ENGINE REBUILDERS PTY LTD
7 BARRETT STREET, FLEMINGTON VIC 3031,
TEL: (03) 9372 3111, FAX: (03) 9372 3122
ACN: 006 798 492 ABN: 74 006 798 492
TECHNICAL NEWSLETTER
Subject: Mercedes engine 111 used in models 124 , 163, 170, 202, 208, 210.
Broken camshaft 2000 kms after head work.
December 2005
Problem:
This head is a 16 valve twin camshaft design driven by a duplex timing chain and a TWO stage chain tensioner. The head came to us after breaking a timing chain. We did not see the chain and received no explanation as to why such a heavy duty chain would break. The inspection found four exhaust valves and two inlet valves bent. The head was reconditioned and an after market timing chain, tensioner and rails supplied. At that time we could only assist the installing mechanic with a diagram of the chain layout. No other specs were accessible to us.
Two weeks later, we received an enquiry from another local mechanical shop about a broken exhaust camshaft in what turned out to be the same vehicle. The break was at the drilling some 20mm back from the sprocket and mid point in the front journal. It had travelled 2000 kms and the owner had refused to have the vehicle taken back to the original repairer.????
The inspection at the vehicle was limited to what could be seen with the rocker cover removed and the broken camshaft on the bench. The chain was still intact and appeared not to have slipped it’s timing on the front (intake) camshaft. All eight exhaust hydraulic lifters (bucket type) were at the same heights and the mechanic was going to proceed on the assumption that all valves had survived.
The camshaft break was examined with a 10 power eye glass and no sign of a crack was evident. A pre existing flaw, such as a crack from the earlier chain failure, will generally be evident from a darker section at the edge of the new break. This was a single incident break.
The owner authorised two new genuine camshafts at $2900.00 plus labour.
Meantime our network found the installation procedure to help this mechanic.
Cause and the Cure:
Following up the next morning, the mechanic’s report was that this chain tensioner design was very difficult to set when the chain has been disturbed. It is all the more difficult working in the space available with a close fit of the engine against the fire wall. (East west mounted). The tensioner access is from the fire wall side of the timing case. However, with improvised tooling, the mechanic followed the procedure and felt sure that the previous mechanic had not set the tensioner correctly and had over loaded the chain leading to the broken camshaft.
The second mechanic reported only 100 lbs compression all round after fitting the cams…….He is hoping that this is a lifter problem. We will find out later.
We will be crack testing these cams in future; just to be sure.