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Note while this is specific to my air-cooled V-twin, I believe other air-cooled motorcycles could experience this problem. I've presented this problem to several people, but no one has a viable solution yet. I'm hoping someone here might enlighten me.

My '95 H-D Sportster 883/1200 (60K miles) is overheating. The oil temp (in the tank) runs as high as 230 deg F. It will heat up to 210 F idling or at 70 MPH, just faster with the latter. It didn't used to get over 200 F.

Bike was recently converted from an 883 to a 1200, but was overheating prior to this. Added an oil cooler with 180 F thermostat, but did not see any significant change. It was running on synthetic oil, but changed to standard (H-D 20W50) for the conversion. No changes.

Valves showed evidence of running lean (grey). Had valve job performed. Rejetted carburetor (has high-flow air cleaner and aftermarket exhaust) with a 45 slow jet (40 original) and a 180 high-speed jet (170 original). The high-speed jet change did slow the heating rate, but did not lower the peak temperature. Went up to 190 high jet with little change.

I'm using the needle from an '89 Sportster (more aggressive "curve") and have installed new gaskets, etc. in the CV carburetor. No Dynajet. I also retarded the ignition about 3 degrees.

My gas mileage dropped from consistent mid-50's to less than 40 MPG. Some of that can be attributed to the conversion, but the mileage dropped to the mid-40's around the same time the bike started getting warmer than normal.

Something just isn't right. The temperature gauge is good. Oil pressure is good. The gas tank/filter may be dirty or clogged, which I'm checking out now. However, I don't believe that would cause the bike to run hot.

Thanks for any suggestions,

     . . . Steve

RE: Overheating

My air cooled dry sump Honda V twin (XLV750) was running very hot for a couple of years,120deg C in the left case where the oil leaves the engine.It was the voltage reg,dumping voltage and overloading the altenator.A new reg and stator rewound and it now runs at 85c.But I don't think the Sportster runs an alt inside the engine?

RE: Overheating

The Sportster altenator runs in the primary/ transmission oil seperate from the engine oil. Have you checked the drive train, wheel bearings, transmission for draging. With the poor mileage you are getting, it seems like something is eating the HP before it gets to the ground. When I infrared the HD,s, if the timing is too advanced the front cylinder runs hotter. When the timing is retarded the rear cylinder will be the hottest.

RE: Overheating

Thanks for the info on the timing, ckenny. I am not confident that my timing is good, since the mark seems to move quite a bit. On cars that I used to time, the mark was usually steady, but this one moves over about 1/4 of the "window". I am trying to acquire a laser temp probe to do a more detailed investigation.

I was thinking that something may be robbing HP also, but haven't found anything unusual. The RPM is very consistent with speed (e.g. 2800 RPM @ 60 MPH in 5th gear). It definitely dropped (about 400 RPM) after the conversion.

Could my ignition module be going bad? Someone mentioned that.

RE: Overheating

Your engine rpm should be directly related to speed via mechanical gears and chains. It should not change with this conversion unless the clutch is slipping. Clutch slip would explain heat and poor mileage, but this seems like a really long shot.

Is there any evidence of high internal friction? piston, crank misalign, etc. That would likely have gotten worse quickly and destroyed something by now.
I would focus on air leaks, lean mixture, exhaust restriction, timing, and the basics of tuning.

I'd like to hear the answers.

RE: Overheating

kcj - RPM is also directly related to HP and Torque, right? I am producing more HP, therefore if the same power is required to maintain a particular speed, the engine does not need to turn as quickly to produce that power.

You're right, clutch slip is a long shot, but possible.

I haven't performed a leakdown or compression test since the conversion. That might point out any problems with leaks, etc. I also have not checked for intake leaks, but I don't have any symptom of such a leak (at least like I had before).

The temperature and mileage were problems before the conversion. I had hoped that the valve job and new pistons/rings and rejetting would resolve them, but they just got worse.

