King of Obsolete

1988 R Model Mack

15 posts in this topic

on buddy barry's 1988 r model mack, it has a miss at higher rpms. any ideas???

changed the fuel filters and did some basic checks. now i have to check valves and injectors.

thansk

KoO

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on buddy barry's 1988 r model mack, it has a miss at higher rpms. any ideas???

changed the fuel filters and did some basic checks. now i have to check valves and injectors.

thansk

KoO

Published Author

First off I would do a major tune up on the engine including fuel, air, and coolant filters, run the overhead, and a compression test both wet and dry. Some of this you have already performed. If the compression check does not yield results within about 15% of each other cylinder, it is time to pull the heads for gaskets and checkout of the heads/pistons/rings etc. I would send the pump and nozzels into the fuel shop for checkout and calibration also at this time. This can be a lot of work so a routine tune up is the first order of business.

A high rpm miss can be related to weak pump delivery, faulty injectors, sticking valves at high speed, broken, or weakend valve springs etc....

I lean on injector, or valve problems myself if the engine idles fine.

Rob

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hello,

I would not recommend a wet commpression test on a diesel engine..... They tend to want to run on that oil you squirt in the cylinder... kinda hard on the compression gauge.

Fred

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hello,

I would not recommend a wet commpression test on a diesel engine..... They tend to want to run on that oil you squirt in the cylinder... kinda hard on the compression gauge.

Fred

With all the injectors physically out of the engine?

Rob

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thansk for the quick reply guys. i have had not much to do with these macks. i only get to work on buddy barry's mack when he runs in to problems.

since it is a holiday in canada, i'll check under the valve cover on thursday. here is a picture of his mack.

thansk

KoO

Published Author

post-4140-1246475618_thumb.jpg

post-4140-1246475658_thumb.jpg

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i could not take it any longer and slipped out to buddy barry's shop and popped the valve cover off. then i ran the engine and it is the front 2 line on the pump that don't make much difference when the engine is running. so i when to the storage trailer and took the pump off the parts engine. on thursady i change the pumps and see if that makes a differnce. these pumps are like IH crawler pumps and just line up the marking gears (this has a flat gear)????

also how do you set the valves since the rocker arm has and adjust and so do the valves??? also how do you set the raocker arm that has the big end on it???

the tg on the engine says

E6-350 serial number 6W0161

valve setting intake .016 exhaust .024

on a cold motor.

also 3 days ago the phone tower here burnt to the ground so the nearest phoneis 300 kms away. they say it will be 2 weeks before we have phone services back plus, bank machines, interact, and internet. good thing i have my own high speed dish. the joys of living in the great white north.

thansk

KoO

Published Author

post-4140-1246489128_thumb.jpg

post-4140-1246489157_thumb.jpg

post-4140-1246489190_thumb.jpg

Edited by King of Obsolete

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i could not take it any longer and slipped out to buddy barry's shop and popped the valve cover off. then i ran the engine and it is the front 2 line on the pump that don't make much difference when the engine is running. so i when to the storage trailer and took the pump off the parts engine. on thursady i change the pumps and see if that makes a differnce. these pumps are like IH crawler pumps and just line up the marking gears (this has a flat gear)????

also how do you set the valves since the rocker arm has and adjust and so do the valves??? also how do you set the raocker arm that has the big end on it???

the tg on the engine says

E6-350 serial number 6W0161

valve setting intake .016 exhaust .024

on a cold motor.

also 3 days ago the phone tower here burnt to the ground so the nearest phoneis 300 kms away. they say it will be 2 weeks before we have phone services back plus, bank machines, interact, and internet. good thing i have my own high speed dish. the joys of living in the great white north.

thansk

KoO

Published Author

Hi there, I have never had the pump off of my E6-350 but I'm thinking that it does have a flat, or missing tooth on the drive gear to slide on one way only. I would not turn the engine over with the pump removed just in case.

To set the valves get yourself a service manual as it will explain the proceedure perfectly. You must have a way to "bar" the engine over by hand with either a breaker bar, or some way to turn the engine by hand to bring the cyliners that you are going to adjust the valves on to TDC. You then loosen the locknut of the rocker arm at the side opposite the valve stem bridge and adjust the clearance between the arm, and the valve stem bridge while pushing down on the back of the rocker arm to open the gap. Using a screwdriver to hold the adjusting screw in position, tighten the locknut and recheck your clearance to ensure you are still correct. Follow the firing order of the engine, (1,5,3,6,2,4) and adjust the valves in this order. Just bar the engine over till both rocker arms for the cylinder you want to adjust are loose with clearance. This is the area you need to watch closely. For instance turn the engine a little further than when you first notice one valve just stopping to move. If you don't go a little further than this point it is possible for you to be on the "ramp" of the cam lobe and not in the position the adjustment needs to made in. I'm only talking moving the crankshaft another inch or so from the point when one of the rocker arms stops moving. If you adjust your clearance while on the "ramp" of the cam, the operating clearance will be way off when the engine is running.

If you don't have access to a service manual I can scan the proceedure for you in a .pdf file. PM me your email address if you need it.

