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Discussion Starter #1
Ok, so some of you may know I was having engine problems with my 2010 Smart Fortwo http://www.smartcarofamerica.com/forums/f25/loud-knock-engine-when-shifting-48840/
The problem occurred just after the warranty ended. It was clearly knocking terribly and was likely a problem with one of the pistons. I stopped running the vehicle shortly after the knocking started and began to troubleshoot.

After talking to my local Smart dealership (3 hours away) I found they were willing to tear down the engine and if the damage was an internal defect, they would "work with me" in order to repair the motor (I just had to pay the towing fee to get it there, $800, and the teardown fee, $1500, upfront). If the problem was operator error it would cost me $10,300 to replace the engine. SOOOOO I went ahead and decided to tear it down and rebuild it myself with the help of my buddy Scott. We've taken the following steps:

1. We lifted the vehicle, dropped the engine along with the sub-frame.

2. Removed all the accessories.

3. Separated the engine and tranny.

4. Broke down the motor completely.

5. Washed all the parts in the solvent tank.

6. Found that one of the piston shims/bearings was completely worn through and was loose enough to move the piston around the crank easily when it was still put together.

It is still unclear as to what actually caused the shim to wear through or for the spacers to get loose but all seemed to be in working order. The number 1 Piston was considerably darker than the others and appeared to be somewhat burned. I have no idea what caused that to happen as it seems everything was in fairly good condition. There was some small oil build ups but nothing that a 44k mile motor wouldn't have. I do think it was a part failure. I have saved about $10K thus far and will probably save a total of $9,700 doing it myself. Thank god it was out of warranty.

I was fortunate to have stopped running the vehicle shortly after the knocking started and prevented any catastrophic failures. The parts have been cleaned and tomorrow I will order the shims/bearings and the spacers that go in the crank. I have only spent about $220 in extra tools/car cover/jackstands/fluids so far. I will continue to post pictures on the progress when the parts get here.







 

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Discussion Starter #3
You threw a rod bearing. Could have been something in the oil got sucked up and starved that bearing, causing it to fail. You should have the crank polished and the rod resized.
What could have possibly caused oil not to get to that area? I did the regular maintenance and took great care of the car. The crank and rods all look to be in perfect condition. The only parts that looks bad were the bearing, and the bottom side of the piston. We are however going to polish everything anyway.
 

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You threw a rod bearing. Could have been something in the oil got sucked up and starved that bearing, causing it to fail. You should have the crank polished and the rod resized.

+1, you definitely threw a rod bearing. I would love to see a close up of the bearing journals on the crank & the bores in the rods. You don't toast a bearing like that without journal damage. Make sure your machine shop checks the journal size & roundness. Something has to be off. Also be very careful to examine all the oil passages in the crank, the rods are fed oil from the mains, may have a plugged passage inside the crank. Also have the rods checked, and re-sized. My guess is they are out of round at this point.
 

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Discussion Starter #5
+1, you definitely threw a rod bearing. I would love to see a close up of the bearing journals on the crank & the bores in the rods. You don't toast a bearing like that without journal damage. Make sure your machine shop checks the journal size & roundness. Something has to be off. Also be very careful to examine all the oil passages in the crank, the rods are fed oil from the mains, may have a plugged passage inside the crank. Also have the rods checked, and re-sized. My guess is they are out of round at this point.
Check, I threw a rod bearing. Thanks for the advice on the oil passages, hopefully that'll give me a clue as to why that bearing was running dry. As for the rods being out of round, I am sure the #1 rod is as I could move it around while it was still attached to the crank. Like I said in the initial post, the other two were in perfect condition and I stopped running the vehicle within minutes of the first knocking sound probably preventing extreme damage. I will have those other two checked though, but am fairly confident they are still pristine.
 

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I want to offer the OP a little helpful advice here. It's pretty obvious from your post, this is your first attempt at an engine rebuild. Hopefully your buddy Scott is a good mechanic. I'm all for doing the work yourself, but be aware of what you are getting into, and don't be afraid to ask for help from a professional(NOT a smart center).

Here's a list of things I see you will need and/or need to do:

You need a full set of crank and rod bearings, do the whole set, not just the one that looks bad.

You need a full gasket set for the engine. Do not attempt to re-use any of the old O-rings or seals.

