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W201 Compression figures
Topic Started: Tue Mar 17, 2009 9:35 pm (12,775 Views)
Johnboy Mac
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Diesels 2.0 & 2.5, compression ratio 22:1, new value 26-32bar, wear limit 18bar approx.

Petrol 1.8, 2.0, 2.6 compression ratio between 9:1 & 9.2:1, new value 10-12bar, wear limit 8.5bar approx.
2.3-16 compression ratio 10.5:1, new value 14-16bar, wear limit 12.5 approx.
2.5-16 compression ratio 9.7:1, new value 12-14bar, wear limit 10.5 approx.

Note:
Diesel max. permissible differences between individual cylinders 3.0bar.
Petrol max. permissible differences between individual cylinders 1.5bar.
(1 bar = 14.5 psi)

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merc190uk
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Nice one thanks

pinned B)
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Johnboy Mac
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merc190uk
Tue Mar 17, 2009 11:12 pm
Nice one thanks

pinned B)



No probs. I think worth having, it's not the be all & end of an engines condition but it's simple & cheap why to diagnoise a poss. fault.
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RobertE
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Excellent, Johnboy. And reassuring! I did the compressions on the new 2.5 the other day and got a very close average of 190 psi across the piece. The others are a tad lower (Bertha at 180 and Brunhilde at 170) but the highest mileage car has the highest compressions!
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Johnboy Mac
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RobertE
Wed Mar 18, 2009 9:05 am
but the highest mileage car has the highest compressions!


Robert, it's stange that as I don't know any technical reason for it compaired to the lower mileage cars all things being equal. You may recall I did mine @ 170k or something around that and got an average of 177psi (12.2bar) just hope it stay that way until I put funds aside for a rebuild.
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RobertE
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Yes, I know what you mean, mate - the bottom ends are clearly hugely strong, which is why they worked so well in competition, but the top end is always going to make me nervous; stories of cracked valves, etc., will wake me up at 3 a.m.! But really, I think they are utterly magnificent cars and worth starting a 'sinking fund' for. But I'm pleased about the compressions - I'm organising a leakdown test next week so that I can ask the right questions of the engine (s).
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manalishi
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Yikes!

Guys, is it possible to have compressions of 75 | 95 | 95 | 92 psi in a 2.3-16 and for the engine to work?

(hoping that Matt's equipment is misreading...!)
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jeremy
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manalishi
Fri Apr 3, 2009 12:13 pm
Yikes!

Guys, is it possible to have compressions of 75 | 95 | 95 | 92 psi in a 2.3-16 and for the engine to work?

(hoping that Matt's equipment is misreading...!)
Yikes , one is clearly down isn't it.? But having said that , think what it will be like once it's been attended to. ;)

Plenty of time to put it right.


Jeremy :evo2: :driver:
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manalishi
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Um... I was expecting figures closer to 180-190psi! Or am I doing something stupid with the 1bar=14.5psi maths?
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Will
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Yes, it's certainly possible for it to have those compression readings and run still. It would probably be difficult to start from cold, low on torque and mid range power though would probably feel more 'healthy' at high RPMs.

If it's not smoking like a trooper it almost certainly wants a head rebuild.

Will
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RobertE
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No, the arithmetic is right. Important to test on a warm/hot engine, though, and certainly worth using some sort of additive - Redex - Wynns - STP, whatever. You'll do no harm and if you have sticky piston rings or fouled-up valves it can only help.
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manalishi
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Seems the numbers aren't a mis-read, so the next step is that leakdown test. I gather from a search of old postings that it'll identify whether there's a big bill, or a HUGE bill in the offing...
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cossie connoisseur
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there can be only one ;-)
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yes your car will run but will is right regarding how it will run

one thing to add will be the the engine will vobrate a fair bit and you really wont be getting 100% out of her so if you drive one that is 100% then you will see and feel quite a difference.

tbh the costs can vary but the norm is up to £2000 for a rebuild so make sure the car is serviced regular to make it last and save up for a rebuild.

it nearly always the top end and very rarely the bottom end un less your really bad with servicing
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Matt
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Yes, im tending to think valve/s may be the issue here.

I shall do a leakdown test on it to confirm.
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cossie connoisseur
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there can be only one ;-)
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carbonising on the valvles will be the likely one
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Will
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And incorrect valve clearance. Bet the exhaust ones are tight!

