jumps around and off the engine is hot.
black conducts heat better.
painting the sump cover and cam cover will help dissipate heat, it is reason good radiators are black and one of the reasons 83 and later GS E engines are black.
depending on your location, a oil cooler is a good addition.
 
I'm going to try the "water test" this afternoon. When I had the engine tore down so that the cylinders could be bored out I noticed that the valves looked like they may need to be replaced. They looked pretty burnt up.I didnt have the valves done due to money isseus (In hindsight this seems pretty stupid). Could this be the problem? If the valves need to be replaced would this allow oil through into the cylinders? If so why would that cause the smoke to come out the breather. I thought that the breather is for the crank case. Also would the carbs being off make the engine heat up this much? It seems to run fine beside the smoking, but I'm going to take off the carbs tonight and see what i can find out. How much would it cost, on average, to have the top end rebuilt with new valves,guides,pretty much the whole works? I really appreciate all of you helping me out with this.

THANKS,
HST564@Yahoo.com
 
How could I tell if the issue is from something like a valve guide seal? I talked to a couple different mechanics and I was told that the issue was probably just a guide that is too worn down. Is there a test I can do or do I just have to replace all of the valve guides? If I do have to replace all of the valve guides how much should something like that cost? I was also told that the rings may be misaligned, but the mechanic that i had rebuild the engine assures me that they are in correctly. Does anyone know if there are still people making/selling the oilcooler adaptor plates for gs750's? I saw that there were a couple people who may machine them for the right price.

Thanks,
HST564
 
I don't have enough experience to advise you on testing/repairing the valve train, or determining exactly which part may be failing.
I would do a compression test and go from there. Try to get a recommended mechanic. If you're keeping the bike and have the money, then I'd replace everything that's necessary.
If that means all the valves and guides, etc, then that's what I'd do. It may just be hardened seals.
See what the compression test shows first. Respected shops around here such as Vance & Hines, charge about $60/hr labor.
 
Does anyone think that it would be worth while to just put in all new valve stem seals? I have all of the seals i just need to put them in, but i dont want to go to all that effort if that is not the problem.

HST564@yahoo.com
 
Usually valve seals will smoke at idle, and on decelleration, but not on acceleration, or at least not much. You may be able to tell by taking off your exhaust and looking in the ports. I have one seal that leaks, and you can see the valve is colored different then the rest.
 
I took the bike out tonight to see if it was overheating or just smoking. I brought the bike back in after a twenty minute ride and tried the "water test". The water didnt even really sizzle. The bike doesnt seem to be running hot at all. It is still smoking and i noticed that around the far left (#1) cylinder oil was leaking from the end cover on the exhaust cam side. I'm assuming that this is nothing more than the end plugs getting old and brittle and not sealing up very well. I'm going to try to run some hotter plugs on the bike and see if that helps at all. any more ideas about the valve train?

Thanks for the help!

HST564
 
Black radiates heat better than bare aluminum, but black paint does not conduct heat better. A heavy layer of black paint will be like insulation, the heat won't conduct through the paint very well.

Heatsinks are anodized black aluminum, this gives you the ideal emissivity of a black-body (translation, it radiates heat) without the insulating effect of paint.

In other words, painting the engine black can actually do more harm than good. If painted, the paint layer should be as thin as possible!!
 
Hotter plugs are just an attempt to compensate for the real problem. Compensating just creates more problems.
If you want to try to stop/minimize the oil burning, try an oil additive that helps the seals, etc. Sometimes they work and you may get several thousand miles before the problem returns.
I never thought your motor was over-heating. It's just burning some oil.
You never answered how you re-jetted for your mods though.
 
Hotter plugs are just an attempt to compensate for the real problem. Compensating just creates more problems.
If you want to try to stop/minimize the oil burning, try an oil additive that helps the seals, etc. Sometimes they work and you may get several thousand miles before the problem returns.
I never thought your motor was over-heating. It's just burning some oil.
You never answered how you re-jetted for your mods though.
When you say the plugs are black, are they a shiny/sticky black, or a dry/sooty black?
 
I havent had a chance to take a look at the carbs yet to find out their settings. What kind of additives work well for stopping this kind of leakage? Would just adding oil additives work or is that just going to mask the issue and not resolve it? Will just putting in additives and not really correcting the problem cause any real harm? I really appreciate all the input from everyone! I cant imagine how long and how much money it would have cost me to get even this far!

THANKS,

HST564@yahoo.com
 
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