Engine set-up advise

[JohnEd]

PVCCES doesn't mention that he lives in Alaska.  The lower compression pistons are "stock" on the 8V71 TA and T 92 series.  You are not building a hot rod or breaking new ground in any way.  Tom is right about the starting being harder but on a fresh rebuild you shouldn't see a problem. He is also right about the turbo using more fuel in spite of every test that has ever been done proving that it "could" get better MPG.  It is your foot sunk deep into HP you didn't used to have that ruins the MPG and if it wasn't fun and natural we all wouldn't do it.  On the open road using cruise control you should get close or better.

PVCCES drives a 4106 with a fresh 8V71N and it went through the streets of Eugene cornering like a Porsche and accelerating like a Corvette.  You follow my drift.  With his performance and MPG i would't be hot to turbo my rig either.  You are in a different boat with a 4L71N installed in a NON Aluminum framed GMC.

Yes the crown is closer to the top of the wrist pin,,,,as one way to do it.  Another is to dish the top of the piston or to increase the volume of cylinder head and another is to use a thicker head gasket like BMW does for bikes they sell in Africa and other third world countries.  You could also restroke the crank like the pros do.  When I blueprinted I gouged out some of the head and then "sunk" the valves by grinding the seats for a final adjust.  Dished pistons yield the worst results in a gas engine and I suspect a D also.

John

[VanTare]

I have no idea what John is trying to tell you but the combustion take places on top of the piston in a  DD diesel engine that is the purpose of the dish they do not have a combustion chamber in the head.Reading the book on a 2 stroke DD engine there is only .040 difference between the 19:! and the 17:1 the 19:1 being .040 deeper in the bowl   


David

[lostagain]

The shop I get my parts from is telling me they usually put the high comp. pistons in turbo rebuilds. Which is probably what I should do, unless someone gives a compelling reason for low comp.

I got the clutch out yesterday and it looks fine: 7/16th. The fly-wheel has surface cracks where it contacts the clutch, so I'll take it in to a shop for a look and possibly resurfacing. The fly-wheel housing won't come off unless the rear motor mounts are removed: big 1 1/2" bolts that did not want to budge last night. I'll probably use the angle grinder to cut the nuts off today. I am inching closer to the timing gears... It takes more time than one would think. Oh and the shop that has the head called yesterday saying they found antifreeze where there shouln't be. It is under pressure overnight and they will call me back today. Now I'm thinking I should maybe strip the block of all remaining parts and have it checked out too? Oh well, what's another couple of days...

Anyway, thanks for all the advise and moral support. I can really use it now.

JC

[JohnEd]

JC,

That shop you are dealing with either miss understood you or the other way around.  They have given you the exact opposite advice of what is called for.  I have exhausted whatever little credibility I might have on this subject and I expect you want/need more expert advice than I can give.  I "strongly urge" you to PM the professional/more knowledgeable Knuts on this board and run this conversation past them.  You are about to spend a LOT of money and do many hours of demanding labor and I know you know that.  Contact Don Fairchild or Dallas or Gumpy or TomC or PVCCES or BK or any of a host of others that easily distinguish themselves as knowledgeable on this board excluding VanTare/David.  I will speak with him off line by PM to sort out his erroneous advice.

Sincerely,

John

[lostagain]

John, don't worry, I will get advice from as many of the good mechanics as I can. I will have this engine as good as  possible. I have already invested a lot of hours dismantling it, and the parts aren't cheap, so I'll make sure the most suitable parts go into it.

I finally got the fly-wheel housing off and the timing turns out to be "standard" after all. Good, at least I know for sure now.

The coolant leak in my head (engine), turns out to be from an inj. tube. They are getting replaced as well as the valve guides, so all is well on that front now.