Rob

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thansk rob, i have no access or any service manual for this truck. i can't even get the pages faxed to me with no phone.can you email me at

info@kingofobsolete.ca

also include your snail mail and i'll send you a copy of my book for your troubles.

thansk

KoO

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thansk rob, i have no access or any service manual for this truck. i can't even get the pages faxed to me with no phone.can you email me at

info@kingofobsolete.ca

also include your snail mail and i'll send you a copy of my book for your troubles.

thansk

KoO

Published Author

Yes I can do that but it will be in the morning as my manuals are at work. This will give me something to do. I don't want to post it here because it is a memory hog and there is only so much space available to each member. If anyone else needs anything I've got access to they're welcome too.

Rob

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thansk, will be looking forward to it in the morning.

thansk

KoO

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With all the injectors physically out of the engine?

Rob

It sure will , It will fire one the cylinder you are checking, The oil is the fuel source and the compression is restored by installing the gauge. The istructor at diesel school has a compression gauge with the hose blown to bits and the gauge face all screwed up and he said thats what happens. He said the the flex hose kinda stood straight up like a snake and then poof. I would have never thought it would have done it, but it makes sence.

Fred

a.k.a. Morgan

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It sure will , It will fire one the cylinder you are checking, The oil is the fuel source and the compression is restored by installing the gauge. The istructor at diesel school has a compression gauge with the hose blown to bits and the gauge face all screwed up and he said thats what happens. He said the the flex hose kinda stood straight up like a snake and then poof. I would have never thought it would have done it, but it makes sence.

Fred

a.k.a. Morgan

That's news to me also. I've done several using ATF and never had an issue.

I'll remember that.

Rob

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thansk, will be looking forward to it in the morning.

thansk

KoO

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Sent the file.

Rob

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Hi there, I have never had the pump off of my E6-350 but I'm thinking that it does have a flat, or missing tooth on the drive gear to slide on one way only. I would not turn the engine over with the pump removed just in case.

To set the valves get yourself a service manual as it will explain the proceedure perfectly. You must have a way to "bar" the engine over by hand with either a breaker bar, or some way to turn the engine by hand to bring the cyliners that you are going to adjust the valves on to TDC. You then loosen the locknut of the rocker arm at the side opposite the valve stem bridge and adjust the clearance between the arm, and the valve stem bridge while pushing down on the back of the rocker arm to open the gap. Using a screwdriver to hold the adjusting screw in position, tighten the locknut and recheck your clearance to ensure you are still correct. Follow the firing order of the engine, (1,5,3,6,2,4) and adjust the valves in this order. Just bar the engine over till both rocker arms for the cylinder you want to adjust are loose with clearance. This is the area you need to watch closely. For instance turn the engine a little further than when you first notice one valve just stopping to move. If you don't go a little further than this point it is possible for you to be on the "ramp" of the cam lobe and not in the position the adjustment needs to made in. I'm only talking moving the crankshaft another inch or so from the point when one of the rocker arms stops moving. If you adjust your clearance while on the "ramp" of the cam, the operating clearance will be way off when the engine is running.

If you don't have access to a service manual I can scan the proceedure for you in a .pdf file. PM me your email address if you need it.

Rob

Rob, you have made a very good point about being sure that you are on the heel, or base circle of the cam before attempting to adjust the valves.

For that reason, the most accurate way to set the valves is during the overlap. It is hard however for some folks to wrap their mind around that idea. Although it is all old hat for you, it might not be so for everybody, so here is a little chart that I use to remind me where I am while running overhead. It represents the 720 degrees it takes to completely cycle any 4 cycle engine.

Mack or Cummins in line 6 both fire 120 degrees apart

1 5 3 first 360 degrees or top of the firing order

6 2 4 second 360 degrees or bottom of the firing order

When you look at the balancer it will be marked 1-6 5-2 3-4 . It does not matter where you start in the firing order. If for instance the timing pointer is at 5-2, with the valve covers removed look at the valves on 5 and 2. If you have a valve open on 2, then you are at TDC on 5, or just opposite, same deal. If you are on 5 adjust the valves and bar the engine over to 3, checking for an open valve on 4. A good idea is to mark each valve as you adjust them. a tire crayon or white out work for me. Someone who does this every day might not need a chart. The important thing is to know where you were if you have to walk away and come back later. Check behind yourself, the best mechanic's always do without thinking about it.

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I can't say that I've really ever looked at a balancer on any of my engines to ascertain if they are marked in degrees or anything. It is such an important operation and part of a good tune up that the familiarity is almost like my name to me. I had to think to explain it.

I did notice "Dynatard" solenoids on the pictured engine. I oversighted and the engine does have a "Dynatard" engine brake, now would be an opportune time to install a new set of rings and seals. Valve adjustment is very critical on those engines for the engine brake to work satisfactorily. In fact, I check my work twice when working with them.

Yes, base circle or valve overlap, (times when all valves are closed) in the cylinder you want to adjust is very critical. Most four stroke engine have a relatively slow valve opening and closing due to the ramp of the camshaft design. This is to promote a wide torque band of operation and smooth idle. This also increases the physical size of the ramp and lessens valve overlap "window" in which you need to work within. I've made the mistake of adjusting in the incorrect area and had to completely tear my work back down to re-repair something that never should have happened.

Persons that have been around/built high performance engines know the difference in camshaft profiles just at a casual glance. I used to regrind and custom grind camshafts on a special grinder many moons ago.......

Most times with the exception of bashing my head, I learn from past mistakes to not make them again.

Rob

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