Have some questions about oil starvation and a fix

Discussion in 'Modifications' started by TL_MILLER, Jan 17, 2017.

  1. TL_MILLER

    TL_MILLER Member

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    I need some advice from all the experienced motor builders on the forums.
    Quite a few people have ruined their Grom engines from doing wheelies.
    The oil pick up is in the same location as many of the small Honda engines.
    Right in the front. The question is ... if I were to drill a hole in the oil pickup area and run a line to the rear of the motor, would the oil pump be able to pull oil from the rear of the engine? I would plug the existing hole so it would only pull from the back.

    I know now you guys have 1000x more knowledge than I do about these little motors. The grom engine looks just like the Honda nice motor.
     
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  3. TL_MILLER

    TL_MILLER Member

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  4. kirrbby

    kirrbby Well-Known Member

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    Is there some kind of oil screen or filter to consider??
     
  5. TL_MILLER

    TL_MILLER Member

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    Just a screen like the ct70 [​IMG]

     

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  6. red69

    red69 Well-Known Member

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    Just guessing here, but I from what I see, the oil pick-up relies on a reservoir for its intake. I may be wrong, but I don't think it can suck the oil from any distance as a typical oil pump may do.
     
  7. TL_MILLER

    TL_MILLER Member

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    That's exactly what I was wondering. Someone did some kind of modification with a copper tube. I was wondering if it sucks the oil up from a distance.
     
  8. red69

    red69 Well-Known Member

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    racerx would be a good one to answer your questions.
     
  9. TL_MILLER

    TL_MILLER Member

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    I was hoping he would chime in on this thread. I was either going to split the cases and tap a tube into the oil port hole or run a line on the outside of the motor to the rear. Tap on the bottom of the oil catch and plug the other hole in the motor. I wonder if the oil pump creates a vacuum good enough to pull it through a line.
     
  10. TL_MILLER

    TL_MILLER Member

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  11. motodevo

    motodevo Active Member

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    The only way i can see it working is if you totally seal the original intake to the pump and reroute it to the rear like you have said.As soon as the intake is not totally sumerged in oil, ie an airleak, then there is no vacuum to pull the oil . I wouldn't do it without an uprated/heavyduty pump. How many of these grom guys are running big bore kits without an uprated pump? Unless these wheelies are going for miles on end, i find it hard to believe that oil starvation is from wheelies. You don't hear about it happening with z50s and crf50s, and almost no one installs a big bore on these without upgrading to a hd pump. Yet so many people on the net and even sellers of grom big bore kits say you don't need to upgrade the pump on a grom.
     
    #10 motodevo, Jan 25, 2017
    Last edited: Jan 25, 2017
  12. cjpayne

    cjpayne Well-Known Member

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    Someone needs to seal some plexiglass to the side of the engine. Add the proper amount of oil to the normal oil level, then raise the front to see when the pump should starve( baring in mind how much oil should/might be flowing around when the engine is running). Pretty wild guessing. I don't think the Honda engineers intended the Grom to be a wheelie circus clown anyway.lol
    There was guy around here YEARS ago that rode a wheelie on the highway with an early 70's CB750 and oil starved it to long. He survived, to put it nicely.
     
    #11 cjpayne, Jan 25, 2017
    Last edited: Jan 25, 2017
  13. OLD CT

    OLD CT Well-Known Member

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    I'm not into changing Honda's design. Can't help you there, but if I was going out to be a wheelie king for a day with a CT70 I would run a full quart of oil instead of .7 or .8 :) I don't own a Grom so I can't even tell you how much oil it holds.
     
    #12 OLD CT, Jan 25, 2017
    Last edited: Jan 25, 2017
  14. TL_MILLER

    TL_MILLER Member

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    I would get an uprgraded pump later. Not sure if people are switching the oil pumps after an big bore kit. They should. I've seen a lot of those big bore kits breaking. They don't seem very reliable.

    I also have Ct70's and a Crf50 and wheelie them all day, but you have to be more vertical because of the wieght of the grom.
    I over run oil, about half of a quart. I don't wheelie it very long... don't want to pop the motor. [​IMG]

    I was thinking of maybe buying another case half and having the oil hole welded closed then tapping in an extended oil line.
     

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  15. racerx

    racerx Administrator
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    I think that you already know the answer to this one, don't like it,and hope to hear better news. Can't blame you for that. The bottom line is that this would be complicated beyond practicality.

    Not 100% sure how far the pump can push oil. That said, it is a positive-displacement pump, so that should be a non-issue. The bigger concern would be how well it can draw oil from an extended distance. Unless an extended oil pickup remains filled after engine shutdown, there's going to be lag time...while it refills and that could well be a problem. It's not going to draw air anywhere near as efficiently as oil. The stock setup has the pickup an ~inch away from the pump and oil level, non-running, at oil pump level.

