Funny warm start noise.. - PeachParts Mercedes-Benz Forum

wolf_walker · #1 12-10-2008, 10:38 AM

117K 73' M110. Valves were quite tight when I got it, adjusted, checked and adjusted a few days later, this was a couple weeks of driving ago.
I've noticed now, on warm re-start only, more so after sitting for awhile, about 2 seconds after the motor catches there will be a pretty good clack clack clack for about three beats and then it returns to normal M110 clatteryness. I'm assuming it's taking a moment for the hot oil that has drained off to return to somewhere in the head? Pressure is fine on the gauge. I figured I'd check and make sure one valve isn't loose again or something, all the adjusters were quite stiff turning. Oil is Rotella 15w40, filter is OE.

Pooka · #2 12-11-2008, 12:19 AM

Sounds like your timing chain is slapping. A worn hydraulic actuator could do this.

These are easy to rebuild, so you might want to just rebuild this and see if corrects the problem.

Pooka

wolf_walker · #3 12-11-2008, 09:43 AM

That would make sense, the way the sound is.
Are they externaly accesable?

Pooka · #4 12-11-2008, 02:21 PM

They normally are, but only a good manual could tell. They are usually on the right hand side of the engine and mounted on the block and not the head. The correct name for this is the hydraulic chain tensioner.

Look for a hydraulic cylinder looking thing with one small oil line going to it. They are normally held to the block with two allen head bolts.

Check a manual first, but on a lot of the older cars you remove the oil line, the two allen bolts and pull it from the engine. You then take it apart and rebuild the seals inside of it.

If you have ever seen a slave cylinder on a hydraulic clutch actuator then you know what it looks like.

Check a manual first, but it is normally a pretty easy job.

Pooka

wolf_walker · #5 12-11-2008, 05:04 PM

The chain tensioner I see listed for sale comes as a sleve of sorts, a long thin spring and a cap with an allen wrench opening. Is it strictly oil pressure fed or spring force too?

wolf_walker · #6 12-11-2008, 07:15 PM

After some reading, it does not seem that the M110 tensioner is oil pressure fed, but rather a mechanical ratcheting part, hence the spring. Are they still prone to sticking or some sort of failure? I plan to check chain stretch this weekend, but as clean as the top end was I don't expect it to be excessive. That clack clack clack on warm start is surely worrisome, but I'd rather not throw money at things till I know what it is.

I mentioned the valves were all quite tight, can cam lobe or rocker wear cause a momentary clacking? I can't quite see how off hand.

79Mercy · #7 12-11-2008, 08:40 PM

when you start the motor, does the oil pressure rise very fast or does it delay. After the oil pressure comes up does the clacking go away?

This has nothing to do with your problem, but does the motor have any oil leaks, just wondering?

wolf_walker · #8 12-11-2008, 10:39 PM

Quote:

Originally Posted by 79Mercy

when you start the motor, does the oil pressure rise very fast or does it delay. After the oil pressure comes up does the clacking go away?

This has nothing to do with your problem, but does the motor have any oil leaks, just wondering?

Pressure on the dash gauge does what I consider normal for a Mercedes. Comes up to full quickly on cold start and stays there till it warms up, gradually comes down as it warms at idle, but still jumps to pegged full with much RPM. The clacking is likely about the same time the oil pressure comes up on the gauge when warm, but we're talking about from turn of key to clacking done a span of time of maybe 4 seconds at the outside. It's very brief.

There are some weeping leaks on the front of the motor, looks mostly on the drivers side starts about half way down the cam box, may have been valve cover in the past but not now. It's not enough to drip, and not real bad for it's age.

Also possibly worth noting, this is a carbed car and warm starts the rpm's tend to jump up a hair for a moment, maybe 1500rpm or so.

Pooka · #9 12-13-2008, 10:08 AM

I checked out the photo of the tensinor on Fastlane parts and you are right. I notice they sell the srping sepertarly. Could it be that only the spring needs replacing?

Also the carb part is important. It could be that it is too rich on start up, but I am not familiarr with that carb enough to know if it has an enrichment cycle on start up.

I can duplicate the sound on any carbed engine by blowing in a generious amout of starter spray before starting. The clacking there is preignition of the hyper rich solution in the cylinders. It goes away with-in about one second.

This would be a much harder problem to correct than replacing a chain tensineor.

Anyone else have any thoughts on this?

Pooka

wolf_walker · #10 12-13-2008, 12:55 PM

It's possible it's the carb, I've had plenty of issue with the solex, though I think it's more lean than anything else. The sound does not strike me as preignition, but it's hard to tell for sure.