I finally got around to doing a compression test on my '83 300SD.... 400k miles. We were in upstate NY where the weather consistently was in the teens and single digits, some days below zero.... I was having a tough time starting it easily in the cold once it hit to the teens and so I did a valve adjustment.

After the valve adjustment, I didn't notice much improvement. When I got the car 2 1/2 years ago, it purred. Lately I've been noticing an unstable idle when just starting, I'm guessing the rack damper bolt needs replacement.

A year and a half ago, I changed the timing belt tensioner gasket as it was gushing oil out the side (I also did the crankshaft seal, just in case).... after that, it seemed to ride a bit rough. I was thinking maybe the tensioner spring is worth replacing, if it wears down?

Lately in the last few weeks I've noticed that I MUST keep my foot on the pedal during the first 10 minutes of starting (even if it's 50-60 degrees outside), otherwise it idles really rough and risks stalling. I've been doing this trick backing out of my driveway where I keep my foot on the gas while I switch from reverse to forward gear.

Would the rack damper bolt potentially resolve the rough idle? I've looked online and see that there's supposed to be an o-ring that goes at the end (that may need replacement), and I've had a tough time finding sources for that....

What effect would getting a new timing tensioner spring help? What situation would I notice that would warrant replacement?

So I finally got the compression test done today, and once I got it back together, the car seemed to purr more and shake less. I'm not sure if it was because the engine was warm (seemed better than normal), or if I had tightened something that was loose prior (a loose injector?). I will find out in a few days on a cold start how it fares.

The compression test made me a bit concerned because cylinder #4 was about 25% lower than the highest cylinder (#1). The results:

#1: 380 psi
#2: 380 psi
#3: 320 psi (16%)
#4: 290 psi (24%)
#5: 340 psi (11%)

I've read that anything above 275 is "fair", and that the compression isn't awful, just that the difference is more problematic. What happens when the compression varies so much, even if the lowest is still acceptable? Is it just a higher chance of rough idle? Cold starting troubles?

Is there anything that can be done with the one "bad" cylinder that isn't major overhaul? While keeping the engine in the chassis? Is a lift required, such as if the head gasket needed to be replaced (I have the FSM)? Or is it something to do with the piston/cylinder?

I'm potentially selling the car within the next few months and I was curious how the compression might affect the value/sale price. The mileage is supposedly 400k, so maybe that's par for the course? Any ideas how much life I might have left in the engine? I JUST did a valve adjustment, but given that it's just a SINGLE cylinder that's way out of range, I will give it another go with checking the valves.

I imagine that how well it starts in the cold is a good indication.... The biggest issue in the single digit weather was the rough idle/potential stalling until the engine warmed up.... But then again the rough idle was apparent even in warmer weather. I was worried it was the compression, but from these numbers, my guess is that it's elsewhere, maybe the rack damper bolt or the idle adjustment. My tach is broken so I can't accurately adjust the idle except by ear.

If you're certain of the valve adjustment, the next step would be a leakdown test. The low compression could be a valve, valve seat, or guide. That would be easier to deal with than rings.

If you can get the Car to run OK no one is likely to want to check the Compression.

However, if the compression variance is correct it can cause an uneven idle.

When I had hot idle shaking on My own Engine the new Governor Idle/Rack Dampner Pin (buying and insall a New Rack Dampener Pin was the first thing I tried) did not help till I did a Valve Adjustment, rebuilt the Injectors, changed Transmssion and Motor Mounts.

After that was done the new Governor Idle/Rack Dampner Pin was able to remove a little more shake.

If the compression loss is due to sticking Piston Rings changing to synthetic Oil and driving a few 100 miles has been know to free them up.
Or you can try pouring some Marvel Mystrey Oil in the Cylinder and letting it soak for a week or more do disolve the Carbon.
There should be some info on soaking the Cylinders, Rings and Pistons in the DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/
http://www.peachparts.com/Wikka/DoItYourSelf

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84 300D, 82 Volvo 244Gl Diesel

The best cure for the idle shakes I've found was several valve adjustments in a row with about 100-200 miles in between.

I've also noticed, according to the FSM, engine temperature during the adjustment has a fairly significant effect on tolerances. If you are doing the valve adjustment during cold weather, this may be a factor as well.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I will try another valve adjustment and see how that goes.