You also need to order a set of piston rings. Don't ever attempt to put the originals back in, you have disturbed the wear pattern, and they will never seal right again. While you're at it, have a good local machine shop check the bores. With only 40K on it, they should be good for just a simple hone job, but it's better safe than sorry.

While the block is there, don't forget to have the crank journals checked. I would do this before you order anything. If they aren't right, the machine shop can tell you how much undersize they need to grind it so you can get appropriate bearings.

You will probably need a set of rod bolts, main cap bolts, and head bolts. I'm pretty sure the smart uses torque-to-yield bolts, they are one use and throw away.

While you are at it, have the block & head hot tanked to make sure they are clean. When that rod bearing went, it sent metal particles throughout the engine, you need to make sure it's clean.


Take the head in as well, since you have it apart, have them check the valves and seats. Better to do it now, than get it back together and realize you have an issue.


Make sure you get all the factory torque specs for bolts. Don't guess, make sure you know what they are. I can help with that if needed.


Most important: DON'T BE AFRAID TO ASK QUESTIONS!

There are a lot of guys on this forum that are willing to help.

Good luck.:)
 

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Discussion Starter #7
I want to offer the OP a little helpful advice here. It's pretty obvious from your post, this is your first attempt at an engine rebuild. Hopefully your buddy Scott is a good mechanic. I'm all for doing the work yourself, but be aware of what you are getting into, and don't be afraid to ask for help from a professional(NOT a smart center).

Here's a list of things I see you will need and/or need to do:

You need a full set of crank and rod bearings, do the whole set, not just the one that looks bad.

You need a full gasket set for the engine. Do not attempt to re-use any of the old O-rings or seals.

You also need to order a set of piston rings. Don't ever attempt to put the originals back in, you have disturbed the wear pattern, and they will never seal right again. While you're at it, have a good local machine shop check the bores. With only 40K on it, they should be good for just a simple hone job, but it's better safe than sorry.

While the block is there, don't forget to have the crank journals checked. I would do this before you order anything. If they aren't right, the machine shop can tell you how much undersize they need to grind it so you can get appropriate bearings.

You will probably need a set of rod bolts, main cap bolts, and head bolts. I'm pretty sure the smart uses torque-to-yield bolts, they are one use and throw away.

While you are at it, have the block & head hot tanked to make sure they are clean. When that rod bearing went, it sent metal particles throughout the engine, you need to make sure it's clean.


Take the head in as well, since you have it apart, have them check the valves and seats. Better to do it now, than get it back together and realize you have an issue.


Make sure you get all the factory torque specs for bolts. Don't guess, make sure you know what they are. I can help with that if needed.


Most important: DON'T BE AFRAID TO ASK QUESTIONS!

There are a lot of guys on this forum that are willing to help.

Good luck.:)
Gentleman,
First I want to thank you for your advice, and I don't want to seem ungrateful but the reason for this thread was to give others the confidence to dive into their motor (once the warranty is up), and demonstrate that the average mechanic can get it done without the ridiculous price tag from Mercedes. With that being said, I have been turning wrenches for 15 years and 8.5 of those years for the Army. I have rebuilt much larger diesel motors, but this is the first time I have done a full rebuild on a motor this size. Fortunately, it's not complicated and the only special tools I have/will needed/need are a set of male/female torx sockets and a piston ring compressor (torque wrenches are standard in my book).

*White, I have already ordered an engine rebuild kit that appears to come with all the trimmings including the rod bolts and torque bolts.
I have already ran the parts through the solvent tank, but am going to take them to a heated parts washer in the morning.
I was able to get the torque specs from Smart of Sugarland.
Though the valve seats look great I will absolutely have them checked to make sure. Thank you.

I sincerely appreciate all the advice, please keep it coming! You can bet when I do have question, and I will, I will ask you guys. Thank you.
 

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When mechanics brought precision machined parts to my machine shop in a bucket or tossed in a box I usually sent them on down the road... :rolleyes:
Knowing how to handle and treat precision parts is key to success...:wink:
 

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Discussion Starter #9
When mechanics brought precision machined parts to my machine shop in a bucket or tossed in a box I usually sent them on down the road... :rolleyes:
Knowing how to handle and treat precision parts is key to success...:wink:
Haha, thanks for the sarcasm, Barney. I wasn't sure I'd be able to carry on without your reassurance. I'm glad people like you are here to help!
 