    With a full crankcase, .8qt, oil level is maybe 2" as measured from the crankcase floor. Doesn't take much of a wheelie to expose the pickup to air and for the pump to go into cavitation...a.k.a. "sucking air". You can get away with several seconds of this and the oil flow is restored almost instantaneously once you're back on two wheels. The tranny will provide more splash lube than normal. The top end and rod bearing will be the most affected by lack of oil flow...and begin to heat up beyond normal. Oil isn't just lubrication in these engines, it's coolant, as well. Fortunately, the oil film tales a while to go away and roller/needle/ball bearings don't need a lot of oil.

    With automotive road racers, the solution is a dry sump oil system...or an Accusump system. I cannot imagine either as being practical with one of these little bikes, I'll spare everyone the longwinded tech lecture. Further, changing engine operating angle by 45-degrees +/- is a lot more demanding. You're gonna have to deal with that mean old Mr Gravity and that means locating an oil sump that is always at, or near, the lowest point of the engine...such that the oil pickup is always immersed in oil. I'll end this post with the money question: "how important is stunting to you?".
     
  16. TL_MILLER

    TL_MILLER Member

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    Thanks for the input Racerx,

    I think that's all I needed to here. Your explanations are always the best, very in depth. I guess I will keep the wheelies short for the time being.

    I'm surprised how long some of these motors have been lasting.. with all the long wheelies. I've seen a few people online burning up their motors. These are after many long wheelies. I also know a few guys that just stunt groms in a parking lot. Riding at low RPM's and haven't had an issue. Must be they haven't got hot enough to cause significant damage.

    Stunting is pretty important to me, I stunt almost every Sunday. How much damage would it do from overfilling? I know once it hits the piston it gets air bubbles in the oil
     
  17. racerx

    racerx Administrator
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    The underlying issue is that gravity won't be denied, simple as that. If only the solution were so easy. Continuous oil flow is needed to support this kind of riding, without compromising engine life. What is required is a sump that's always at the lowest point of the crankcase. That'd take two return lines, feeding a deep sump. I reckon that one return line could be plumbed into the oil drain hole, using the existing threads that now hold the drain plug. The other would have to be drilled & tapped, somewhere near the kickstart shaft. They'd need to be sizable lines, to deliver sufficient drainback rates. This might require 1" ID tubing. Keep in mind that the stock setup has close to a square foot of open drainback area and it all gets funneled (more or less) to the tiny sump, where the oil pump pickup is nearly always submerged. That's the second issue.

    An oil feed line would have to be plumbed into the oil pump pickup orifice and well-sealed. That extended pickup would then be plumbed into the bottom of the external sump. There'd be lag time to get oil flowing and I've not a clue how long that would be. As long as the pickup is always submerged, it's unlikely to be a problem.

    That said, the one issue that'll fight you to the death is sheer lack of cubic real estate. The external sump would have to be very deep, and with a small cross-section to maintain oil depth. Can't see where, say, a 6" deep external tank could be safely located, beneath the engine.

    Only way to accurately gauge how much oil is needed to keep the stock oil pickup submerged is to pull the top end, set the engine at the same angle created while stunting, then pouring in oil until it reaches the sump area. Best guess, close to 2 quarts. In any event, the oil level would be above cylinder height, while the bike is being ridden normally, i.e. on two wheels. The windage would be insane. There's a good chance of hydrolocking.

    As for those who "get away" with extended wheelies, they really don't. It takes a while for the oil film to go away and these engines don't need much oil pressure. The top end (valvetrain) can survive for a surprisingly long time on residual oil. The lower end might get by on splash oiling...for a time. However, the cylinder probably won't get uniform splash oiling, the crank assembly will starve and everything from the crank-up will lose cooling. Oil also acts as liquid coolant in these motors. What's actually going on is that they don't run long enough to reach the point of rapid, catastrophic, failure. I'll guarandamntee that wear is accelerated on some parts, shortening service life of the motor. Given enough mileage, they'll be rebuilding sooner than would otherwise be the case. And that is, perhaps, another key piece of this puzzle. Stunt riding doesn't put much mileage on the odometer, so maybe burning-up thousands of miles between rebuilds doesn't matter...to them. Maybe it won't to you, either. You're the only one who can answer that one.
     
  18. TL_MILLER

    TL_MILLER Member

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    I've been thinking a lot about this. Rebuilding every time the cylinder gets starved is not really a good option. So I pulled the trigger.

    Decided to buy a spare clutch cover and try an idea I had. Worst case I wasted a few bucks. The idea was to plug the existing hole for the oil pickup and drill the cover adding an external oil line. Tested it on my fiends grom and it worked. Oil did flow to the top end with the bike sitting at balance point.

    I'm thinking it might be a good idea to make the line a little bigger for more oil.

    auploads.tapatalk_cdn.com_20170321_1e1a3bf82b2510ab45302a371ddca7a8.jpg auploads.tapatalk_cdn.com_20170321_f72ab724d1b7e60d76ca62a22be1f936.jpg auploads.tapatalk_cdn.com_20170321_f72ab724d1b7e60d76ca62a22be1f936.jpg
     
  19. TL_MILLER

    TL_MILLER Member

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    Kinda hard to see the oil. But it's a steady stream.
     
  20. lukelaw1

    lukelaw1 Active Member

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    I love this line:

    "Tested it on my fiends grom and it worked."
     

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