This may sound stupid, but is there a way I can LOWER the compression in the other cylinders (maybe by overcomensating on the intake valve clearance), so they are at least close enough to each other? In hopes of reducing the idle shaking. The lowest cylinder's compression is 290 psi, which I understand is still decent, especially for 400k mi.

I know I definitely need to replace the rack damper bolt (the idle ping pongs). However, the shaking is less an issue as is the engine simply stalling when cold. If it easily stalls (I have to push SLIGHTLY on the pedal and it won't stall after that, plus the idle smooths out), would that infer the rack damper bolt (ie an injection issue) more than the compression? I would think that the other 4 cylinders wouldn't lose adequate pressure to stall out, regardless of the issues with a different cylinder. To me it just seems like an issue with idle regulation at the IP.

If you want uniform compression that low, you will have no problems whatsoever as long as you move to texas or arizona. Alternatives would be starting it only between May and October.

Leakdown test will tell you where the leakage is on the low cylinder. Can lend leakdown tester if you require.
MMO soak is a $5 fix you can attempt on the low piston, this is the only fix for ring leakage I know of before rings, liners & the rest.
I'd check the fully open cam clearance to the valves on the low cylinder. No reason to put a wrench on it if the clearance is correct.

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CC: NSA

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Time for rebuilt injectors?

If your injectors are worn, and the opening pressures are off (relative to the other injectors) by more than 5 bar, engine will have increased idle vibration/shaking.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

yeah the injectors definitely are worn, 4 of the 5 are fairly concave on the end of the injector... I'm at a point where I'm going to be just selling the car so I honestly don't know if it's worth the $100 to get new injectors (I have the monark nozzles) balanced/tested. Especially if it might not do anything.

I have an idle rack damper bolt and a new timing tensioner spring on order and will see what those end up doing.

I checked the valves again and the #4 in question was a bit off compared to the others. When I start it cold and let off the pedal, it seems to run more smoothly than before, but it still aims to stall out at first.

Would rebuilt injectors (costing me $100 to balance/test) honestly raise the value of the vehicle (when selling)? Or should I just give the new owner the nozzles and have him deal with it? Something I need to consider after I've replaced the rack damper bolt and tensioner spring.

If I were to just simply replace the nozzles with the existing injector internals (trying to not mix them up), would the pressure/spray pattern/quality be any worse off than it already is? Obviously that may be a factor to the idle/shaking, but maybe I can take the chance and see if anything improves at idle (without necessarily testing/adjusting the injectors). Just trying to see if I can get things in "good enough" shape to sell.

A doubt a rack damper bolt will help. If you get serious shaking AFTER THE ENGINE IS AT OPERATING TEMPERATURE, then the RD bolt is suspect.

No way to know if you should invest in injectors, if you do and the problem is cured, still want to sell it?

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83 SD

84 CD

I drove an SD with similar compression numbers through a winter. As compression decreases, you have to address the other parameters of starting to compensate. So... you can continue to drive the car in winter if:
- the glowplugs are NEW Bosch at least every two years, preferably every year
- the starter is turning fast enough
- you have a reasonably fresh battery
- you have a block heater installed
- you adjust the valves every fall
- you run either PowerService diesel additive (white bottle) to raise the cetane level for starting, or add kersone to your diesel in the coldest months
- preferably, you install a manual glow control setup that allows you to easily vary the glow cycle according to the temperature (yes you can do multiple cycles with the existing controller, but I find this approach more convenient).

This winter was exceptionally bad. The conditions we saw for two months or more, steady, usually only happen for a week or two. The sustained temperatures represented a torture test for any older diesel.

If every winter was like this... I would not be messing with old diesels. Period.

If your rough idle is only when cold, the rack damper bolt will not do anything about it. The loping idle that signifies the old style bolt isn't sufficient occurs when the motor is hot.

If the car wants to stall during warmup, you need to raise your idle speed for the winter months. I had to adjust mine with each season, on that old SD. You could also consider looking for one of the 'postglow' relays that were sold aftermarket by Bosch for a while. These stay on for an extended period after the glow light goes off (2 minutes if I recall correctly). That makes a significant difference to how the car runs in cold weather after startup.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

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