M117 guide rails: Replacing aluminum-backed style w/plastic - PeachParts Mercedes-Benz Forum

Tomguy · #1 11-01-2004, 02:53 PM

I have the aluminum-backed guide rails - I assume they are original
I want to put the plastic ones in - at least for the time being - to see if it helps my stretch indicated.

The top retainer bolt seems fine - fits in there well - but the bottom one seems way too loose! The hole on the guide rail is an oval shape, not perfectly round - looks like the Bristol racetrack or something.

Is this right? Wrong? I have other bolts from an engine that had (other) plastic rails in it - the rails seemed snug in that head, but they dont fit in this rail either, the only difference from mine is that they dont have the groove for the spring-wire to center the old-style rail.

psfred · #2 11-01-2004, 08:37 PM

Rails have absolutely no effect on "stretch" because they do not touch the chain on the "tight" side. Only the tensioner rail touches the chain except to control vibration.

I would only replace them with plastic if badly worn, the aluminum ones don't break in service like the plastic ones.

If you have excessive chains stretch, you must replace the chain (about $90, cheaper than new rails!).

Peter

joshhol · #3 11-01-2004, 10:12 PM

Quote:

(about $90, cheaper than new rails!).

Hmm, do you mean replacement aluminum backed rails? Are they available?
Plastic guide rails were 6 or 7 bucks if I recall. The new tension rails are aluminum backed.

psfred · #4 11-02-2004, 12:28 AM

Aluminum backed rails were phased out in the early 70s. Much more expensive than the plastic ones, I think, and no longer available except in junk yards.

If the chain is stretched, it's gotta go....

Peter

Tomguy · #5 11-02-2004, 02:39 AM

Quote:

Originally Posted by psfred

Rails have absolutely no effect on "stretch" because they do not touch the chain on the "tight" side.

Well, I dont think that's right - for example, the rail opposite the tensioner on the passenger/right side head does ride against the tight side of the chain (although my aluminum-backed one does not have much visible wear on this rail, I am thinking maybe the wear isnt visible due to uniform wear?)

I see where it says "Larger pin may be required" - would I just need 1 for each, for the bottoms, or should I get them for the tops too? Probably wont though, because then I'd have to drill larger holes in the head to put larger diameter pins in.

Remember, the tensioner is on the slack side - that's why the right cam typically indicates more stretch, the chain goes from the crank to the left cam, then the dizzy, then the right cam, if memory serves (It might hit the dizzy at another spot though). If there is x amount of chain between the crank and left cam, and y amount of chain between the left and right cams, the right will be y's strech length degrees later than the left, and x+y later than the crank.

Timing chain is cheap I suppose, cause it'd give me much better mileage (am thinking 5MPG is not out of the question), giving me much more out of a tank of gas. Oh yeah, another reason I won't vote for Bush... if he's in for another 4 years I won't be able to drive my 4.5, I can't afford paying $4 a gal for gas

WANT '71 280SEL · #6 11-02-2004, 08:42 AM

Wasn't it Kerry that supported the $.50 gas tax increase? And he doesn't own any SUV's? Just his family owns the 5 or so Suburbans? LOL, give me a break. I guess Kerry just knows how to use his SUV's responsibly, the rest of us all are just stupid and incompetent.
Thanks
David

Tomguy · #7 11-02-2004, 10:33 AM

Quote:

Originally Posted by WANT '71 280SEL

Wasn't it Kerry that supported the $.50 gas tax increase? And he doesn't own any SUV's? Just his family owns the 5 or so Suburbans? LOL, give me a break. I guess Kerry just knows how to use his SUV's responsibly, the rest of us all are just stupid and incompetent.
Thanks
David

Kerry isn't the one who recieves "donations" from the oil companies, nor is he the one who refuses to release the strategic reserves to correct the gas prices

And no, he didn't support the $0.50 gas tax increase, just like Bush wasnt personally responsible for 9/11. I don't believe attack ads for either party because I know they're almost always full of lies (Like swiftboat veterans fo being paid millions by Bush)

The price of gas has nothing to do with what someone drives and everything to do with whether or not the man in the White House has friends like Kenneth Lay

.

The main reasons I'm not voting for Bush are because 1) I want America to be free again, and the Patriot Act is unconstitutional and it makes us NOT free, and 2) I don't like Monarchal Theocracies, I prefer Democratic Republics.

joshhol · #8 11-02-2004, 10:53 AM

I put a plastic rail or two in my 4.5 when I did the head, I don't remember having oversize holes in the rail. The pins fit normally. Don't know what you have going on there.
I'm pretty sure I used the 6 per engine pins for the guide rails. Another thing that bugged me about the plastics is that there is no centering wire on the back.