This engine design is very basic. There is probably a simple solution, but I just can't figure it out. You reminded me to look for the simple stuff first. Thanks for the input.

RE: Overheating

I have been trying to find out if the timing rotor is the same for the 883 and 1200 and if the VOES switch is the same setting for the 1200 modification. Does the bike have the stock ignition module in it? Is it the 4 speed chain, or the 5 speed belt drive? Has the cover for the cams been off? There are alot of bushings in that area that can get hot and that is the last place the oil is before it leaves the engine to the filter and tank.

RE: Overheating

As far as I know, the rotor and VOES are identical in the 883 and 1200. About the only drivetrain differences are in the bores, pistons, heads, and crankshaft sprocket.

Stock ignition, belt drive, 5-speed. The cam cover has been off once to replace the sprocket nut, which came loose (that's a common problem with Harleys).

If I suspect bearing/bushing damage, I will pull the cover and check. However, there are no unusual noises coming from that area.

     . . . Steve

RE: Overheating

I wanted to add a couple of notes:

The mileage has ranged from a high of 63 MPG to a low of 36 MPG, depending on the altitude, weather, highway/city, etc. It averaged 55 MPG for 3-4 years, until Spring 2002, when it suddenly dropped to 49 MPG. It's been averaging maybe 46 MPG since then. This change did not correspond to any mechanical work or changes.

The temperature in the oil tank rarely got over 200 deg F for years, even riding in 100+ deg weather. It usually stayed around 190. Then, last summer (2003), while riding thru Kansas, the gauge read 240F when I stopped for gas. Ambient temp was around 103F. Average speed ~ 80 MPH.

Since then, temperature has averaged 200F, then started moving upward a few months ago. I installed an oil cooler, but it did not seem to affect it much. The increase in size just exacerbated the condition, so after idling a long time, or riding at 70 MPH, it hits 230F.

Dinosaur oil (what I'm using for break-in) starts to break down around 250F. Since the temperatures I'm reading are in the oil tank, the oil in the engine must be hotter. I will switch back to synthetic soon, but when I've switched back and forth between regular and synthetic, I have seen little (if any) change in temperature.

RE: Overheating

RPM-Torque-HP  yes and no.
In general terms of physics:
Torque is a twist, without mention of speed. Torque wrench on bolts, etc. It is a force multiplied by the end of the lever arm distance. i.e lbf x feet, or lbf x inches. It would be the measured twist on a dyno output shaft.

Torque times speed is power (work done per unit of time).

Torque ft lbs  times rpm  divided by 5252 for unit conversion is horsepower. Ultimately, this is how all dyno measurements work. Torque and rpm are measured and hp is calculated.

Engine rpm is directly related to wheel rpm because it is fixed gearing ratios, assuming no torque convertor or other slip. i.e. if top gear is 3:1 reduction, then putting a 1000 hp engine on the drive is still a 3:1 reduction, so engine hopup won't change rpm at a given road speed.

What you are thinking of is that for a given output hp, increasing torque would mean the same hp can be achieved at a lower rpm. This is true, and is illustrated by the ability to pull up a hill in 4th gear with big engine, or 2nd gear at higher engine rpm with smaller engine at higher rpm.

However, I think you are confusing hp demanded by the load (which is a constant, depending on grade, wind, etc) vs. hp available from the engine.  

Work backward from the load to determine the hp required: down the freeway at 40 mph maybe only 5 hp is required. Up a steep hill at 40 mph maybe 50 hp is required.  (actually the load determines the tractive effort or force required at the wheel. It's only when speed is entered in, force times speed, that determines hp. For example, if I drop down to 5 mph on that hill, maybe only 5 hp is required because the speed is much less. I am ignoring changes in wind load.)

