671 inline engines

[artvonne]

   Looking at 4104's, there are references to high and low blocks. What does this mean, and how do you tell them apart? Does it make a difference in which head will fit?

  There is an 04 for sale that supposedly needs a cylinder head. It has a 4 valve head on it now, will a 2 valve head fit? I dont have any working knowledge on these engines, I dont even have a manual to look at. Im just trying to figure out if I can get it running good enough to drive it home, about 1100 miles, I could deal with making it right later on.

  How much does the head weigh? I assume its too heavy to lift by yourself, but could two guys pick it up off the block, or set it back down on the block??

  This one will probably fall through, the logistics are rather difficult for me. but the questions would still be helpful, if not now, maybe down the road somewhere.

  Also, if your building up an engine, what would need to be done to an NA engine to turbo it? And, if you found a decent right hand engine, what needs to be done to make it a left hand engine? I was told once that you need to flip the engine end for end, flip the crank, and move the gears and end housings end for end? Someone else said no, you only need to flip the cam and some gears??? I think the first guy was right, but what do I know.

[TomC]

I don't believe you'll find many low blocks anymore.  They have small oval inspection ports and not as good cooling.  The high blocks have the six squarish air box inspection ports, and have better cooling passages inside the block.  Any 6 cylinder head will work on either.

Two can lift the cylinder head off and on-although it is still heavy even for two.

The NA block has 18.7 to one compression-some with trunk one piece pistons, but if the engine was overhauled within the last 15 years or so, it will have two piece pistons (iron crown, aluminum skirt).  The turbo has 17 to one compression-different pistons (although I'm running 18.7 pistons on my turbo).  Also to go to turbocharging-change the injectors to N80's (300hp and 900lb/ft torque), add a bypass valve to the blower (it opens with turbo boost to equalize the pressure on either side of the blower thus making the blower free wheel with little horsepower loss), add air to air intercooling, bigger radiator, bigger muffler and air cleaner.

To reverse rotation, flip both cams, change the idler gear to the other side, and install a new oil.  Pretty easy actually.  Good Luck, TomC

[cody]

I was going to say turn the bus around and reinstall the engine, but then I figured that would be a smart a$$ comment and not appropriate for the dfiscussion so I'm not going to say it. 

[artvonne]

Two can lift the cylinder head off and on-although it is still heavy even for two.

To reverse rotation, flip both cams, change the idler gear to the other side, and install a new oil.  Pretty easy actually.  Good Luck, TomC

   How heavy?  for two guys that can bench 400 pounds, or two normal old guys? Just trying to get a good picture.

   I assume you meant to add "pump", in your statement above "intall a new oil"? Interesting that its really that simple, lots easier than turning the Bus around and reinstalling the engine, eh Cody?


   I am concerned about adding too much power to the 4104 gearbox. RJ has pointed out that the 871 blew out the bevel gears, so they moved them ahead of the gearbox on the 871 V drives. Although I would think a low boost smog turbo and keep the HC pistons should be ok.

  On the subject of gearboxes, is the spicer 4 and 5 speed the same basic box? If you could adapt a 5 speed,might it be possible to find a gearbox with granny low?

[Ncbob]

Why in the world would anyone wish to change out a 4 valve head to a 2 valve? The whole reason for the 4 valves was valve cooling and better breathing. And, while I don't mean to split hairs with Tom C, one is a camshaft and the other is called a balance shaft. You can't run the Roots blower backward and expect that the engine will run and too it won't start with the original starter.

Something tells me that this might not be the bus you would really want to start with. There are good values out there. My advice...keep looking.

NCbob

[artvonne]

Why in the world would anyone wish to change out a 4 valve head to a 2 valve? The whole reason for the 4 valves was valve cooling and better breathing. You can't run the Roots blower backward and expect that the engine will run and too it won't start with the original starter.

Something tells me that this might not be the bus you would really want to start with. There are good values out there. My advice...keep looking.

NCbob

  Ive been told by numerous sources that the original 2 valve heads are almost indestructable, and that the 4 valves are prone to cracking. This particular Bus has a bad 4 valve head. I'll admit i dont know squat myself, so I have to listen to others and decide for myself. I will say I wasnt stupid enough not to consider the starter and blower, but I doubt Tom left it out of the discussion for any other reason than oversight. But 2 valve or 4 valve, how much will it really matter? Probably very liitle with a turbo.

  Balance shafts in a 671?

  I wonder what your advice would be if the head blew on me 1100 miles from home? Walk away and look for another Bus? I have never been afraid of a non runner if the price was reasonable.

