My 1990 FLHTP got primary chain case oil leakage problem but I am not sure what caused it. The symptom is, most of the primary chain case oil is “sucked” into engine oil tank. I guess it is going from the stator axel into the crank case then engine tank since it should be the only place that primary case connecting with engine. I am not sure my guess is right or not. I have inquired the mechanism but he replied that he never met this kind problem before so he also not sure what is the problem. Did anyone here meet this problem before? If I added enough oil into both primary chain case and engine oil tank, the oil in primary case will be sucked into engine oil tank soon and caused it overflowed finally. It is very strange that only primary oil go to engine but not engine oil go to primary case. It seems that the engine room pressure is lower than primary case cause the oil going one-way only. In order to avoid the engine oil tank overflowed, I am thinking not to add enough primary oil. What it will cause if I do not add enough oil into primary case? Thanks if anyone can help

 

Does your engine use engine oil to lubricate the primary? If so you may have a blocked return line. If not, You probably have a bad mainshaft seal and the primary oil is just migrating in there when the bike is hot and just turned off. But the bike resting on the jiffy should cause oilin the primary to flow away from the seal and pool at the outer case side.The primary is a splash oil system so there is really no oil pressure. The engine is pressurized but vented and no pressure when turned off after the oil has returned to the tank. It is probably a very small leak and just enough when theengine runs. This would be evident if it takes a long time for the primary oil to migrate to the engine. If it migrates quickly...then you have some negative pressure issue in the engine that is sucking the oil past that seal or the seal is just bad enough that the negative pressure from the oil returning to the tank is enough to suck oil past the seal when the engine is hot & the oil is hot and will flow past the seal.

In either case my guess would be that seal. Could be a venting issue with the engine but the seal should still hold the oil back in the primary. There could be a void in the crankcase gasket or a crack in the engine or inner primary case as well so that should be checked as well. Also some of the engines use "sealing" fasteners to bolt the inner cases together....check those as well.

Oh if your primary runs out of oil it will burn up your chain, clutch and pretty much everything else in there.

 

Dear KBFXDLI
thanks for your information, it very helpful.
My bike using 20W-50 for engine and 75W-90 for primary chain case, so, it should be independent lubcant system. When I found the oil leak problem. It is very serious already. The primary fluid flow to oil tank very quickly. When I added one bottle of the fluid into primary case then turn on the engine. Almost 2/3of the oilwill flow to engine oil tank after the bike run few miles. That why I am using "sucked" to describe the leakage. Since the oil only flow to oil tank and no sign of leakage from the outside body of the engine, so I think your guess maybe right, it may caused by the bad seal. I will ask the mechanicto take apart the primary chain case and check it. I wish it is only seal rpoblem, not crack of the engine body, otherwise I got big trouble. thanks

 

Tell your mechanic to replace the front motor sprocket seal AND the bushing making sure to put the open end of the seal facing the primary and NOT the engine. While he is in there he will want topush up and down on the front shaft and see if any oil squeezes out between the case and the bearing. If it does than the case is out of tolerance and will need to be replaced as the bearing is no longer fitting tightly into the casting itself. The vacuum created by the upstroke of the front piston is actually sucking the oil in and BOTH the bearing and the seal & bushing need to be at correct tolerance and oil tight. He should also check the shaft to see if the seal has scored it. If so, it will need to be replaced as well. You may want to price a new bearing as well while you are in there. It should be a timken bearing and not horribly expensive. This job is all labor as there is not a big cost in parts unless the case id bad.

Good luck...hope this helps. KB

Oh yeah....use 75w90 gear oil in the transmission and Harley Primary lubricant in the primary. 75w90 is way too thick for the primary

 

Dear KB,
thanks for your advice. I had my bike fixed yesterday. Michanic took apart the primary case and inspected the bushing & seal. The bushing has obvious one cycle of worn out mark on it. As the seal, mechanic claimed it maybe aged due to the engine too hot. I asked him to replace the bushing and seal. It took about 2 hours and labor & parts charged $100.After repaired, I run the bike about 100 miles then re-check the oil tank. There is no extra oil appeared. It seems no leak oil from primary now.But I will keep watching it for a while.
May I ask another question? Is the crank case preasure negative correct or not? In your reply, said that my bike having "negative preasure issue...", sound like the crank-case negative-preasure is not correct.
Besides, I have installed an oil preasure & temperature sensors at the oil-filter by myself. The oil temperature shown between 90~100 C when my bike in highway speed. It will go up to 130~140 C when trafic jam. Is it right for bike?
As the oil preasure sensor, it always shown negative ever since I installed it. I am wondering it is out of order or the oil preasure is negative at the oil filter? thanks

 

There should only be positive pressure in the oil system. The negative pressure that was sucking oil past that seal was most likely the vacuum created by the upstroke of the front piston. That is what I meant by negative pressure.

Oil temp 90-100C is about 190-210F which is normal operating temp. However 130-140 is pretty hot and almost hitting 290F which will cook dino oil. Since you have an older bike if you are not running synthetic oil you might want to consider changing oil at 80% of the recommended mileage change interval as it will shaer out of grade faster with that heat. I would not switch to synthetic oil if you are not running it now. You could also consider installing an oil cooler if you don't have one. But simply shortening the oil change interval should suit your needs. You should be runing a motorcycle rated 20w50 like HD360 or a 15w40 HDEO like Shell Rotella. My first choice would be the HD360 20w50.

Oil pressure...if your gauge is reading negative it is probably out of order as with no oil presure your engine would have melted a long time ago.Your oil pressure may seem to drop to zero when hot at idle on your gauge but it should go up to 30psi +- under acceleration and when cold

Good luck...hope this helps. KB

 

thanks for your advice. Since the engine oil has been mixed with chain case oil during the leaking. So I need to replace the entire engine oil and oil filter immediately. I will use this chance to inspect the oil preasure sensor and replace it if necessary.