JC

[JohnEd]

On second thought, only part:

David,

You can easily "learn" what a combustion chamber is by Googling the term and selecting the reference for Wikipedia (http://en.wikipedia.org/wiki/Combustion_chamber)

In that reference it refers to the "direct injection diesel" as using the dish in the top of the piston as the combustion chamber.  It infers that only that particular version of internal combustion engine, and all of them in fact, is designed that way and that all others use the pocket machined/cast into the head plus the gasket thickness and piston dish and/or piston "sink". as the combustion chamber.  In spite of that being Wiki's official explanation, I doubted the validity of that info.  I contacted the west coast DD rep that is considered their resident expert on two cycle diesels, Dave Mueller.  Dave informed me that the "all" two stroke diesels have a flat head and use the dish in the piston as the "combustion chamber".  I asked about the Series 60 and he said that it has a pocket in the head and that pocket is the combustion chamber in that "direct injection" engine.  Seems WIKI is wrong on their point that "all direct injection engines use the pocket in the piston as the combustion chamber".  

Now that is a small point in the grand scheme of things but don't ya just luv it when that happens?  Me too.

John

[JohnEd]

JC,

Thank you for that update and the coolant leak loc is good news.  Good for you!

Your right about that....I was concerned for you and that I might have let you down in some way.

With a smaller displacement engine is it probable that you would slip the clutch moreso than with a biggie?  Is that scorching normal?  I know some of the 8V71 guys have opted for a heavy duty clutch and others have mentioned a dual disc unit.

Along the lines of the clutch, have you ever heard of letting the "high speed idle gov" start you out on a hill?  That yields minimal clutch slippage and sometimes makes a start possible.  People here get apoplectic at the mention of that but it just makes so much good sense to me.

Write often and long Amigo and good luck,

John

[lostagain]

All I can say about the flywheel being scorched and cracked is it must be from the POs abuse. I always start from a stop at iddle with my foot off the accel. pedal. The flywheel is probably 52 years old like the bus. I am taking it next week to a specialty shop in Calgary. We'll see what they say. I have 2 others off 4-71s, but they are different for different applications.

JC

[TomC]

I have seen many engines apart.  The statement that all direct injection diesel engines have flat heads and the combustion chamber in the head is completely true.  I have yet to see and direct injection head, including Series 60, with any kind of pocket or dish in it.  Now on my Mercedes-Benz with prechamber, yes it does have a pocket for the fuel charge to come out of the prechamber.  Just my 2¢.  Good Luck, Tomc

[Van]

Howdy,these are the top of my 692TA's pistons,the heads are flat.On another note,you guy's surely remember Luvrbus,Cifford's engine(8V92TA) boasts 500+HP with 19:1 pistons and 17lbs of boost and can pull away from most 60 series engines.fwiw. Van

[BG6]

I have the 4-71 DD out of my Courier 96 and I am doing a complere overhaul. I wanted to fix some messy oil leaks and pulled it out,

2-stroke Diesels don't leak oil.

They MARK THEIR TERRITORY.

[JohnEd]

TomC,

They did say that Dave Mueller is the "2 Stroke" expert.  Maybe he is all wet about the S60 series heads.  Can't argue with what you have seen, of course.  He did tell me that the 60 had pocket Chambers in the heads.....no kidding.  I haven't seen either engine torn down so I am going on what the most expert info is I can find.  Your on that list so I guess I now have two experts disagreeing with each other.  And, I don't imagine either of you are loosing sleep.  Me, on the other hand, I'm really anal on this stuff.

I'll call DD on this later today.  For what its worth,  I talk to these guys and when I have my answer they say something like "Is that all?" and "call back if you have more questions.  Happy to help."  You know, real disagreeable like up here in the Great Northwest.


Van,

I am surprised that the 92T has 19::1 and only 17 lbs of boost.  No wonder they say that you can boost it to over 600HP easily.  Is 19::1 standard?  I have read more than once that the 6V92 runs more than 25 PSI of boost....is that wrong?  From what I have read the 92 series uses identical parts in the 6 or 8 config so they should have the same specs for PSI boost and such....seem reasonable?  Also may not be true.

John

[Van]

John ,I myself am no expert,but 17:1 is the standard and so far as the 6v vs the 8v I believe they are mostly the same parts but are not identical in every respect .Fwiw you know me and I too have to rely on the experts here on the boards as well as the manual.I do know the marine engines are set up for 600hp + ,all I know is I want one LOL,have a great week end.


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[lostagain]

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[BG6]

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