[Kevin]

Art,

While my knowledge is quite limited, I believe another advantage of the 4-valve head is that one can add the highly desirable "Jacob" engine brake. That is the reason the PO changed out the cylinder head on my '04.

I drive my coach in mountainous areas almost exclusively. Once, the microswitch (located on the governor housing - activates the engine brake) attachment screws loosened and the brake quit working. I was descending the pass from Las Vegas to Pahrump, Nevada and boy, did I miss the engine brake!

(I phoned Bernie of Bernhardt's and he graciously described what to look for. A simple adjustment with a flat-blade screw driver put me back in business).

Anyway, if it's true that one must convert to the 4-valve head to install an engine brake, I highly recommend it. I've also heard that more power can be had, but I do not know if that is true.

I inquired for a long time for about optional transmissions for the 4104. Seems like you can have anything you like as long as it's a Spicer 4-speed or an Allison 3-speed auto. Never heard any discussion about a Spicer 5-speed, but I'm pretty sure it would have been done by now if possible, so I'm guessing not, dang-it!!!

[Ncbob]

Yea, a balance shaft m'friend. A V Configuration has two camshafts...one for each bank. In the in-line version the balance shaft is only there to carry rotation back to the accessory drive (on the back of the engine for necessities like the blower drive and the fuel pump or a compressor or a power steering pump or whatever the original configuration was for the engine.

It's not my intention to sound like a smart a$$ but at one time I was DD trained on all the seriies they had back then. Perhaps I'm familiar with engines long since out of production but am pretty knowledgeable about the whole DD line. Have to admit I can't answer much about the Series 50 or 60's but would sure line to have a 60 in my bus...but I doubt it would fit.

NCbob

[TomC]

If you're running N55 or N60 injectors,the 2 valve head works fine. The N65 or above injectors need the extra exhaust flow of the 4 valves to work-especially with a turbo engine.

NCBob is correct, both the oil pump and the starter have to be changed. 

When you flip the camshaft around, then change the idler gear to the other position, the blower will run in the correct rotation to run the engine. 

This was the beauty of these old 2 strokers. You could run with the blower on the right or left side, the head with the exhaust on the right or left side or any combination.  You could lay the engine on its' side, or even stand it straight up, and they run as happy as can be.  The same valve train and injectors was used whether it was a 3-71 or a 24V-71.  We will never see the likes of the Detroit 2 stroke engines versatility probably ever again.  Good Luck, TomC

[zubzub]

There are jakes out there for  6-71 with 2 valve heads...it's just harder to find them.

[artvonne]

Yea, a balance shaft m'friend. A V Configuration has two camshafts...one for each bank. In the in-line version the balance shaft is only there to carry rotation back to the accessory drive (on the back of the engine for necessities like the blower drive and the fuel pump or a compressor or a power steering pump or whatever the original configuration was for the engine.

NCbob

  I never knew they had abalance shaft, I always thought they were twin cam, shows what I know. Sure would be nice to find an engine manual, any available online?

  Somewhere that saying about being careful of the toes you step on today, comes to mind. Dont worry about coming across like a smart a$$. If it wernt for educated mechanics trying to steer noobs down the right path, we would all be screwed.

   So what IS the truth about the 4 valve head, is it more crack prone, more valve trouble, or is that BS? Which head would you head into Alaskan wilderness with? Jakes are highly desireable, but I would go without if it made the engine more durable.

[TomC]

Practically all 6-71's in buses have been changed out to 4 valve heads.  They perform better, with better fuel mileage.  They are tuff as long as you don't over heat the engine (much over 210 degrees).  I would feel 100% comfortable going into any wilderness with a 4 valve head (and I have when driving my truck with 8V-92TA) and would get Jakes installed also.  Installing Jakes on my bus was the first thing I did (along with bigger injectors, changing the rear end from 5.57 to 4.56, changing the front axle grease bearings to oil, and changing the bolts to accomodate my Budd type wheels [twin nut positioned]).  Good Luck, TomC

[artvonne]

  210 isnt very hot, at least in automotive experience. Is that considered overheating in a Bus/Truck?

[fe2_o3]

"Sure would be nice to find an engine manual, any available online?"
   I think I sent you a email about this. Let me know if it works...Cable

[luvrbus]

ZubZub the Jakes are the same for a 2 valve as the 4 valve head only difference is a 4 valve uses a bridge for the 4 valve head, on the 2 valve head it uses a cap 1 per cylinder  


good luck