Will
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manalishi
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Will - you may remember that I thought it was underwhelming to drive, so what you say above goes with that. Being an auto, it was harder to keep up in the top of the rev band, and there was a definite sense that - at low to moderate revs - it had no more 'go' in it than the 2.0 I used to have.
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Johnboy Mac
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Manalishi, if the engine ain't using much oil it fair to assume it's top end fault but that's a very rough guess.A leak down test should high light the actual fault.
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Will
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manalishi
Fri Apr 3, 2009 4:07 pm
Will - you may remember that I thought it was underwhelming to drive, so what you say above goes with that. Being an auto, it was harder to keep up in the top of the rev band, and there was a definite sense that - at low to moderate revs - it had no more 'go' in it than the 2.0 I used to have.
Hi Barry,

Yep, it all ties in with classic compression/top end issues :(

You do really need to sit down though and work out where you stand with this car - what you want out of it, what you're willing to spend on it etc.

A top end overhaul can get quite expensive depending on the condition of the head/valves, what needs doing etc.

A few cracked valves, and/or damaged/worn valve guides, plus the cost of parts (gaskets, bolts, seals etc) and the machining costs (skimming if needed, decoking, fitting the guides, lapping in the valves etc) Maybe (ideally) a new timing chain/tensioner too (would be criminal not to on a 2.3 unless it's very recent/new)

If you're paying for all of this to be done, I'd say you could be looking at anywhere between £1000-2000.

Will
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manalishi
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Will - Yes, after we have the results from the leakdown test, Matt and I have to have a long look at the £££ figures. With other jobs needing doing, too, it's looking a bit 50:50. Which is a shame after all the recent efforts on it.

Johnboy-IRL - I didn't run the car for long enough to know if it uses oil. I sent it to Matt pretty quickly after being underwhelmed by the driving experience.
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Johnboy Mac
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manalishi
Mon Apr 6, 2009 1:03 pm
Will - Yes, after we have the results from the leakdown test, Matt and I have to have a long look at the £££ figures. With other jobs needing doing, too, it's looking a bit 50:50. Which is a shame after all the recent efforts on it.

Johnboy-IRL - I didn't run the car for long enough to know if it uses oil. I sent it to Matt pretty quickly after being underwhelmed by the driving experience.


Manalishi, all the signs of top end rebuild required rather than anything wrong with bottom end, hope all works out o.k.
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cosser
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Hi Guys n Gals,
I got the compression tested a couple of months ago and I had approx
Cyl 1; 180
Cyl 2; 90
Cyl 3; 180
Cyl 4; 180

I've just bought an Am tech tester off ebay to do a wet test on number 2 to tell me if its rings or valves and I decided to test them all m first.To my confusion i got C1=4Bar C2=0Bar C3=4Bar C4= 3.8Bar...?????

I did a wet test on Number 2 and that crept up to 2 Bar which was what I was expecting but I'm stumped as to why these readings are so low...??

Could all of my rings (or worse) have gone bad so quickly,especially as I am rarely driving her since I found out about Cyl 2 in June,and even then I'm drivin like a priest..lol..!!

I warmed the car to 80 C unplugged the Green Ignition wire and took out the Fuel relay,and did each test with all of the plugs out.Am I doing something wrong...???

The weird thing is that the ratio between the cylinders is more or less the same in relation to the original test (Cyl 1,3,4 even and Cyl 2 down)...?????

Any Suggestions ....???

Cosser..!!
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RobertE
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Redex! I don't know which car you have, (I'm assuming it's a valver) but 3 out of four are very respectable, so don't panic. (You're obviously not). I'm starting to realise how much cr*p can build up and the effect that this can have on simple things like valve guides and seats.
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Martrider
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Longest build time in history?
Comma Detox i have found to make a huge difference on my 2.0ltr when used once a year. It's about £14.99 or £19.99 but works very very well in my experience. Get it at Hellfreuds.

I had a friend who i trust implicitly who worked for Comma - you couldn't believe a word she said about the products as she was a model dressed in lycra - but she did work for them for 5 years! lol
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RobertE
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There has been much talk of running Diesel engine oil for 5-600 miles before flushing it out and refilling with 'normal' oil. I know the M100 lads do this - it's something to do with detergents
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Johnboy Mac
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I think I've mentioned this here before. ATF is a great engine cleaner, drop the old oil and refill with ATF. Let run for 20/30mins at idle with the odd rev to 2000 only.
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cosser
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Thanks for the Advice guys,
I did post this problem in its own space in the Engine section under" strange compression test results" or something like it..lol...!!

