Timing chain and tensioner issues
 

Hey Everyone,
I have a '69 T with a '70 t motor. I just opened up my chain covers with the intent to install a set of collars and replace the gaskets, but what I found in there shocked and confused me. :eek:
http://forums.pelicanparts.com/uploa...1283640231.jpg

I have no idea what this tensioner is. It looks totally different than the pictures in Wayne's books.

There is also a lot of slack in the port side (driver's side) chain. With the idler arm against the top of the chain housing (full deflection) the chain is still slack on top. I don't know if I need new chain tensioner, but in this case I don't think it would help because there isn't enough travel in the idler gear to get the chain tight.

http://forums.pelicanparts.com/uploa...1283641673.jpg
http://forums.pelicanparts.com/uploa...1283641873.jpg

Is it possible that this is a stretched chain, or could there be something much worse trouble causing this? :confused:

I know many will say this is a perfect opportunity to go to carrera tensioners, but I simply can't afford them. I have to work with what I have.

Thanks for the help!

Dan

If the idler arm does not have enough travel, then the chain links have worn on the roller shafts between them and the links have gotten farther apart. This is what the "stretching" really is. You will need to replace the chain and sprockets, as they all wear together. Mixing new and old will lead to accelerated wear and possibly more noise.

The tensioner youre looking a is mechanical. They are race application, not good for the street because they are set correctly only one through the heat cycle. Your idlers are all the way to the top of the chain box so if you replaced the mechanical with the older hydraulic and guard you would still top out against the chain box, your chains are too long and need replacing. They do make snap link chains for your problem but a pain to change and the thought comes that if the chains are worn out, so is the engine.
The snap link chains are about $60 each and it will give you life until you can do something else. You can buy good used early tensioners (pre 83) on the Pelican here. The tensioner guards are necessary but harder to find. Remove all the chain rails when you change the chains, its just easier and lock the lock in the direction of the chain travel.

Bruce

Can you tell me more about the tensioners I have pictured? Do they have any kind of spring in them? Can I consider them serviceable, or do they need to go? Do they have any redeeming qualities?:confused:

I think I'm going to need to replace the port side chain, and the part is already in my Pelican parts basket. If I change this chain, will I have to set the cam timing? :eek: Is there any way to avoid that painful process? It looks like that is going to be a challenging job: any words of wisdom?

The starboard chain seems just fine, can I just leave it alone for now? (with the possible exception of a new tensioner)

Thanks again,
Dan

Get your self a set of useable tensioners, pre 83, the mechanicals that you have are the probable cause of your problem and youre going to have to do something about chain length so its a catch 22 anyway you go, there is no conservative way out.
Another thought, just close it back up and run it, youre not going to jump time..
Bruce

Bruce,
After sleeping on it, I think your advice about just running it is going to be the best choice for me. I already see a few other issues, like some significant wear on the intermediate shaft gear, that indicate the motor is tired. At this point I think I'm better off saving the money and effort for a future rebuild.

By setting the tensioner all the way at the top, so it's touching the chain housing, there is much less slack than there was when I opened it. This motor only has to last a bit longer, probably 10K ish, and considering how long its been running with a really slack chain, I figure it will do just fine with a very slightly slack chain. ;)

Is there any harm in running with the idler in contact with the top of the chain box?

Assuming that I'm just going to run it, is it still a good idea to change out to spring loaded tensioners?

Thanks!

Dan

Youre not fixing anything so just leave everything alone, the mechanical tensioner, which is probably the cause of the extensive chain wear, just dont bother them, loosing wont do any good and tighter wont either as you are against the box, there is no where for anything to go.
Bruce

Thanks for the help Bruce and Flieger!

I'm running it as it is. Now back to eradicating oil leaks... the whole reason the engine was out of the car in the first place! :)

-Dan

Uhh, do you mind if I offer a second opinion?

Probably the #1 cause of catastrophic engine failure in the lifetime of the 911 engine is chain tensioner failure. You have been fortunate enough to catch somebody else's hack repair (the screw in the 930 tensioner) in time to avert this-- "run it" is not the right answer.

You need to do this right: you need a master link chain and new chain ramps to begin with, along with the cam timing tools and a dial indicator and z-block. Set the engine to #1 TDC with the Z1 mark opposite the notch in the blower housing and the ignition rotor pointing at the radial line on the distributor body. Lock the flywheel at this point and DO NOT MOVE the crank.

