New Blower Needed?

[tmathis]

The 8v-71 in my Eagle was using a bit too much oil. I pulled the intake and screen to look at the blower. Both endplates were covered in a black oily residue, parts of both lobes had the same, especially toward the back of the engine (front of the bus), shouldn't they be clean? But most worrisome was the raised portion of both lobes that makes contact with the other lobe had scratches perpendicular to the length of the lobe. The scratches were deep enough to catch a fingernail. I am thinking this thing is just worn out. Never been down this road before so I appreciate input from those who have. I found a place in Dallas who will sell me a rebuilt unit pretty reasonable. If you have any opinions on a source for a rebuilt let me know also.
PS I was able to rotate the lobes by hand about 1/8 - 1/4 turn, is that normal?

[TomC]

Time to rebuild the blower.  And no it is NOT supposed to have that much play.  I would suggest you not drive it again till you rebuild the blower.  If the blower goes, the engine doesn't go.  Good Luck, TomC

[JohnEd]

I think the gear that drives the blower gets worn and will eventually shear.  Also , there is a entire gear train that drives the cams.  That gear train can disintegrate as well.  When the engines get an "in-frame" that stuff doesn't get serviced but it should get checked.  The problem here is that if you loose one of these gear trains you grenade  the engine.  There is also some sort of "adjustment" for the gear mesh and leaving that unadjusted wears things out pretty quickly.  You need expert 2 cycle smart help from a honest shop.   Cheap might also help but smart is the real critical element of their attributes.   Do you have a gear driven alternator?

John

[BusCrazyinFL]

http://www.dieselpro.com/  I just had my rebuilt by them good price 490.00

[tmathis]

well, the alternator is belt driven for what it's worth. I think I'll order the rebuilt unit then get into the slop in the gears once i have the old blower off of the engine. We'll see how big of a can-o-worms this turns into.

[JohnEd]

Good for you Tony.

I looked at a bus with a blown engine down in Roseburg, Orygun.  I was told that it shearede the cam drive gear and that there were probably a "couple" bent valve stems.  What a CARD!!!!!!  It was an 8V71 anchor.  I trust that will not be your fate and I feel good about that.

I hope you post about what you find, the adj that was required and how it all went.....and cost.  That was a superb price for that rebuilt I am sure.  As always though, find out what Clifford could have gotten it for and that will define the POSSIBILITY.

Good luck with your adventure,

John

[Geoff]

Other than the "1/8-1/4 turn" of the rotors the visual condition of your blower sounds normal.  Blower lobes do not stay clean and collect oil fumes.  They also get scratches.  If you really have that much play in the lobes it is probably the blower drive and/or shaft.  Also, if you take the blower off you should rebuild the governor, and you will have to "run the rack" on the injectors.  All of this is not for a beginner.

--Geoff
General Diesel Serrvice
Prescott, AZ

[JohnEd]

Other than the "1/8-1/4 turn" of the rotors the visual condition of your blower sounds normal.  Blower lobes do not stay clean and collect oil fumes. 

Firstly....I am not agrueing with anything you have said....just in case it might sound so.  I have been told that the blower seals are a weak link and that triggering the emergency shut down will suck the seals in and ruin them,  Regardless if all that is true....how can I tell if the seal is bad and howw much oil is too much and where is the eposit normal?

They also get scratches. 

I have looked at a half dozen of these blowers and ALL had scratches ad gouges so dep that I thought the engine must have injested gravel.  I was told, as you have said, thsat that is "normal".   What is it that scratches the rotors?


If you really have that much play in the lobes it is probably the blower drive and/or shaft.  Also, if you take the blower off you should rebuild the governor, and you will have to "run the rack" on the injectors.  All of this is not for a beginner.

There are beginners and then there are beginners.  I am a beginner and I say that without reservation.  I also blueprint my engines and rebuild my own trans and hydraulics.  Is it that you need information that is not in the book?  Do you need the support of a Master Mechanic?  Are their tools and equip that are rare or out of the reach of the amateur mechanic?  I was once told that to run the rack that you need more than two thousand dollars worth of "gauges".  I asked my DD dealer and, baring his not understanding my question, he said "you only need the gauge associated with the injector your engine is equipped with."  He mentioned that you need long feelers gauges but you can make those or buy the DD items for modest money.  Was the DD rep/mech correct?  What do you think a learning mech might have to invest to run the rack on a specific engine with a certain size injector?  I am asking you because you are expert in these matters and you opinion matters.

--Geoff
General Diesel Serrvice
Prescott, AZ

I think many are interested in the whys and wherefores that rule our involvement...no joke or sarcasm in that statement.


John

[bevans6]

I looked at what was involved in pulling the blower, and the stopping point for  me was having to completely reset the governor.  I didn't think you could take the blower off and put it back on without being able to set up the governor from scratch.  I've been building race engines, transmissions, cars for 25 years, but I wasn't about to try that with nothing but a manual and a baseball cap (so I didn't tear my little hair out).