Anyway, load determines the required force to push it along. Speed times this force determines the power or horsepower. The engine then has to provide at least this power, but no more. If less, the vehicle slows down. If more, the vehicle accelerates. By opening and closing the throttle, we admit more or less fuel/air mixture to the engine, which determines the output of the engine. (Called absolute manifold pressure, I won't go there.) So in this fictitious example, even your 1200 cc engine on flat ground only puts out 5 hp because the throttle is almost closed. The friction to turn things over is very high, a lot of wasted effort in the engine to net out 5 hp at the back, so bad fuel economy.

Now, small engine running with almost wide open throttle is also putting out only 5 hp. It runs just fine, has less friction and pumping losses, and gets better fuel economy. However, when at WOT, it is only capable of say about 6 hp, so it won't maintain speed as the load increases.  With the big engine, running at say 1/8 throttle, we just add more fuel air mix by opening the throttle. This in turn adds more torque AT THE SAME RPM and maintains the same speed up the hill. This is analogous to what you are describing.

Again, the speed is determined by gearing. However, if the little engine pulls the load in some gear at this fictitious 3:1 reduction, the big engine may pull the same load at 2:1 reduction, slower engine speed, higher torque, same hp.

So, bottom line is that the bigger engine may allow you to change the gearing which indeed would slow down the engine, but for the same original gearing, your rpm should not change regardless of what you do to the engine.

Hope I have not left your head spinning in confusion.


RE: Overheating

A hot afternoon across Kansas. I would check the cam bushings. The cams will grow in length and will use the steel support plates on the needle bearing side of the cams as a backer and push the cams tight to the cover bushings blocking the oiling channel on the bushing. I have seen that happen on a few of these engines. The support plate will have a slight blueing and the bronze bushing will show damage. The book says .005 minimum end play however .008-.010 is the happy numbers I use there.

RE: Overheating

ckenny - Now I see I'm gettin' into some WORK. Thanks a lot.

Really, you do make a good point. I haven't been into the right side (cams, timing, belt sprocket, etc.) of the engine. The dealer replaced the sprocket nut (after I identified the problem - the mechanic wanted to rebuild the transmission).

A lot of people that make this conversion also replace the cams in an effort to extract even more power. I hardly ever exceed 3500 RPM, so I couldn't take advantage of the power most aftermarket cams produce above that. However, in replacing the cams, that does give them a chance to check out the bushings/bearings for wear. I may be replacing my cams afterall.

Thanks for the advice.

Now, would this wear increase the oil temperature? I can see how the opposite would occur (higher temps cause more wear). Also, I was running on synthetic oil at the time. I would hope that would minimize the possibility of damage, but perhaps not. Or, maybe the damage occured prior to the use of synthetic oil?

RE: Overheating

The right hand rear cover is the one removed for the the front pully nut. The cam cover does not have to be removed for that job. In my motorcycle shop we have found that when that nut loosens, it can let the spacer behind the pully slip on the main shaft causing the ends of the spacer to wear down. When the nut is torqued it will cause the main shaft to bind. Replacement of the spacer corrects that. If that is binding it will make the engine strain.
The bike will feel hard to push.

I don't think the type of oil is or caused the high oil temp. On a long trip with minimum cam end clearance the outboard surface of the cam can roll the bushing materal into the oil groove on the bushing blocking the oil to that part of the cam and cause the cam to heat up. Those bushings are splash oiled. That is why it is an area to check.

I feel the stock cams are fine.


RE: Overheating

Oh yeah, the rear cover. Forgot about that. Okay, I guess that means the cam cover has NEVER been off.

When my sprocket nut loosened, it made a very loud screeching noise, like the front wheel bearing had seized. I had the bike towed to the nearest dealer. They replaced the bearing, told me it was fixed, but the noise returned within a minute of riding. The mechanics then told me it was a bad tranny, but after discussing the symptoms, it pointed to the nut. They had another Sportster with the same problem come in that day. The following day, the sprocket nut on a Big Twin had come off, causing major damage.

I'm going to check the camshaft(s) end play this weekend. Appreciate the tips.

