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"new" motor not up to scratch....

Started by scraf, 24 September 2008, 05:43 AM

scraf

The 450 SEL has just had a new motor installed by a friend of mine, the original motor was US spec, the new motor Euro spec. Technically, if I understand it right, I should be getting more oomph, due to higher compression and no catalizator type stuff on the exhaust system....

However, aside form running very nicely it is  lacking some grunt. With the old motor I could make the whole car twist just by revving the engine, and take off in gravel showeriring stones behind me.

Not anymore, it so sluggish getting up to 2500 revs, that I originnally though it was taking off in second. Once it hits 2500 it's business as usual until I hit,er, 160 kmh, when it feels like it's pulling back, it fact backing off the pedal at that speed makes it feel free'er.

We're thinking maybe timing as it's running on lpg ( don't really want to talk about how it's running on petrol at the moment ), but being a K-tronic it doesn't have any points, so must we use a stroboscope to set the timing ? We can of course mark the original position and try fiddling....

..... but anyways, it a little frustrating after a lot of work transplanting the motor to have her not running sweetly. Any thoughts or suggestions most welcomely accepted, especially regarding possible issues due to the US >> Euro switch.

TJ 450

You will definitely need to set the ignition timing and you should certainly renew the timing chain/tensioner/rails as well if it hasn't been done. How is the compression? You should check everything. Was the engine tested beforehand, or in an unknown state?  :)

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

scraf

... secondhand from a dedicated Mercedes scrapyard/dealer, supposedly low milage, one month guarentee.

s class

I think you have K-jet fuelling issues.  Based on your comment that at high speeds, the engine is happier if you lift off slightly.  You need to measure the control and system pressures. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

Related to that - the WURs on US and euro engines are not the same, neither are the valve timing, ignition timing specs. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

scraf

Quote from: s class on 24 September 2008, 06:54 AM
Related to that - the WURs on US and euro engines are not the same,

Um, WUR ??

Quote from: s class on 24 September 2008, 06:54 AM
............. neither are the valve timing, ignition timing specs. 

I was looking for ignition timing details from the library and saw the valve timing stuff, is "valve timing" similar or even another way of describing setting the tappets ? Sorry for the layman's queries, but the ball in is another court mechanical wise on this one, I'm just trying to help my mechanic garner whatever info we can.

Quote from: Michel on 24 September 2008, 08:36 AM
Not to mention that running on LPG will result in a noticeable loss of power

That is a constant that hasn't been changed during the surgery.

oscar

Quote from: scraf on 24 September 2008, 12:18 PM

I was looking for ignition timing details from the library and saw the valve timing stuff, is "valve timing" similar or even another way of describing setting the tappets ? Sorry for the layman's queries, but the ball in is another court mechanical wise on this one, I'm just trying to help my mechanic garner whatever info we can.


No, ignition timing is separate, it controls when the spark occurs.  If your ignition is set too retarded, it will lack power.  Whether you've used the original distributor, or the distrubutor that came with the replacement engine, you'll need to check the timing with a stroboscope.  Set it at top dead centre to start off with, then try 5 deg before top dead centre, see if either makes a difference to what it was like when you first drove this engine. 

What is the engine number of the replacement?  I'll have a look what the timing should be.


1973 350SE, my first & fave

scraf

Sorry oscar, but I was not completely clear in my query.

What I would like to know is if setting the "valve timing" is akin to "setting the tappets". If so I think the Haynes manual that my mechanic has will cover all the bases, if not I shall print out the relative stuff from the library. Well actually I should print out the library stuff for goor measure anyway.

Big big shame if we have to do valve adjustments at this stage of the game with everything back in it's place as opposed to the motor sitting on a pallet in the workshop, and then, thinking about it, he said he had done the tappets, or at least checked them.

John Hubertz

valve timing i believe is a function of timing chains and their stretch/original installation adjustment (I think they only can be altered by placing the chains forward or backwards by a cog on the cam gears.

I've heard there are huge differences in low vs high end torque w this adjustment - somewhere on this forum I believe.
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

oscar

Sorry scraf, now that I look again, I think I misread your question.  But valve timing is as John says.  It's the position of the cam in relation to the crankshaft and can be changed deliberately by skipping a tooth on the camshaft gear or placing an offset woodruff key onto the camshaft gear to artificially rotate it a few degrees either way.  The valve timing can also be inadvertently changed when timing chain stretch occurs. 

Tappet adjustment is different.  It brings the rocker arm and therefore valve either closer to or further away from the camshaft lobes.  Further away means you get noisy ticking tappets and the valves open later and close sooner therefore are open for a shorter time.  Closer valves means quiter tappets and optimal longer opening duration of the valves.

But back to my other post.  Check the ignition timing anyway. If there's way too much retard you'll get the lack of power you're experiencing.
1973 350SE, my first & fave

WGB

Timing chain stretch will drop off low low end power as will poor ignitin timing.

Make sure vacuum advance and retard lines are connected to their respective sources and that they are connected the correct way around on the distributor.
Assuming it is a K-jet Euro 450 - Using a timing light check that the timing is set at 0 degrees with the engine idling and the aircon turned off and check that the ignition advances and retards when the engine is revved in case of a punctured advance/retard diaphragm or seized distributor centrifugl advance.

WUR - M-B part no for a post September 1977 Euro should be 000 070 15 62 Bosch No 0 438 140 056

Bill

s class

THanks Bill for the WUR numbers.  OTOH, if he is running LPG only, would that not bypass the WUR and other k-jet components? 

If you have changed from US to euro engines, your compression ratio is different, and the whole LPG setup will be altered. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

scraf

Quote from: s class on 25 September 2008, 01:54 PM
If you have changed from US to euro engines, your compression ratio is different, and the whole LPG setup will be altered. 

Sorry I haven't had enough time to go through all the well appreciated answers to this thread, but that last comment makes me think that a quick trip to the place that ( recently ) installed my lpg system for a tune up wouldn't be such a bad idea. Just about the right distance for a test run after tweaking the ignition timing as it goes.

scraf

Ignition tweaked, ( by feel ) and the car has it's grunt back !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Still wants to hold back at 160 kmh, but that's another tweak, shouldn't be driving that fast anyway.

Imagine this .................  :) .... 100x bigger, I'd almost forgotten how much I love my car.

oscar

Great stuff scraf!! 

Now what about the other engine - was it on LPG and what was the fastest you could get it to?  I remember you posting about a fast trip to Germany was it?  I'm not sure what else to look at if there's still a difference between top speed of both motors.  Could be compression differences or a bunch of other things.
1973 350SE, my first & fave