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Now that I have switched back to the 280SE for daily transport, I thought it might be due for a major tune-up. Performance is certainly 'softer' than it used to be, and fuel economy isn't that great. I recently replaced plugs, all fluids and filters, and set the valve clearances, ignition leads, cap rotor.
Now, this engine was rebuilt at an indicated 257000km (at the time it was suspected that the true mileage was 50 000 to 100 000km more). Fuel injectors were replaced at about 290 000km.
Mileage is now indicated at 437 000km, so the current timing chain has done 180 000km, and the injectors about 147 000km.
I had come to suspect that the chain must be stretched after this mileage. Today I opened up and found that when the RH cam (exhaust) is on its alignment marks, the crank damper is at about 3 deg ATDC. A lot less stretch than I imagined. I still need to do an accurate measurement based on valve lift though. I must also mention that some time ago I had to replace the water pump housing (which includes the crank timing dowel) for one off another car, so there is perhaps some uncertainty in the accuracy of the indication. So I need to probe the top of #1 to see where true TDC is.
In anycase, it seems that chain stretch is really not severe, and I can only attribute this to the fact that I have looked after the engine well since the rebuild - always on Futron semi-synthetic, changed every 7500km, most of the mileage being open-road.
I have considrered correcting the timing with offset keys, but the design of the twincam M110 means this is a VERY big job, involving releasing the camshaft from its mountings. It will me MUCH easier to change the chain than fit offset keys. However, the tensioner is a ratchetting type akin to the 6.9's one - concealed behind the A/C compressor mounting. Removal of the compressor is easy on the M110, but refitment is very unpleasant. The tensioner is completely reuseablr, but of a design that 'falls apart' when removed. THis will be the most difficult part of the job.
At present I'm in 2 minds about replacing the chain - its cheap - about $60 at the main dealer - but it looks like a LOT of work - a really full day's graft. Fuel has become so expensive there, that even if I get another 25km on a tank, it will soon pay for itself.
I have other issues - some of the tappet adjusters seem to be looser than they should be, and thus require more frequent adjustment than the manual recommends.
Its fun driving a REALLY high mileage car
Now, this engine was rebuilt at an indicated 257000km (at the time it was suspected that the true mileage was 50 000 to 100 000km more). Fuel injectors were replaced at about 290 000km.
Mileage is now indicated at 437 000km, so the current timing chain has done 180 000km, and the injectors about 147 000km.
I had come to suspect that the chain must be stretched after this mileage. Today I opened up and found that when the RH cam (exhaust) is on its alignment marks, the crank damper is at about 3 deg ATDC. A lot less stretch than I imagined. I still need to do an accurate measurement based on valve lift though. I must also mention that some time ago I had to replace the water pump housing (which includes the crank timing dowel) for one off another car, so there is perhaps some uncertainty in the accuracy of the indication. So I need to probe the top of #1 to see where true TDC is.
In anycase, it seems that chain stretch is really not severe, and I can only attribute this to the fact that I have looked after the engine well since the rebuild - always on Futron semi-synthetic, changed every 7500km, most of the mileage being open-road.
I have considrered correcting the timing with offset keys, but the design of the twincam M110 means this is a VERY big job, involving releasing the camshaft from its mountings. It will me MUCH easier to change the chain than fit offset keys. However, the tensioner is a ratchetting type akin to the 6.9's one - concealed behind the A/C compressor mounting. Removal of the compressor is easy on the M110, but refitment is very unpleasant. The tensioner is completely reuseablr, but of a design that 'falls apart' when removed. THis will be the most difficult part of the job.
At present I'm in 2 minds about replacing the chain - its cheap - about $60 at the main dealer - but it looks like a LOT of work - a really full day's graft. Fuel has become so expensive there, that even if I get another 25km on a tank, it will soon pay for itself.
I have other issues - some of the tappet adjusters seem to be looser than they should be, and thus require more frequent adjustment than the manual recommends.
Its fun driving a REALLY high mileage car