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Gentleman,
First I want to thank you for your advice, and I don't want to seem ungrateful but the reason for this thread was to give others the confidence to dive into their motor (once the warranty is up), and demonstrate that the average mechanic can get it done without the ridiculous price tag from Mercedes. With that being said, I have been turning wrenches for 15 years and 8.5 of those years for the Army. I have rebuilt much larger diesel motors, but this is the first time I have done a full rebuild on a motor this size. Fortunately, it's not complicated and the only special tools I have/will needed/need are a set of male/female torx sockets and a piston ring compressor (torque wrenches are standard in my book).

*White, I have already ordered an engine rebuild kit that appears to come with all the trimmings including the rod bolts and torque bolts.
I have already ran the parts through the solvent tank, but am going to take them to a heated parts washer in the morning.
I was able to get the torque specs from Smart of Sugarland.
Though the valve seats look great I will absolutely have them checked to make sure. Thank you.

I sincerely appreciate all the advice, please keep it coming! You can bet when I do have question, and I will, I will ask you guys. Thank you.


Cool, sounds like you have this under control. I didn't mean any offense with my post, just wanted to make sure you had all the facts. Been through a few engines myself, so I know the drill.

Good luck on your rebuild. I'm looking forward to see more pictures of your progress.

Can you post where you found the rebuild kit? Just curious who is offering them.

Thanks
 

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Discussion Starter #12
Cool, sounds like you have this under control. I didn't mean any offense with my post, just wanted to make sure you had all the facts. Been through a few engines myself, so I know the drill.

Good luck on your rebuild. I'm looking forward to see more pictures of your progress.

Can you post where you found the rebuild kit? Just curious who is offering them.

Thanks
White, It's all good. And again, believe me as soon as I have question I will ask...you. Haha. I don't think I can put the URL on here but Smartwsc has everything from the kit. I believe the website only has the individual parts posted but you can order everything together if you just email them. I did have to get the head bolts from smart-parts-direct though.
 

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I don't think I can put the URL on here but Smartwsc has everything from the kit. I believe the website only has the individual parts posted but you can order everything together if you just email them.
Thanks for the heads up regarding smart world sport concept (smart WSC). :D

Google is your friend - appears that they have some really cool stuff going on across the pond! After you go to their site make sure you spend some time in their gallery . . .



 

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JohnnyBravo, the point made with the parts in the bucket is that precision machined surfaces like cam journals need to be protected from damage. Doesn't have to be fancy - rags, bubble wrap, etc will do, but you need to avoid having parts knocking against each other.

I've done my share of motorcycle engines, never a car engine, but this one is pretty close in design to a motorcycle engine.

Measure the diameter of the crank journal that had the spun rod bearing using a precision micrometer (a vernier is not good enough) at several locations around the journal. If there is ANY difference between the measurements that you can measure, the journal is out of round and needs to be reworked. I am serious with the accuracy, it needs to be measured to 4 decimal places (imperial) / 3 decimal places (metric).

Crankshafts can be reworked. Known sources of crank reworking in the motorcycle business include APE, Marine Crankshaft, and Falicon. Have it repaired by welding and re-grinding. Other shops may build material up on the crank by using a plating process. I have not had good luck with local shops who do that.

Also, the con-rod on the journal that spun needs to be inspected. If there is discolouration, that is heat damage, which affects the heat treatment of the rod - it's scrap. Assemble the con-rod using the original fasteners and torque them to specs then measure the big end for tolerance and out-of-round (by measuring it at several locations). If it is stretched, a good automotive machine shop may be able to fix it by machining a bit off the rod and/or cap mating surfaces and then machining the diameter to size.

Check, check, and double check EVERYthing.
 

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Discussion Starter #15
JohnnyBravo, the point made with the parts in the bucket is that precision machined surfaces like cam journals need to be protected from damage. Doesn't have to be fancy - rags, bubble wrap, etc will do, but you need to avoid having parts knocking against each other.

I've done my share of motorcycle engines, never a car engine, but this one is pretty close in design to a motorcycle engine.

Measure the diameter of the crank journal that had the spun rod bearing using a precision micrometer (a vernier is not good enough) at several locations around the journal. If there is ANY difference between the measurements that you can measure, the journal is out of round and needs to be reworked. I am serious with the accuracy, it needs to be measured to 4 decimal places (imperial) / 3 decimal places (metric).

