Idiot Q on OM617 Vacuum Pump - Page 3 - PeachParts Mercedes-Benz Forum

Stretch · #31 12-09-2014, 01:12 AM

Quote:

Originally Posted by charmalu

Here is some good info in this thread on the vacuum pump.
Not sure if the answer you are looking for.

He mentions that the pump doesn`t produce vacuum all the time, when it reaches the set point, she lays back till the need for more vacuum is needed, sort of what VSTECH mentioned.

VACUUM PUMP FAILURE! Are you neglecting yours??

Charlie

I got bored one winter and did some silly experiments to see if that was the case

More than you are likely to ever want to know about OM61X piston vacuum pumps

I don't think it does that

koldstart · #32 12-09-2014, 01:57 AM

well, I would clearly call you an expert on the question. Are you saying that I would have an issue If I ran my vacuum pump to a reservoir to hold vacuum for shut off? My mind was at ease until you came along!

Stretch · #33 12-09-2014, 07:20 AM

Quote:

Originally Posted by koldstart

well, I would clearly call you an expert on the question. Are you saying that I would have an issue If I ran my vacuum pump to a reservoir to hold vacuum for shut off? My mind was at ease until you came along!

Who me?

I was responding to the bit I highlighted - well put in bold - in Charlie's post.

For just the shut off valve I'm sure an electric central locking pump would be more than sufficient. (I've said it before and it is probably getting tedious but) A blond in a passenger seat with a tube connected to the shut off valve is also a great modification to have...

If you are using vacuum for power brakes however that is another story - it is also made worse if you are using vacuum for shifting a Mercedes automatic transmission =>

Calling mach4, funola and JB3 for their insights (apologies to others who have also investigated this)

mach4 · #34 12-09-2014, 10:11 AM

First, don't worry about the vacuum pump. It will happily pump all day long regardless. Until someone actually shows me the "mechanism" that causes the pump to quit pumping when it reaches a particular level of vacuum, I'm with Stretch and consider that myth totally busted. . Pull the vacuum pump and inspect the bearings as a precaution, but then don't sweat it - they can be easily replaced though no one has definitively referenced recommended bearings other than "the highest quality 626 bearings you can find".

Rigging up a shutdown switch is trivial. I use one on my OM617->R107 swap. Just grab any old switchover valve or vacuum solenoid and plumb it in. (Just be aware if you use a solenoid you'll need to make a pinhole in the line to bleed off pressure or you won't be able to restart - ask if you need directions) Wire it to a momentary switch on the dash and you're done.

Since you don't have vacuum assisted brakes, EGR, locks or climate control, you can do without an engine driven vacuum pump, though this may not be wise. Most importantly this assumes that you do not use the MB auto transmission. If you do, you're screwed - the transmission has a VCV that constantly bleeds vacuum to mimic a gas engine's vacuum as a signal that affects the way the transmission shifts. (This fact is what killed my Arduino controlled electric vacuum pump project last year)

Removing the vacuum pump may not be a good idea. I'm starting to think that the pressure the vacuum pump spring puts on the back of the IP is needed to maintain the bushings. 617YOTA is dealing with that issue right now. I'm not asserting that as fact, only voicing a suspicion.

If you only need vacuum for shutdown, you won't need a reservoir. Just plumb a switchover valve to the vacuum shutdown.

Hope that helps.

funola · #35 12-09-2014, 10:39 AM

Quote:

Originally Posted by mach4

........

If you only need vacuum for shutdown, you won't need a reservoir. Just plumb a switchover valve to the vacuum shutdown.

Hope that helps.

I'd make it even simpler by plumbing the vacuum shutdown direct to a vacuum squeeze type fuel bleed bulb (available at marine supplies). That'd be unique.

koldstart · #36 12-09-2014, 02:21 PM

Ok, thanks for all the replies. I think I got a good idea of how I want to set it all up. I appreciate all of the input. Been around many forums, specifically ford / ranger forums when I did my first diesel swap into a ranger. Never seen such fast and helpful responses to questions. Thanks to all!

To anyone curious, here is my first diesel swap.. so you all not I'm serious about getting this done! (ranger+mitsubishi diesel.. not MB)

https://www.youtube.com/watch?v=jKdV51NhBA0&list=UUDVSUl4GFfmq7yC7aDhB8lg&index=12

Ford Ranger Diesel Project - Imgur

Ill be starting a new thread shortly. Thanks again for all the support and answers!

leathermang · #37 12-09-2014, 02:33 PM

We get paid according to the speed with which we provide the correct first answer...
How about just a nice aircraft quality CABLE to turn off the engine?...like I shut down my Ford tractor.

junqueyardjim · #38 12-09-2014, 02:44 PM

Quote:

Originally Posted by koldstart

I think that is what I wanted to see, if I blocked off the vacuum line from the pump it wouldn't hurt the internals of the pump trying to fight against it.

You can't stress or overload the MB vacuum pump. The tighter (and smaller) the system is the less the pump will work. What ruins or kills the vacuum pump is running it continually with a bad leak causing the system to be open. Then you would have low vacuum and an overworked system, and it would sooner then (rather then later) dump it's ball bearings into the chain galley. So, if you had a small, very tight system and a good working pump, it would quickly reach max vacuum and that same vacuum would hold the unit in a neutral position with no wear, no running until the vacuum dropped to a point where it would re-engage. That is the way the unit is built.

