Big End Bearing Replacement SLK 320

[dave100]

I'm considering replacing the big end and main bearings on my SLK320. I'm well aware that it would be better to do a full engine out bottom end rebuild with reground crank, new oil pump etc but I'm on a budget and the rest of the car isn't that special to warrant the cost, it also has 135k on the clock which keeps the value low. I just want to get a few more years out of it as a daily driver so intend a reshelling job in situ before it gets too bad and hope it hasn't damaged the crank surfaces yet.

A few queries:
Dropping the crossmember or raising the engine will be needed. Any suggestions which is easiest? I'm leaning towards dropping the crossmember. I have a hoist to hold the engine up.
Any special tools other than a torque wrench and sockets needed? I take it the big end bolts aren't stretch bolts or anything silly?
Any other parts needed other than sump gasket and the bearings which I already have?
Is there anything I'm likely to have difficulty getting apart (steering column? Engine mounts?)

Any advice much appreciated.

Thanks
Dave

I'm 90% sure it's big end knock but will get an expert opinion and oil pressure check before doing the job just in case it's something else but from previous experience that's what it sounds like to me.

 

[Wayne.clk]

Personally I wouldn't bother if it's knocking the damage has been done,
how do u intend getting the shells out without removing the crankshaft? Not that easy!
Doing a half job is pointless if u ask me

 

[ernie]

Back in the day, we were always taught that you only replaced shells if you wanted to get rid quick and that was only if they couldn't be quietened by other means!

ERnie

 

[toolman1954]

Hi,
I have tried this in the past, putting big end and mains on a Triumph 2.5. It ended in tears and in the end I bought a used, good engine, and a weekends work and it was running sweet as a nut.
I see there is a low mileage, M112 engine on Ebay at the moment, but perhaps you could source a cheaper one.
Add up all your costs for bearings. gaskets etc and the time you are going to be laying underneath, with oil dripping onto you, shi*t in your eyes and you gash your knuckles trying to fiddle in the shells. Deduct this from a weekends work and a replacement engine. You can dismantle your old engine and sell parts on Ebay to recoup some more costs.
Just replacing the engine is really a no brainer.
As Wayne has said, damage will now have been done, it will never be right. You will always be wondering if it is going to go bang big time. Also you might get many many more years out it with another lump in it.

Steve

 

[dozypillock]

If it is like mine, it only sounds like big end knock on start up for couple of seconds?
If so, mine was diagnosed as engine mounts, which is a common problem.

Neil

 

[dave100]

Thanks for replies folks. I have successfully reshelled other cars in the past and it is possible that the crank can escape damage in the early stages (and it's not that bad yet), though of course unknown until strip down. Shells usually come out pretty easily, just take the cap off and the upper one generally slides out.

The way I see it: If the sump was easily accessible I'd have no qualms but of course it isn't. Cost wise, the bearings were £80 for both big ends and mains from euro car parts. If I can get it done in a day that's a lot less cost and work than a replacement engine (again an unknown quantity), If it still fails after a while I haven't lost a lot.

Ruling out engine mountings as the knock for a few seconds from startup wouldn't go away (it comes back on hot engine and yes I have fresh mobil 1 and correct filter).

I can't seem to get an oil pressure reading on Torque from the OBD port so guess I would need to connect a gauge somewhere (take off point near oil filter?).

Don't know that I'd bother replacing the engine on a car with a value of around £1.5k. Just buy another whole car. I bought it over a year ago with rough (original) paint with FSH for £1.1k and some surface rust. I ground the rust out and had it vinyl wrapped in gloss red to same shade as Merc Magma red for a further £1.1k so whilst it looks good (nobody has yet noticed it's a wrap until pointed out) I'm under no illusions that it has much value. The parts are probably worth more than the whole car.
Dave