Questions about chain guide rail, upper and lower

[fj0-]

I've seen it being called different here and there, chain guide rail, or chain tensioner or...

I'll show a photo of what I mean, look at number #14 and #17:





Here is the upper rail, the smaller of the two, that was in my engine:




Not a pretty sight is it? I understand that one has to be replaced! Are there any aftermarket ones? I believe I saw someone post a link to a website in germany/netherlands that sold them?

Now the question I have is, the lower one, how do I know if it needs to be replaced or not? It's hard to see it all the way down but it is not even close to as bad as the smaller top one above. You can see marks but they arnt that bad. What do you think? Sorry for the bad picture:




I'm trying to figure out if I can mount my cylinder head and then mount the upper one when I get it in 3 days or so. Or if I have to replace the lower one as well, then I cant mount the head before I replace that one.

Thanks in advance, appreciate your help!

[fj0-]

Maybe I didnt say but I have researched this subject on the forums and the info I can find is that most people replace the rails just to be safe. And I would love to be able to do that without even thinking.

I really wanna get the car running. I've had it for 10months and I have barely driven it at all, maybe for half a month when I bought it. There has been problems after problems. But I DONT want to put all this effort that I have to go out and save 500$ and then have the engine fail on me after a month! But still, I need your opinions.

I looked a little closer on the lower rail and got some oil off of it, also got some better pics. Looks worse now but still not even close to the upper one, what do you think?

EDIT:
I just wanna add that I tried feeling how hard the plastic was with my fingernail. On the upper one its rockhard, and the lower one will show a little mark from my fingernail for a second or so. But I have no idea how hard it should be when new for example. Just wanted to say that, if it makes any difference.

[Jake]

You should replace it. It's worn, hard, and you have the head off. I can't think of a better time to do it.

Jake

[t13vom]

I second Jake... It is pretty impossible to do with the head on the car... Considering the cost of a rebuild replacing the rails is cheap insurance.

[Ironhead]

You should replace it. It's worn, hard, and you have the head off. I can't think of a better time to do it.

Jake

I agree, it should be replaced...

Having said that, the material hardens very quickly. I had my head off with maybe 20K miles on the rails, and they were already very hard. No longer rubbery at all.

[///schwartzman]

I've seen worse, but like Jake said, with the head off there is no better time to change them... 1/2 of the job is done. What are your plans for the future? If it includes removing the head, front cover etc. within 20,000 miles... you may be able to get away with it, but would you really want to risk it?

[Dominic]

Guys, what is the failure mode if the timing chain rails are allowed to get worn too much? If Mario was to leave these parts in the car and they continued to wear, what are the possible repercussions?

[fj0-]

I much like you understand that replacing it now instead of opening up the engine just to replace it later down the road would be alot smarter! I am doing the labour alone together with some friends so I'm not charged labour costs, even if my own freetime costs as well, of course, in some way or another.

But you have to draw a line somewhere, or else I can pull the engine and replace everything in it, including the block, and head, and... Well you guys understand my point. I have spoken to several mechanics and they think its ok to use the lower one, but not the smaller top one.

Thing is, if I remove the engine front cover to replace the lower guide rail, then I can go ahead and replace the chain, and the white rail at the intake side of the engine, and....

I am also wondering what Dominic just asked about what are the most likely repercussions if the lower rail gets worn out in say 1000miles after I put everything together?

Will there just be a noise? Will the whole engine need a rebuild? Or is "all I need", is to open it up and replace the lower rail? Because that is alot of work for just replacing that rail.

Can you replace the lower rail without removing the cylinder head?

I talked with my dealership, the largest dealership in the capital of Sweden. He could look 2 years back in their order history and he said that he had 6 of the upper rail in Sweden, so he could have that to me for tomorrow. And they have sold alot of those. They have only sold 2 of the lower rails in 2 years. He could order it for me from Germany but it would take a week to get it. This doesnt say much more than that they sell more of the upper than lower. But I kind of think that it shows that the upper rail is the one that shows most sign of wear?

[Jake]

I've not heard of one failure attributed to a worn lower tensioner rail.

Jake

[///schwartzman]

I've not heard of one failure attributed to a worn lower tensioner rail.

Jake

+1, it will continue to wear in the same pattern, you'll likely hear increased chain noise but in my observations of 4 used ones I picked up during my rebuild is the rubber seems to harden then disintegrate into very small particulates. It does not clog the oil pump or disrupt operation of the motor, by design I imagine. I would say they are good for over 200k miles (street driven, less for track cars for obvious reasons).

You should be fine if you change the upper & don't mind the labor reuse the lower, it looks good for at least another 20k, check it then and keep an eye in your oil pan.

[inastrangeland]

The biggest issue would be if it wears down to the metal. Based on how many miles are on the motor and the amount of rubber left, you get some idea of the wear rate and how many miles before you need to replace it. I have a motor with >190K miles on it and I expect to replace pretty much everything when I rebuild it.

[Dominic]

The biggest issue would be if it wears down to the metal. Based on how many miles are on the motor and the amount of rubber left, you get some idea of the wear rate and how many miles before you need to replace it. I have a motor with >190K miles on it and I expect to replace pretty much everything when I rebuild it.

Ok, so the real issue with the chain rails is that they could wear all the way down to metal underneath the rubber, and then the metal chips would cause accelerated wear in the rest of the engine. Thanks guys!

[M3 Adjuster]

I would leave the lower one alone personally..