Could you guys have a look at that post if you could and give me osome feedback...it would be much appreciated..!!..

Thanks Again.

Cosser..!!
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matsalleh76
Matsalleh76. RIP. Gone But Never Forgotten.
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Hint:
Do any compression test with the throttle WIDE open to eliminate any suction/vacuum influence on the numbers.

bobf.
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cosser
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Hi Guys,
Those low readings came from a dodgy Tester..!!I tested them with a good one and got better,but not great results.Details in the Strange compression test readings post on this thread..!!

Cosser..!!
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jags2.5-16
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Hey, silly blonde question im afraid....

Apologies in advance....

How do I do a compression test.... I have a compression guage...so im heading in the right direction i guess..
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Will
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Basically - warm the engine up, remove the fuel pump relay if you wish, disconnect the king lead from the coil. Unscrew one spark plug, screw in the compression tester gauge. Turn engine over on the starter motor with the throttle open - read the measurement on the gauge.

Repeat for the other cylinders.

Done B)
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jags2.5-16
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^ Thanks.. sounds pretty straight forward... just need an extra pair of hands...

Where's rhysmangatmotorsport's number....mmmmm
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derin100
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Will
Mon Jun 7, 2010 11:41 pm
Basically - warm the engine up, remove the fuel pump relay if you wish, disconnect the king lead from the coil. Unscrew one spark plug, screw in the compression tester gauge. Turn engine over on the starter motor with the throttle open - read the measurement on the gauge.

Repeat for the other cylinders.

Done B)
Couple of questions:

1) Where is the fuel pump relay

2) Do you take one plug out at a time? i.e leaving 3 of them in on a 4-cylinder engine and then once you've checked that cylinder replace the plug and move on to the next cylinder?

Many thanks.
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chrismatheou
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Fuel pump relay is just behind the battery and to the side of the ECU it's black and about the size of a box of fags.

You have to take out and leave out all plugs until you have completed the test.
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derin100
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Thanks Chris.
That's what I thought re the plugs. When I did that the other day with the cheapo tester I had just bought off Ebay I got NO readings on any cylinders! I reckon the tester is crap/non-functioning? You can't have zero compression on all cylinders and yet the car 'drives', huh?
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chrismatheou
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Doesn't sounds right to me the tester must be at fault. What mechanism does it have to release the pressure from the tester? Is it a button? There should also be an o-ring on the end of the thread.
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derin100
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Yeah, has a little metal button on the side to release the pressure. First time I used it registered about 70-ish psi on the cylinder that I tested...thereafter it didn't work at all on any of the cylinders.

Just been reading up on here though about head gaskets....I'm pretty convinced mine has gone? (please see my post in the Engine section)

I'm going have to get someone to look at the engine for me.
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ukhozi
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My 1987 W201 2.3-16v has a reading of 5.4 on all four cylinders and will not pull under 4,000 rpm so I guess new rings are in order but I see there are a couple of makes for this year, Gortz and Kubbelsmitt (?) is there anyway of telling or does it not matter as they are interchangable, I really don't want the engine in bits for weeks whilst I get the right ones if I can help it.
Where is the best (cheapest) place to get the gaskets and seals from in Europe?
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blankcanvas
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Johnboy Mac
Tue Mar 17, 2009 9:35 pm
Diesels 2.0 & 2.5, compression ratio 22:1, new value 26-32bar, wear limit 18bar approx.

Petrol 1.8, 2.0, 2.6 compression ratio between 9:1 & 9.2:1, new value 10-12bar, wear limit 8.5bar approx.
2.3-16 compression ratio 10.5:1, new value 14-16bar, wear limit 12.5 approx.
2.5-16 compression ratio 9.7:1, new value 12-14bar, wear limit 10.5 approx.

Note:
Diesel max. permissible differences between individual cylinders 3.0bar.
Petrol max. permissible differences between individual cylinders 1.5bar.
(1 bar = 14.5 psi)

nice one john , would expect the 3.0 to be around 2.6 figure?
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Johnboy Mac
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blankcanvas
Sun Sep 12, 2010 7:48 pm
nice one john , would expect the 3.0 to be around 2.6 figure?


No probs Dan. I'll look into the figures for a M103 3.0, suspect they'll be the same as a 2.6. I'll you know the exact figure during the week.
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