Mystery built engine question for all you engine gurus

Well about a year ago I aquired an engine on ebay for my yz426f which was supposidly built by a reputable builder of shifter carts. Well when I put it in my bike I noticed it had a Dr D oil block off plate installed in the spot that returns oil to the tank in the frame. I never though much of it untill recently when I got another yz426(this one's plated :banghead:) and noticed how the oil actually registered on the dip stick. I used to just put about 1.7 quarts of oil in it and call it good but now I've been trying to make it register on the tank stick of the built engine bike (like 2.5l). Well tonight I actually pulled the head to check valve clearences, wear and what not and decided to loosen and check oil flow at each point and relized that it wasn't being pumped back into the tank in the frame (head oil pres. was good). Mystery solved on the dipstick i guess but now I have a new question. I'm guessing that the oil block off plate was there because they disabled the oil passage or something and just changed the oil every run (please correct me if you have a better theory); but how much oil should I use now if I'm just filling the engine on a yz426 not the tank? Could the capacity have been increased internaly or anything? I'm afraid of not running enough oil but how much is too much if I'm adding it to the tank but it never comes back to check on the dip stick? Should I just bypass the tank all together, or still use it for filling, breather, etc.?

I'm not too familar w/ the internals of these engines but hope to get through the rest of the season before I pull the head/engine (rode it through last season w/o issue). I just don't wanna hurt anything as the heads, etc are expensive. The valve clearences were good and all so I don't think I've hurt it so far. What do you guys think about the whole thing?

Does not having oil go through the tank in the frame present a big problem? I don't mind more frequent oil changes or anything. Is it common to block oil off like that?

Thanks for any insight you can provide guys,


Your mystery engine has a DRD wet sump kit. This conversion turns the normally dry sump engine into a wet sump, and reduces the oil capacity. Among the reasons given for doing this is weight reduction and lowering the CG by moving all of the oil into the engine. The downside is that the oil needs to be changed just about every hour.

To restore the engine to a dry sump, you will need to remove the after market plate and reinstall the return pump rotors. If you ask the guys at Dubach Racing Development, I'm sure they will give you the full details on what needs to be done to reverse the mod.

That makes alot of sence, thanks for shedding some light on that.

What are the positives and negitives's to running this kit? The oil stays pretty clean and I generally change it every 5hrs w/ synthetic anyways so I don't mind that part at all. Is it any less reliable or cause more wear on the engine? What amount of oil should I run. Would the side engine plug (the one you need a big flathead to unscrew) be a good way to check the level? Untill it stops spilling out the side kind of thing?

Are those kits noisy? I do have this weird noise that sounds like it's comming from the head, but it's probably the oil pump. It scared me at first, but I've put atleast 50hrs on that thing in pretty hot weather since new and never had problems. Like i said before, I know it's getting oil to the head and the cams, etc look fine. Any experience w/ these things and thier noise?

Thanks again for the quick help,

TT Rules!!

Like Grey mentioned the oil needs to be changed much more quicker than a stock motor, DRD recommends oil changes every hour for these. Stock motor is every 3-6hrs

The wet sump conversions are a serious, race only mod, and even among pro teams, most didn't use it on the steel 450's where it did the most good.

Oil capacity of the stock 426 was 1.6L with the wet sump kit, it's less than half that. With the kit, the neutral switch (near the shift shaft) is typically replaced by a sight glass, which is used to check the level. That would be nowhere near the big timing plug you mentioned. You could never run the oil that far up the crank, anyway. No external lines are used with the kit, and if you connect them, you'll cause problems.

With the kit, you reduce the oil capacity to half, the oil gets dirty 2-3 times faster, shears down 2-4 times faster, and runs hotter. On top of that, you introduce all of the wet sump issues, like oil sloshing away from the pick up screen, that dry sumps eliminate. I would never run such a setup for any reason.

Ya, I think i'm over it. I was more of a car guy before I got into riding and the dry sump was what you wanted for extreme machines. The wet sump gets oil slosh and what not like you guys mentioned. I assume the kits are reversible right? I tried to go out riding today and think I threw the rod/crank bearing as It locked up around the corner from my house (too much oil didn't help I'm sure). When I kicked it over a few times softly, it just didn't have that nice precision machine smooth feel anymore. I can still kick it around so it's not too serious but it will still need a tear down and build up so I might as well go back to stock to the oiling system.

What did these systems go for back in the day? I can't seem to find anything about them online. Maybe I can get something for it on ebay.

You were dead on w/ the sight glass thing too. It just gets too dirty to see after a good ride.

Thanks again for all your help. It really helped solved some good questions I should have asked a long time ago, but hey that how you learn.


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