RE: Overheating

*IF* you don't find the problem, and *IF* you are able to eliminate excessive rolling drag, then I'd start looking at the internal heat-transfer surfaces.  It's possible that your oil cooler/other surfaces are coated with hot/slightly burned oil residue , which is an insulator.

RE: Overheating

OK guys, I've started looking at this problem in regards to your suggestions. Here's what I found so far:

Compression and leakdown were both nearly perfect (180 PSI, 0%).

The fuel filter (in the tank) was partially clogged, probably what was causing the engine to cough and die at times.

The spark plugs were both BLACK and dry - indication of a very rich mixture. That would explain low mileage, but I was running rich in an attempt to keep the engine cool.

The engine starts easily and doesn't make any unusual sounds. I can turn it over fairly easily by hand with the rear wheel while it is in 5th (top) gear. Both wheels seem to turn without unusual drag.

I don't believe I have any intake leaks, since it shows no symptoms and I was very careful about aligning and tightening the intake manifold and carburetor. I will spray some carb cleaner around when I restart the engine to double-check. I don't know how to check for a plugged exhaust, though. The pressure out of each muffler feels the same, and the temperature is around 300F within each (thermocouple about 8" inside exhaust pipe).

Since the entire top end is "fresh" and the bike was overheating prior to installation of the oil cooler, any oil flow disruptions would have to be in the bottom end. I left the oil filter off and ran the engine for a few seconds until clear oil came out. Maybe 5-8 seconds and 1/2 pint. The oil wasn't very dirty.

After looking at what I had to do to get at the cams, I decided I would wait until I exhausted every other possibility. If the bushings/bearings are worn and not getting oil, that would certainly cause the engine to drag. But, wouldn't it also make noise? The engine seems to rev easily.

My timing lite with advance wasn't working, so I had to resort to the old, non-inductive version. I plan on putting the timing back to the factory setting (35 deg BTDC). It should be at 32-33 deg BTDC right now, per the engineer at KB pistons (they suggest retarding the timing 3 deg).

The carburetor mixture also needs to be adjusted.

Keep your ideas comin'. Thanks!

RE: Overheating

Surely if you've put bigger pistons/barrels in and using the same heads then compression will go up significantly.
This will make more heat.
Timing should be retarded - not sure about the 3 degrees.
Flame front travel will have a longer path but occur more quickly - possibly leading to detonation if not spot-on. This will make heat and cause damage.
Lots of people do this conversion so its not unusual - therefore ask a good bike shop to go over it - put it on a dyno and you'll find the answers.

You should go down 1 g'box tooth or up 3 r/wheel teeth to make use of the increased HP or Torque.

RE: Overheating

No, compression ratio is the same: about 9.5:1. That's because I used KB DISHED pistons, which require no head work. KB suggested the 3 degree retard setting.

Most people have said their temperature went up slightly (10-20 degrees F), if at all. I had high temps before the conversion, though.

Good point on the dyno. I guess that's what I'm going to have to do. I don't know how to test for internal drag, like has been suggested. The bike seems to roll easily in Neutral. When it's on a lift, the rear wheel is really hard to move, even when the transmission is in 5th gear. Am I just weak, or is this something to consider?

I am going to take my bike over to a friend that has converted several Sportsters. He can compare my bike with others (and maybe I can do the same) and maybe we can find something. We may start tearing the engine down, too. Not looking forward to that. If we don't find anything, it's dyno time.

Thanks for all the help!

             . . . Steve

RE: Overheating

I have been looking forward to knowing if you have found the problem. A tight wheel bearing could be an area to look at. I know the gentleman who designed the KB pistons. If you would like, I can see if I can get him on line here.

I have given you a star. I had not thought about the effect of over charging has on oil temperature on some engines. I had an engine on a HD with an open in the regulator and the primary drive housing showed it was cooler than a normal system with an infrared scan.


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