8V71 oil leaks....why?

[JohnEd]

I have pondered the "leaky" two stroke for a few years now.  I have heard a lot of slang explainations:  My engine sweats horse power.....Marks it's territory....etc.

Why do they leak?  I finally looked at that air box and realized that the bottom skirt of the piston is exposed in there.  Does air from the air box enter the crank case and pressurize the innards of the entire engine?  That would explain it to me, but is that the case?  It also followed that as the skirt wore it would bleed more air into the engine crank case so do they leak more with age?


Thank you,

John

[RickB]

I wouls say it is purely to provide us with something to do with our time. Detroit's tend to last so long that if they didn't leak there would be no actual proof that they are there, there is also the conspiracy theory that big oil just needed a more stable revenue stream. Sorry if you are actually asking this question seriously and are really looking for honest and serious answers.

To me it seems as unanswerable as some of the most basic questions of life.

The airbox theory does not explain the #1 issue that I see which is the alternator/generator leaking at it's mounting flange which could probably be blamed on too heavy of a design, too long of a design,(making the lever principle more evident) too much gasket sealant or not enough mounting bolts in the original design. Also, not enough room to fully tighten or retighten the bolts once the engine is in can also be an issue. Add up all those design issues and you have alot of leaky motors. Also, the one way spitter or check valves for the airbox seem to be the other most leaky place for detroit's which can have numerous reasons. The check valves themselves (if you're leaking above the 800-900rpm close point), blower seals, which are as vulnerable to lack of use as they are to high mileage, worn or cracked oil rings, or worn or damaged injectors. That makes 4 different areas where just the spitter tubes are prone to leak.

I think that there must have been a lack of complaints when oil was cheap and the environment wasn't as political an issue as it is now that didn't really light a fire under the designers at Detroit to fix the issues but with the advent of the Series 50 and 60 they obviously were forced to make a less leaky, more efficient new design.

rick

[belfert]

The Series 60 can leak oil too.  I have at least three oil leaks at the present time.  The rear main seal leaks a bit.  I also have a leak from above the water pump somewhere and a leak around or from the oil cooler.  I had a leak at the power steering pump, but a new $3 gasket fixed that.

None of the leaks are serious.  I went on a 4,000 mile trip and the oil was the same level when I got home as when I left even with the leaks.  I am very much considering pulling out my engine to fix these things, but probably not until next spring/summer.

[luvrbus]

JohnEd, a 8v71 doesn't have to leak oil I have been around these engines for while and the leaks can be stopped as most of the leaks come from the top side.   
I have some photos of 8v71's in buses with no leaks I am trying to pm to you      good luck

[JackConrad]

Someone told me that the 71 & 92 engines use O rings to seal many of the oil passages between the block and cylinder head and that these can leak allowing oil to seep from between the clyinder head and block. To repair invloves removing the head, replace the O rings, re-install the heads, re-adjust the injectors, valves, rack, and Jakes (if so eqipped). Or add a little oil as needed LOL  Jack

[RickB]

Brian,

With all due respect if I drove my bus 4000 miles without losing any oil I would probably end up in traction in the hospital from turning cartwheels. Pulling an engine for that wouldn't be something I would ever seriously consider but we all have different expectations don't we?

[belfert]

I don't want the oil leaks to get worse, especially the rear main.  I know Busted Knuckle had an 8V92 where he was losing 3 gallons through the rear main on a trip of maybe 500 miles. 

Pulling the engine is way down on the priority list and everything but the main seal may be fixable in the bus.  My mechanic friend is supposed to come over some day and look at it.

[TomC]

I have seen virtually all kinds of engines oil soaked or leaking-so this isn't a Detroit exclusive problem.  One of the main problems though is that mechanics that do work on the engines have no idea how to seal and keep the engine from leaking. 

My first truck was a '80 KW with a 8V-92TA in it.  I had to tilt the cab many times to show that my engine never leaked.  My 8V-71 in my bus does leak, but I'm slowly getting the leaks out.  This weekend, I'm pulling the sub oil pan to see if it has a crack since it is leaking in one spot, then I can reseal it with a new gasket and sealer.  Good Luck, TomC

[JohnEd]

Tom,

I have seen a lot of 71's that were clean as a whistle.  But they seem to be the exception and not the rule.  The DD2 has a solid rep as a leaker.  SOLID!  They don't seem to put together in any sort of haphazard manner but most are porous.  The only other engine I have heard bad mouthed was the MACK engine(no longer mad, I am told).  DD doesn't have that rep....only their 2 stroke.  I guess they can all leak.  Can you tell me if the crank case is under pressure from blowby in the air box?

There used to be a common problem with gas engines back when smog first brightened our lives.  The crank case breather was replaced with a PCV valve.  When the PCV valve clogged, and they all eventually did if not changed, the crank case got pressurized and the engine leaked oil where they never dreamed.  The common tip off was oil in the aircleaner and burning oil.  It seems possible that this condition could develop in any version of D but the 2 stroke might be especially vulnerable.

Thanks,

John

[TomC]

John- there is a separate breather for the crankcase.  Sometimes it is on the valve covers itself, or like my V drive on the back side (right side of the engine) of the block above the crankcase. It needs to be cleaned just like any other crankcase breather periodically.  The air box is just that-separate from the crankcase.  The only way you can get combustion air into the crankcase is if the piston rings are worn or broken.  Good Luck, TomC

[Airbag]

 I went on a 4,000 mile trip and the oil was the same level when I got home as when I left even with the leaks. 

With my bus that would be EMPTY.    

[HB of CJ]

Yep, now I'm wondering also if that your Detroit didn't seem to use ANY oil in 4000 miles (same oil level) AND you have some small oil leaks, would not that beg a possible explanation that you are replacing any lost oil with diesel fuel?  Have you checked the crankcase lube oil for diesel contamination?  Just wondering.  HB of CJ

[rdbishop]

My last trip to the Eagle rally in La was 800 miles.  I got 8.9 miles per gal and 7 gal of oil per the 800 miles. Pulled the engine out yesterday and put a new rear seal and sleeve today. Hope to get it together and back in the bus tomorrow. Maybe now I'll get a little better oil mileage!!!

Richard

[Dreamscape]

Hey Richard, Now what are you going to do to protect your toad?

~Paul~

[Van]

I hear they are making toad panties LOL