O.T. CUMMINGS ENGINE FUEL PUMP

Just had a neighbor ( young fellow) come over and ask me something and I THINK I told him right but need some renforcment from some of the knowlegable folks here. 1978 ih Heavy truck with 855 cummings about a 350 small cam I am guessing. His engine mounted air compressor went out. As most of you know the fuel supply pump is monuted ON THE REAR of the compressor. Questions >>> is the compressor coupling or compresor in any way timed to the drive on the front of the engine or is it just pull it out and put it back?

I couldn't say for sure on a CUMMINGS engine as I have never seen one but on a CUMMINS 855 engine the pump just supplies fuel the timing is done by another lobe on the camshaft through a pushrod to the injector for each cylinder

That is my thoughts couldn see why it would need timing since the injector is cam oprated for each seperat cylinder. some one had told him the air compressor had to be timed and to look for marks on the gear.

if he has a single cyl air compressor it should be timed .
if he has a twin cyl air compressor it does not matter .
if it was not timed right dont worry there many running around not timed .
the timing marks to set them up are on the pully at the front of the moter ,if you can still read them .

Is he sure the compressor is junk or is it just a bad governor?

Single cylinder..Thru a rod. but no pulley this is mounted on the back side of the front timing cover and is gear driven..Can not find any marks on the drive gear or the gear that is left in the engine now.

I am confused. The only way to change the timing would be to get the cam out of time some how. The pump strictly provides pressure. The cam opens the injector up in the head. Some one correct me if I am wrong. LarryT

if you do not take the assec drive off just put the compressor on timing mark are on the pulley A B C on front of the engine, if you get the pulley in a different place it will run but the next time you run a over head it might be a little tuff

If you pull the compressor from the assy. drive, but leave the assy drive on the engine, you will have no problems with the timing marks on the pulley. It has been a long time, but It seems like time to pull out the specialty wrenches when un- bolting the compressor.
Tim in OR

Hey JM, I"ve only worked on one 855 over the years but it appears like as long as the accessory drive is allowed to stay in place and just the compresso/fuel pump is pulled it shouldn"t be that big of a deal to get everything back right. It looks like all that there is is a splined connection between the omoressor and the drive assembly. That said, this is the proceedure straight from an 855 service manual. The first proceedure is used to get the accessory drive assembly in time when building the engine as it shows the timing marks lining up with the front cover off. I doubt this proceedure will be needed but here is is anyways.----------Bar engine to NO1 cylinder, TDC (firing stroke), continue to rotate 90 degrees ATC. In this position the two center punch marks on the drive gear will mesh/index with the two dash marks on the camshaft gear. This timing is required so the external timing marks on the accessory drive pulley will be properly aligned with the timing mark on the gear case to show valve and injector adjustment positions. Keyway of drive shaft will be at the top. Secure drive to cylinder block. ------------Proceedure #2. This for actually installing the Air compressor. Based on step one it looks like you need to time the engine first for this to work out right. That said here is the sequence listed in the book.-------For balance of the engine and air compressor reciprocating force the coupling driven air compressor must be timed to the engine firing order. 1-Bar engine to "A" or the "1-6" valve set mark. 2-Rotate air compressor crankshaft so timing mark or male splined coupling hald keyway will be pointing at "9:30 o"clock" when looking at coupling end of compressor. 3-assemble splined coupling to air compressor drive shaft. 4-With a new gasket in place install air compressor to accessory drive housing. Tighten capscrews to 40-45 ft lbs torque.

If you can't get the name of the company correct that was started by Clessie CUMMINS what is the use of the rest of your post???

And, NO, there's NO need to time the IP on an engine with Cummins PT fuel system!

(But I'll guess blowhard NCWAYNE can type about 5000 words to get to that point!)
For those of you who need help with spelling the name of the company...

DAMN, wayne... why do you post the incessant BLATHER about stuff you know NOTHING about? I guess you just get a thrill from tickling the keyboard with your fingers!

The accessory drive timing marks are used to "run the rack" and are NOT needed to reinstall the IP which is NOT timed to the engine.

You are correct,if it is a single cylinder compressor (Cummins type) it should be timed,If it is a two cylinder compressor (B+W Tu-Flo)it can be installed on any spline.

I've never done much around 855's... but as I understand it, there are timing marks on that drive and you ~should~ make an attempt to get things set correctly FOR ONE REASON. If some poor bugger has to go doing a tuneup on the overhead at some point in time... I believe he's gonna need those marks in the right place... or it will at least make his life easier.
As far as running of the engine is concerned... No, the timing marks make no difference. The fuel pump is not timed and I don't beleive the air compressor needs timing either. Cummins PT fuel pumps are nothing more than a gear drive pressure pump that supplies pressure to the injectors. The injectors handle fuel timing on a Cummins... and metering is done by a controlled orifice in the injector and varied by the pressure supplied by the pump...