Crankshafts can be reworked. Known sources of crank reworking in the motorcycle business include APE, Marine Crankshaft, and Falicon. Have it repaired by welding and re-grinding. Other shops may build material up on the crank by using a plating process. I have not had good luck with local shops who do that.

Also, the con-rod on the journal that spun needs to be inspected. If there is discolouration, that is heat damage, which affects the heat treatment of the rod - it's scrap. Assemble the con-rod using the original fasteners and torque them to specs then measure the big end for tolerance and out-of-round (by measuring it at several locations). If it is stretched, a good automotive machine shop may be able to fix it by machining a bit off the rod and/or cap mating surfaces and then machining the diameter to size.

Check, check, and double check EVERYthing.
GoFaster,
Thank you for all of your advice. I got the point he was trying to make. I in fact wasn't carrying the parts around like that, I just put them in the bucket for a light cleaning with degreaser and a stiff bristle brush before I sent them to the machine shop.

My buddy who is helping me has also done many motorcycle engines and that's why I asked for his help. You're absolutely right, this motor more closely resembles a Motorcycle engine.

I just got the parts back from the machine shop today. As suspected, everything is in perfect condition with the exception of one of the bearings and a single crank spacer. I know not everyone read the entire first post, but I did stop running the motor almost as soon as I heard the knocking. I am sure I prevented quite a bit of damage as it shows.

I think it is worth mentioning after the parts washer EVERYTHING looked pristine! There was no discoloration or apparent damage.
 

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Discussion Starter #17
Excuse my ignorance, but when you are referring to the crankshaft "spacer"- do you mean the crankshaft thrust washer?
There is no excuse for your ignorance!! Haha, just messing around. Yes, the proper nomenclature is crankshaft thrust washer. My apologies for those of you following.
 

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question for all those motor gurus - in these types of failures is the conventional wisdom that the thrust bearing failed first (would result in low oil pressure but no bad noises from the motor) then the rod bearing went secondarily?
 

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question for all those motor gurus - in these types of failures is the conventional wisdom that the thrust bearing failed first (would result in low oil pressure but no bad noises from the motor) then the rod bearing went secondarily?
Not in my experience, but I am no guru. I have seen a number of engines in the last few years with isolated rod bearing failures. I guess they don't make them like they used to. Also, when a rod bearing starts shedding metal particles they can circulate with the oil and act like an abrasive on moving parts. The thrust bearing has a significant load on it when the clutch is disengaged, such as when idling in gear at a stop or shifting.
 

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Anything that can cause low oil pressure or low oil supply rate can lead to a con-rod bearing failure. I hate putting an engine back together that has had a failure like this, without knowing WHY it failed.

- Improper oil clearance in the bearing from the factory. Rare, but it happens. Check dimensions and oil clearance against specifications.

- Clogged oil filter due to neglected maintenance or installation of an incorrect oil filter for the engine.

- Grossly incorrect engine oil viscosity or grossly neglected oil change interval.

- Oil consumption for other reasons (rings, valve seals) leading to low oil level undetected by the driver (never checking the dipstick) leading to the oil pump sucking air.

- Failed (stuck open) oil pressure relief valve. Make sure the relief valve is properly sealing shut and the spring pressure is in the ballpark of what it should be.

- Worn oil pump gears or housing. Inspect. Only likely on a hi-miler or if oil changes have been neglected.

- Cooling system failure leading to high oil temperature (i.e. low viscosity).

- General wear inside the engine, particularly on the main and rod bearings, leading to oil demand beyond what the oil pump can deliver (low oil pressure). Only likely on a very high mileage engine or one in which oil changes have been neglected.

- Lugging the engine at low revs and high torque demand - particularly if fuel of insufficient octane is used, leading to detonation which causes high cylinder pressure - that pressure gets transmitted through the rod bearings. Small-displacement high compression engines generally would rather be spinning moderately fast instead of being lugged down under load. With a car having an automatic/automated transmission, excessive lugging is prevented by the automatic downshifts.

- On the other hand, excessive over-revving can result in a demand for oil to feed the bearings that is beyond what the oil pump can deliver. But ... that's what rev limiters are for. Normally, any production vehicle is designed so that anything below redline on the tachometer is fair game.

- Engine oil of too high viscosity, or revving a cold engine hard (same effect), can cause a situation similar to the above ... the oil won't flow fast enough when it's too thick, either due to inappropriate viscosity or because it's too cold. Take it easy on a cold engine.
 
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