Lucas · #39 12-09-2014, 03:18 PM

Quote:

Originally Posted by leathermang

We get paid according to the speed with which we provide the correct first answer...
How about just a nice aircraft quality CABLE to turn off the engine?...like I shut down my Ford tractor.

That's what I'm saying! I want a cable shutoff and a red exhaust brake knob on the shifter of every diesel I own. Maybe an air horn and a cattle pusher.

And nice ranger. I love those swaps but I'm in California so not possible. In Central America, and prob other places, VW has a little diesel truck. Super cool.

OM617YOTA · #40 12-09-2014, 03:21 PM

Someone pull the check valve out of a working pump when it's not mounted on the motor and apply a vacuum from an outside source. Does it suck the piston closed against the spring at a vacuum level that these pumps will maintain?

junqueyardjim · #41 12-09-2014, 03:57 PM

Well there is some controversy here as to whether the system works as it is supposed to. I think I read about it in the Haynes manual. Pretty simple device I think, but it is hard to determine if it does work or if it is a crock. The follower wheel is supposed to lift off the "heart shaped" rail it runs on when vacuum is achieved. I would think that as with most of MB Engineering, it would work pretty good. They surely didn't want a pump design that would blow engines I am surprised that Stretch hasn't tested that out yet. Maybe we should encourage him to make that a winter project.

HEY STRETCH - WOULD YOU PLEASE CHECK IT OUT IF YOU CAN? Please?

koldstart · #42 12-09-2014, 06:43 PM

Quote:

Originally Posted by junqueyardjim

Well there is some controversy here as to whether the system works as it is supposed to. I think I read about it in the Haynes manual. Pretty simple device I think, but it is hard to determine if it does work or if it is a crock. The follower wheel is supposed to lift off the "heart shaped" rail it runs on when vacuum is achieved. I would think that as with most of MB Engineering, it would work pretty good. They surely didn't want a pump design that would blow engines I am surprised that Stretch hasn't tested that out yet. Maybe we should encourage him to make that a winter project.

HEY STRETCH - WOULD YOU PLEASE CHECK IT OUT IF YOU CAN? Please?

+1

mach4 · #43 12-09-2014, 07:09 PM

Sorry, I just don't buy the theory that the vacuum created by the pump is used to hold the piston of the vacuum pump away from the roller coaster rail. Sounds a little like perpetual motion machine theory to me. The pressure required to keep the piston away from the rail is always greater than the vacuum that can be produced by the pump.

And even if it did there would be moments in time where the follower bearing was in transition. During the transition time where it was only part-way pulled away from the rail it would be slamming into the rail on every rotation until it managed to get itself parked. Then when the vacuum dropped a bit, the follower would again begin to slam into the rail until vacuum dropped enough that it could again regain nice smooth contact with the rail.

It's kind of the opposite effect of valve float. The valves need to be in contact with the cam at all times or it beats itself to death in short order.

I've been wrong before and I reserve the right to be wrong again!

Stretch · #44 12-10-2014, 07:46 AM

Quote:

Originally Posted by junqueyardjim

Well there is some controversy here as to whether the system works as it is supposed to. I think I read about it in the Haynes manual. Pretty simple device I think, but it is hard to determine if it does work or if it is a crock. The follower wheel is supposed to lift off the "heart shaped" rail it runs on when vacuum is achieved. I would think that as with most of MB Engineering, it would work pretty good. They surely didn't want a pump design that would blow engines I am surprised that Stretch hasn't tested that out yet. Maybe we should encourage him to make that a winter project.

HEY STRETCH - WOULD YOU PLEASE CHECK IT OUT IF YOU CAN? Please?

Quote:

Originally Posted by koldstart

+1

I kind of have done that already.

If you look at post #13 here More than you are likely to ever want to know about OM61X piston vacuum pumps

I know it is a fair amount of information but essentially the "suck" due to vacuum on the piston is about 317N

This isn't the whole story though because the vacuum pump's bearings are whizzing up and down over the track surface of the timing device.

Sometimes the momentum of the weight of the piston and the moving parts in the vacuum pump will be pushing up against the timing device - but other times it will try to "get some air" as it tries to escape away from the timing device.

This whizzing up and down of these parts in the vacuum pump has a force associated with it. I've estimated that force in this graph

You can see that at idle - 800 rpm - you've got a tiny force due to the moving parts trying to push them away from the roller coaster track on the timing device. @800rpm I estimate it to be 20N

As you go faster the forces increase quite a bit - so this indicates that at certain engine speeds the moving parts might be able to skip over the top of the roller coaster track because the combined vacuum suck and the force of the moving parts trying to fling themselves away from the roller coaster track gets close to the maximum force the springs (that pushes the piston and bearings towards the timing device) can apply...

...the effect of speed plays a role in the behaviour of the system more than the constant "suck". If you just look at the combined measured forces of the two return springs and compare with the 317N vacuum force then the spring force is always more dominant.

For this reason I don't think that the vacuum suck parks the piston.

funola · #45 12-10-2014, 12:45 PM

I think Roy Hunter did some "parking" tests but did not post about it. I asked him about it a while ago and as I recall, he lost the camera where all the pics of the test were stored. Maybe Roy will chime in?