Question about 1978 Yamaha RD 250

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Oil pressure loss -

A guy with a 03 dumped the oil(for some unknown reason) while entering the freeway, reving and pulling hard through a few gears. At some point he noticed low oil pressure warning but failed killing the engine. He lets it idle a few hundred meters until next exit. He later filled it up with new oil, engine sounds ok at first but after 10 min it starts going bad with noise and metal parts in the oil. The rest we know.

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  • Anonymous Mar 12, 2014

    I will crank and run fine at first. When it has been running for about 15 min or so, I notice the oil pressure light will come on and off. After that it will start missing and blowing out lots of blue smoke and die. After letting it sit for a few minutes it will crank up and run OK. The blue smoke will go way. What's up with this?? I checked the oil level and it is not low.

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He must have had some other failure. A motor can go for longer than 10 minutes at idle with no recirculating oil. Had an old xr200 that made it about 4 hours with no oil, and we weren't being kind to it.

Posted on Nov 10, 2008

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Loss of opl pressure


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I have a 1993 Heritage Softail, last year I went for a quick ride, stopped at my buddys, 20 min later we left, we got 5 miles down the road, all the oil pumped out the Air filter. I let it cool down filled...


I've run into this problem before. Unfortunately, the owner wrecked the bike before we solved the problem. Here's what I found so confusing. If the top end is filling up with oil and not draining down the return holes in the heads and cylinders, it should drain down through the pushrod tubes. Each tappet has a drain hole in the tappet block to allow oil to drain down and not build up in the tubes. But, for some reason, it seems that the oil simply will not drain back. It acts like there is too much pressure building up in the crankcase. It wouldn't do it on short rides, just on rides of about 20 miles or more.

So, with this in mind, my next step was to pull the nosecone and check the breather gear. As you know, the Evolution engines have plastic breather gears in them and I've seen lots of them break a tooth and quit turning. Usually, the broken tooth gets hung in the return gears of the oil pump and shears the drive key. This requires that this be fixed before the engine can be run and the pressure build up noticed. But, if the broke plastic gear tooth does not lock up the oil pump, the breather gear not turning could be the reason for the pressure buildup in the engine. Now, you cannot simply take the bolts out of the nosecone and pull it off. You must deal with the ignition system first then the cam and tappets. The book says that you must pull the pushrods out and take the pressure off the cam or you will not be able to get the nosecone back on. If the breather gear is broken, you'll have to retime the new one and the cam unless you replace it with one of the new S&S Reed Valve type breather gears that do not turn.

Now, this is just a guess on my part. Since I cannot see or touch your engine, this is the only idea that I know of provided the oil pump is pumping the oil back into the oil tank. It's your engine blowing oil out for no apparent reason. I had the problem on a '91 FXR which is not a head breather. It just leaked oil from everywhere. pushrod tubes, rocker box gaskets, base gaskets, everywhere. I'd like to know what you find.

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