"Running the rack" is a horse of a different colour.  First off you have to decide what you mean by running the rack.  I think that doing it right starts with going right through the governor, so see the comment above.  But if all want to do is set the valve lash and the injector timing, which may be all you need to do, then anyone who has set the valves on a push-rod Chevy could do it, with a couple of wrenches, feeler gauges and the timing gauge, which costs $21.95 ( I've recently bought two of them).  If you had a lathe and some half inch bar stock, an injector timing gauge of your choice is no more than a half hour away.  But - there are a number of steps in the middle - maybe you have to change a few injectors, maybe you have to synchronize the racks on a Vee engine, maybe you have to set the idle speed and the buffer switch, maybe you have to change the no load rev limiter.  On a MUI engine there is a lot of mechanical magic going on in there, and you really do need to understand it before you mess with it.

Now, hopefully in the next month or two I will get a nice little 6V-71 that I can take a look at and mess with, and maybe I will be able to figure out what makes them tick.  My motto is someone figured it out once, I can do it twice!  But I will think long and hard before I take my running engine apart and see what makes IT tick!

Brian

[kyle4501]

I'm in the middle of disassembling an old 8V71. I had a friend (retired 2-stroke mechanic) come over to help when I started. He described the tune up process & pointed out what had to be done, some with the engine running wide open!

I agree with Geoff & Brian, that ain't a job I'll undertake as a beginner.

For the purposes of tuning a 2-stroke, a beginner is anyone who hasn't actively participated in tuning one before.

(edited to add)

[JohnEd]

On a MUI engine there is a lot of mechanical magic going on in there, and you really do need to understand it before you mess with it.

Now, hopefully in the next month or two I will get a nice little 6V-71 that I can take a look at and mess with, and maybe I will be able to figure out what makes them tick.  My motto is someone figured it out once, I can do it twice!  But I will think long and hard before I take my running engine apart and see what makes IT tick!

Brian

I like your style.  I would be following your path and Kyle has some good observations on the definition of a beginner.  Right after reading the book for a good long while the first thing I reach for is the telephone to call a knowledgeable "old Salt" and get some OJT.

It sometimes takes a while to distinguish between pluck and foolish arrogance.

Hope we can see some pictures of this adventure.  My money is on you Brian....not the machine.

John

[Geoff]

"I am asking you because you are expert in these matters and you opinion matters."


Humm?  Everything I said in my previous post is correct.  And yes to the other information you received-- You need special tools and feeler gauges to set up a blower.  The thing about 2-stroke Detroits is that it DOES take a few times to get the feel for what you are doing. 

--Geoff
General Diesel Service
Prescott, AZ

[RJ]

T-

I totally agree with Geoff -

"The thing about 2-stroke Detroits is that it DOES take a few times to get the feel for what you are doing." 

I'll be the first to admit that I haven't turned a major wrench on a 2-stroke, but spent a lot of time wrenching on Corvairs back in the late 60's and early 70's.

Like any engine, that little flat six had it's own quirks which could drive you batty, yet became a cinch once you'd practiced awhile and figured out how it's done.  Synchronizing the carbs, adjusting the valves or getting the fan belt tension correct are three of the quirks that come to mind, for example.

It all boils down to the old adage:

"You cannot teach experience!"


FWIW & HTH. . .




PS to Geoff:  Welcome back!! 

[lostagain]

I am a self described backyard, shade tree mechanic. But I tore apart my 4-71 and rebuilt it to turbo specs. And have tuned it and ran the rack 2 or 3 times. It is certainly not magic or rocket surgery. You need the DD service manual. Read it untill you understand what is coming. Then follow it to the letter. I have some bent feeler gauges and inj. timing gauges. If you didn't have the gauges, you could use the tail of a micrometer, or build one like Brian said. I have had the governor drive with fly weights, and governor itself apart a few times, and the same applies about understanding the procedure. "Getting the feel of it" aspect is important too, but it comes with doing it a few times. I also have a couple of trusted good DD mechanics that I call for advice when I need. What I do takes time, but it is part of the hobby. I enjoy it as much as driving and camping in it. You can't beat the good feeling of taking the bus out after a repair or tune up that you've done yourself. Sure is better than paying some apprentice $120/hr to learn how.

JC

[JohnEd]

Would it seem self contradictory if I were to say that I agree with Geoff and JR and JC.  Well, I do and it isn't a contradiction to me.

Back in the day I was the "go to guy", among shade trees, for rebuilding and tuning the Strombergs and reps.  Considering the absolute messes that I straightened out for friends and friends of friends of friends on Sat and Sun afternoons you would think that working with those carbs WAS IN FACT ROCKET SCIENCE.  A lot of what I did was to correct what had been done by shops in SD and LA.  Da BOOK said "a major tune up, including valve lash, is required prior to attempting to adjust the carbs".  Few read and understood the critical import of that prelim step and I did ONLY after ignoring it the first time (and last) I tried to sync my carbs.  And if the guy couldn't bring his "book" and his Syn Gauge and use them under supervision then I sent them to the only shop in town that had the reputation of being able to "do the carbs right".  An appointment there and $700 would solve the problem with your carbs and that was in 75 and he had a waiting list that was full of people that had tried several other professional shops.  I know cause I talked with them at the races and on Sat and Sun.  "but Teach a man to fish........"

I agree with everything that was said....almost entirely.  Thank you for sharing.  Especially "You can't beat the good feeling of taking the bus out after a repair or tune up that you've done yourself. Sure is better than paying some apprentice $120/hr to learn how." Thanks JC.

John