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Discussion Starter #1
After a whole bunch of research on why my Smart was hard to start and was idling rough it turned out to be worn valve guides. I did the work myself and I just thought I would share the pictures. I am a motorcycle/atv machanic and have a small shop on my property so it wasn't much different working on the little Smart.

Symptoms before tear down:
Hard to start. Even worse when warm.
Rough idle
No smoke
Spark plugs normal
No codes or check engine light.
Variable numbers on the compression check.

Diagnosis:
Extremely warn valve guides. All of the exhaust side and most of the intake side. This was causing the valves to seat randomly causing the variable compression numbers.

The fix:
Mercedes/Smart does not sell the valve guides alone. They sell the whole head($1299.00). I went to my local machine shop and had my old guides along with a new valve put in the cnc guidance machine and had a cnc program made. They basically replicated what a new guide would be. Then I had new guides machined. I did spend some real money to have this done but, now I own the program for the cnc machine and I sell sets on eBay for a very low cost. I am not going to get rich. I would like for maybe a break even in the end.
I replaced all my valve guides and 4 of the valves. Went ahead and replaced my timing chain and tensioner. That was it besides the gaskets, seals, and spark plugs.

The car had 48,000 miles on it so, I was a little surprised by this major mechanical failure. I have 8000 miles on the new head and it runs great. I did go ahead and port and polish the head while it was apart.

Enjoy the pictures.

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I've seen your guides on Ebay and even posted them on a thread here somewhere. Might take a while to make your money back, but as more smart engines get higher mileage on them, more people will start rebuilding the heads instead of the dealer throwing a very expensive new head at it. Did you have any issues with adjusting the new valves? Did you buy any new bucket shims?
 

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That's quite an interesting position for the drivetrain ...

Looks to me like you've removed the control arms, disconnected the rear shocks, and disconnected the right-side engine mount, and just let the whole deal hang down.
 

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Discussion Starter #5
I actually removed both upper engine mounts and left the front one connected. I was able to leave a few things hooked up. Worked out great. I have a hoist in my shop so I was able to lift the rear of the car high in the air
 

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I'm having the same issues, I bought mine with a blown head gasket though. The valve guides are absolutely worn out and the engine has only done 50,000 miles. It's shocking really, just poor design.

Could you tell me which way the guides come out? I'd be very interested to see your drawing of them too if that's possible. I'm considering making mine from ampco 45 and possibly putting a few small notches in the stem seals since they clearly aren't getting enough lubrication.

Looking at whatever data I can find about other engines on the internet, the clearance on the inlets ought to be between 1-1/2thou and 2thou on the inlet and perhaps 2thou to 2-1/2thou on the exhaust?

It would be great if you could share some of these details, there's nothing in the internet anywhere about these engines that I can find.

I also can't find the tappet clearance information anywhere, can you tell me what those should be?

Cheers,
Roger
 

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Discussion Starter #7
I have some pages and specs from a service manual I was able to "borrow" but, they are out at my shop. The guides press out from the piston side up like most. I will see if this my phone will let me upload a picture of the guides. I just listed another full set of guides on ebay. I sell them cheaper than you can get them made. The ones listed now are carbon steel. I have some silicon bronze ones that will be cut. I am waiting on stock material that has been backordered for a couple of months already.
 

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Dracha's engine finally wore out at 175,000 miles.... burnt valves. Instead of just putting in a new engine we opted to have it rebuilt... I'll never make that mistake again. Finding the valve guides.... then actually getting them fitted... total process took close to 3 months. It was also more expensive than just putting in a used engine.
 

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I have some pages and specs from a service manual I was able to "borrow" but, they are out at my shop. The guides press out from the piston side up like most. I will see if this my phone will let me upload a picture of the guides. I just listed another full set of guides on ebay. I sell them cheaper than you can get them made. The ones listed now are carbon steel. I have some silicon bronze ones that will be cut. I am waiting on stock material that has been backordered for a couple of months already.
I'd be most grateful for anything you have in terms of technical data, and more pictures would be great. At least I know which way they come out now.

I have a machine shop so I was planning on making the guides myself. The key information is the clearance though, it would be good to know what you used. I can guess from the information I've found, by to have if from Smart Technical data would be great.
 

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Dracha's engine finally wore out at 175,000 miles.... burnt valves. Instead of just putting in a new engine we opted to have it rebuilt... I'll never make that mistake again. Finding the valve guides.... then actually getting them fitted... total process took close to 3 months. It was also more expensive than just putting in a used engine.
I think it's only viable if you can undertake most of the work yourself. I'm lucky in that I have that facilities to do it and there's no rush. I bought it as a project to finally replace my ageing 450 which has 105,000miles on it.
 

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I have a question regarding the 'new' carbon steel guides. Customarily, aren't the guiides usually a softer material (i.e. bronze/brass) to reduce valve stem wear? I know the valves are easier to replace, but I'm wondering if the valves are that much easier to obtain, or inexpensive enough to have this make sense.
 

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I've just been in touch with AMPCO at AMPCO METAL - ampcometal.com - COMMITTED TO INNOVATIVE PRODUCTS AND CUSTOMER SERVICE FOR ALMOST 100 YEARS and they say that AMPCO®45 is the best suitable alloy for valve guides.
Ok, you might say they would say that, but looking at the various offerings of guides on ebay, it does seem to be a popular choice. I'm really surprised to hear that any guides are being made of Steel, I've never heard of that before.

Stop Press.... I've just pushed out the first of the valve guides and guess what..... yep, made from steel. So there's your answer, it's a hopeless material to make guides from, the amount of wear is astonishing for an engine with only 50,000 miles on it.
 

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Preliminary drawing

For your information only, I've measured the valve guide and valve to the best of my ability (micrometer for the diameters) and have created what I believe to be an accurate representation of it.
I've estimated what clearance I think should be necessary for both inlet and exhaust, based upon information found on the internet for similar sized motorcycle engines.
Use this information entirely at your own risk, I'm not suggesting that you make these to my drawings or that they will work if you do.

http://s1017.photobucket.com/user/rogerfroud/media/Smart%20451/Valveguidepreliminarydrawing_zpsce0544f2.jpg.html?filters[user]=138881657&filters[recent]=1&sort=1&o=0
 

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When I hear of many cars getting well over 100,000 miles with no problems, I've got to think that a bad engine at only 50,000 miles had to be helped along quite a bit by poor or no maintenance. Did you have any kind of a maintenance history on your car?

Len
 

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Seriously doubt that the guides are made of steel... Think you'll find they are cast iron or powdered metal based... The silicon content makes for a good deterrent against galling...
 

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It's possible it may be a powdered material but it's highly magnetic and can be marked with a file. It certainly has the look and feel of steel.
I don't have any history, it was just a cheap ebay purchase I bought as a bit of a gamble. There was a lot of sludge in the sump so I don't think it's been that well maintained.
The cylinder bores look fine and there's no obvious wear at the top end so it's not been starved of oil.
My guess is the wear is due to a combination of things... Poor choice of materials, too effective stem seals and not changing the oil frequently enough/wrong grade.
It's not the first car I've heard of with this problem though so there's clearly a design element in there.
 
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