Rod

Alright I am a Cummins mechanic.You dont need to worry about timing THE COMPRESSOR unless its a one cylinder compressor then you should time it.It tells you in NCWaynes post.If you are removing the ACCESSORY DRIVE with the compressor because you cant get the back bolt out,they make a wrench for that.If you do remove the acccessory drive,you have to time the accessory drive to the marks on the cam gear,like it says in NCWaynes post.You turn the engine and align the timing mark where it says by the pointer on the front cover to the right place on the accessory drive pulley,which is also where you turn the engine over with a socket or a turning tool on the accessory drive pulley.
IF YOU TAKE THE ACCESSORY DRIVE OFF OF THE ENGINE IT HAS TO BE TIMED.THERE IS A PLUG IN THE FRONT COVER BEHIND THE ACCESSORY DRIVE PULLEY.TAKE THE PLUG OUT,TURN THE ENGINE UNTIL THE TIMING MARKS LINE UP LIKE IT SAYS IN NCWaynes post by looking though the hole where the plug was in the front cover.Thats after you get the pulley(which you need a puller for) off and the plug out of the front cover.Then you will have to turn the engine some way,probably with a helper on the crankshaft and you watching through the hole until you see the punch marks on the accessory drive line up between the two lines on the cam gear,then take the several bolts out that hold the accessory drive to the engine and pull the whole thing,accessory drive,air compressor,fuel pump off at one time after unhooking all of the lines and brackets from the air compressor and fuel pump.Then you can replace the air compressor and fix the accessory drive on your work bench if needed.Then put it back together making sure to get the two dots between the two lines looking through the hole in the front cover.I always painted a line on my gear where the center punch marks were with white out or something so it was easier to see because the shop I worked in had no windows and was dark all the time.
Its hard to get to that back bolt on the compressor if you dont have a bent 5/8ths wrench,called an obstruction wrench or starter wrench,its real hard.You can buy a wrench from Snap On made for that,or make a wrench by heating up a long 5/8ths and bending it to a u shape.Then its a lot easier to get that back bolt out.If it had a bracket on there to hold the back of the compressor,put it back on because it will help hold it on there.All of that stuff together is kinda heavy and that bracket helps support it.
If you leave the accessory drive on the engine,you only have to take 4 bolts out of the compressor and replace it.THAT INCLUDES THE VERY HARD TO GET BACK BOLT that you need a bent wrench for.
If this isnt enough,ask more questions and Ill answer if I see any.There is a coupler with teeth in it that has to go between the compressor and the accessory drive.Plus there is a rubber piece that goes between the fuel pump and the end of the air compressor.Old as that truck is the rubber thing could have broke and fell out years ago and now might have the piece on the fuel pump wore out.Just a possibility.Newer drive pieces are made of something stronger and it could have been changed.That piece is not very expensive and needs to be replaced especially if its an old rubber type.

You know BOB, what a smart a$$ed comment, from someone that doesn't know what their talking about, to make, and for what reason??? The man asked a question and out of all of the posts made in reply saying this or that I am the only one that actually took the time to consult an actual service manual and give him factory correct information. If that makes me a "blow hard" then so be it. At least I'm blowing correct informatin his way and I don't have to worry about whether the information I give causes someone to screw up something. As a real mechanic that is something I run into all the time, people giving advice when they know nothing, or worse just think they know something. Usually when said advice is followed is when I get called to repair the damage caused. If I did that myself I wouldn't have been in business as long as I have.............So, when you learn how to read a factory manual you'll see that the compressor drive is in fact timed to the engine, and then the compressor timed to it. As the manual more or less states it times the forces created by the compressor to those created by the engine. Basically the opposing forces help cancel each other out and reduce vibration.

So, quit your blowing as it seems it's actually you that doesn't know what your talking about....or would you care to call Cummins and tell them their factory service manual is wrong????? Enough said..................

Hey Bob.Knock it off.He did better than you.I dont know what is wrong with you but he had a manual and wrote what it said and it was right.You however blabbed something that was only irritating and didnt answer the question.I would rather see a 5000 word answer to a one sentence cut down of somebody any day.
Plus this happens on here all the time.You put some crap up here that doesnt answer the question then gripe when somebody does answer it.Thats real good?
The only thing wrong with NCWaynes post was it didnt tell enough.

(quoted from post at 00:05:28 12/31/10) If you can't get the name of the company correct that was started by Clessie CUMMINS what is the use of the rest of your post???

And, NO, there's NO need to time the IP on an engine with Cummins PT fuel system!

(But I'll guess blowhard NCWAYNE can type about 5000 words to get to that point!)
For those of you who need help with spelling the name of the company...

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This clown has some nerve calling anyone a blowhard!

Thanks to all for the INFORMATION He did pull the acc drive and mid day today got it fired up.
Made a 65 mile trip so maybe he got it right..Again thanks for all the info.. that is what I love about this board two sides to ever question.. If you don,t believe it the real one I love to read is WHAT TO USE FOR REAR WHEEL BALLAST....Any way thanks.. guys. and whatever have a good new years. We will all be here tomorrow.. just a year older..

Yeah, Larry, you and I are CORRECT, the compressor and IP don't need to be timed, but NC and T40 NEVER let the facts get in the way of a bunch of BS.

(quoted from post at 00:15:04 01/01/11) Yeah, Larry, you and I are CORRECT, the compressor and IP don't need to be timed, but NC and T40 NEVER let the facts get in the way of a bunch of BS.

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Bob & Larry, read NCWayne's post again.

For [b:0cc9952625]balance of the engine and air compressor reciprocating force[/b:0cc9952625] the coupling driven air compressor must be timed to the engine firing order.

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It isn't hard to tell the real mechanics from the "slap it together and if it runs its right" mechanics.