Tomguy · #9 11-02-2004, 11:43 AM

josh: Maybe your plastic rails were different from the ones I got? In any case, I'll just keep the metal rails in for now I suppose. I do need to do my valve clearances, they seemed to be way too loose on first glance.

300SDog · #10 11-02-2004, 01:12 PM

How many degrees of stretch are you getting? This can be measured by alligning the engine at TDC and then checking the camshaft mark at the stantion, if you arent aware of this already.

Meanwhile the price of fuel remains artificially low so the imbecile Bush has better chance of getting re-elected. In my industry, transportation and trucking, we are getting clobbered with $2.19 prices for diesel. Yet most people believe prices will reach $2.60 by January and then stabilized near $2.25 at the lowest.

Another way to accomodate stretch and chain slap is to see about an offset woodruff key for those European camshafts you installed. And they made a couple of different chain tensioners too: hydraulic and mechanical. Some might have a longer throw than others.

Gone are the days of cheap gasoline. And with the idiot GWB driving national debt through the roof and cutting taxes for the rich, it's gonna be cold day in hell before fuel and road use taxes go down.

And those alloy chain rails can be resurfaced with fresh rubbers. Possibly brake shoe resurfacing company can tell you where this can be done.

ptoro01 · #11 11-02-2004, 08:31 PM

Alright, Please dont be lazy about the chain issue. Purchase yourself a new chain, and new upper guides and a new tensionner. Take a day and rail through your timing chain after you put in new rails and put the tensioner on. If you wanna PM me I can send you pictures of how to do it with simple tools such as zip ties and how to get the tensioner in 1 handed.

I replaced my rails and tensionner early summer but didnt have to complete the chain. My engine has been running like shiat before and consuming crazy amounts of gas at high speeds especially. Not only did I risk getting my engine blown up every single time I started it but I was also throwing away gas money. Just take the time and do it right and you'll be much much happier.
Chainslap is a dangerous thing and can cause you to spend about 1500 to repair if damage occurs. Instead spend 150 bucks and get your engine ready for anotherr 100 000k

Peter

Tomguy · #12 11-02-2004, 09:41 PM

I'm not sure how much stretch, exactly, but I know it's a lot. When I checked it, I wasn't thinking - the crank was aligned and not the cam, so I moved the cam and got about 5° of stretch - I didn't realize at the time that all I really did was move the slop from the one side to the other, essentially throwing my reading way off. I predict about 12° of stretch, give or take 3.

And the chain isnt too important to me because I DO have those metal rails, so the likelihood of them snapping and causing the chain to skip is very mimimal. Plus, I have a set of "Spare" heads that are in almost new condition that I want to throw on it, so I can always put them on if need be (as well as cams in like new condition, if they are damaged in the event of the chain skipping or snapping).

300SDog · #13 11-03-2004, 01:19 AM

Or you can turn the crank a few revolutions eventually getting near TDC and line up the camshaft to its stantion mark instead...... then read degrees of stretch off the crankshaft pulley.

Got new heads and camshafts, huh. I've heard it's a good idea to match new camshafts with their own sprockets..... not to attach old sprockets to new cams.

psfred · #14 11-03-2004, 01:22 AM

The chain will eventually fail due to wear, and more than 12 degrees of stretch is very likely to run the valves into the pistons.

Proper check is to crank engine around until the cam is at the TDC mark (notch in thrust washer aligned with bump on front cam tower), read degree wheel on crank. Gotta do this soon on the 280, I'm very close to 200,000 miles (or somewhat over, depending on exactly how long the odometer was out of order).

The reason that the right cam is later than the left is that there is about 2 ft of chain between them -- it runs down around the dizzy drive gear (aka idler gear) below the valley and the back up to the right cam.

The chain will only touch the guides as is vibrates except for the tensioner rail on the slack side -- that rail is pushed out by the tensioner to pull it tight so it WON"T slap the other guides much. A new one is VERY tight, so much so that it's sometimes hare to get in with the tensioner in. A very worn one will be so slack even with the tensioner full of oil that it will slap on the guides, breaking the plastic ones when they get old.

Peter

Tomguy · #15 11-03-2004, 01:27 AM

Quote:

Originally Posted by 240DieselDog

Got new heads and camshafts, huh. I've heard it's a good idea to match new camshafts with their own sprockets..... not to attach old sprockets to new cams.

Ooops, already have done this twice

Oh well, I'll slap the other cam gears on when I do the chain I guess, they match the cams currently on there

Peter: All I know is that if I watch the tensioner while I crank the engine, I can see it pulsing in and out. I can only assume it's extending about as far as it can go during its highest point.