You should remove the old chain, don't get filings in the oil, and change out the old chain ramps, and install the new chain. With the new chain on, you should be able to evaluate how much wear you have on your sprockets. If there's a great deal of slack in the chain, you have the option of changing the cam sprocket or the idler sprocket or both. (Changing the intermediate shaft sprockets require splitting the case)

Our host can supply you with new 930 tensioners which can be easily reinstalled. The advantage of the spring-loaded tensioners is their ability to take up the slack in the chain as the sprockets and chain wear over time. It's true, race engines use solid tensioners for reliability and because they get torn down every 20-50 hours anyway.

If you get lucky it's a couple hundred dollar job. If you aren't lucky, it's a couple hundred more for sprockets. If you keep it as it is and the chain jumps time because you are out of tensioning range, it's a few thousand dollars minimum to say nothing of the damage to other components.

Not trying to be the prophet of doom here, just offering you another opinion. Good luck!

He will not have a chain tensioner failure with this set-up. He may however have a chain fail in the near future due to excessive chain wear.

-Andy

I'll offer a 3d opinion: take the tensioner out and take the idler arm off and inspect it carefully. I have one in my collection which developed a crack, which caused the arm part to move up at a greater angle than it should be. While I caught mine before it was all the way up to the top of the chain box, it was still way too far up.

At my last race a guy had the idler arm break. The results were not pretty.

You can do this without changing your cam timing at all. Just tie the upper and lower runs of chain together with some wire or something if you are otherwise worried about this. It takes quite a bit of slack to skip a tooth with the engine stopped, and you can easily avoid that.

If it is cracked you know what to do.

Were this my engine there is no question what I'd do: I'd replace the chain, and the tensioners too. Setting cam timing is not all that tough. See if somebody with the tools on this list lives nearby and will help. This is ridiculously out of whack. I'd take a look at the cam gear to see if it was atrociously worn, and replace it if so (after all, to replace the chain you pretty much have to reset the cam timing.

Or at least check the timing - you want to use the old chain to pull the new chain into place, using the link which comes with the new one to join temporarily the two. If done just right you may be able to keep your timing. Though if it is chain wear which caused this your cam timing is out of spec some.

Those tensioners you could keep until you decide to build a race motor. They also can be used when you are setting the cam timing, as they can be cranked up to take all the slack out of the chain when doing the timing, and then replaced with proper hydraulic ones.

I'm a bold corner cutter, but I don't think I'd run an engine like this.

Walt

A close look at the idler sprocket in the first picture shows a very worn sprocket.
The second tooth up from the chain appears to be worn significantly shorter than the adjacent teeth.
This engine is begging for at least new sprockets, including the intermediate drive sprockets, meaning splitting the engine.
These engines don't wait for a convenient time to wear out. Continue to run it at your own peril.

Final update on this issue
 

First of all, I'd really like to thank all of you for your great advice, and all the generous offers of help! Owning a car like this would be next to impossible without such a supportive group.

Here's the post-mortem:
When the tensioners were installed, long, long ago, the left side chain was set tighter than the right. This caused a significant side load on the intermediate shaft which has done severe damage to the case. As the shaft dealt with the side load, it actually deformed the case at the bearing holes, making both holes into ovals. The left chain may be stretched, but it would be nearly impossible to tell, as the real problem is that the intermediate shaft is actually misaligned, causing the left side to be closer than the right. This misalignment has caused other significant issues, such as the aluminum intermediate shaft drive gear is not mating correctly with the crankshaft and is damaging the teeth and shedding material. The hollow splined shaft that runs the oil pump is also cracked all the way around and has a large wedge missing at the intermediate shaft spline. This case had already been modified to accept intermediate shaft bearings, and due to the enlargement of the holes, you can even see the bearing with the case still assembled.

So, the case is a total loss, the entire cam timing system is destroyed, the intermediate shaft is destroyed, and I've decided to abandon this particular motor.

The real tragedy about this is that the car ran when it went into the garage!

I've already purchased a pretty fresh, identical longblock from another Pelican, and I'm eagerly awaiting it's arrival. I've also invested in Carrera tensioners, and a new set of chain ramps, as I don't ever want to see anything like this again! I have a beautiful set of freshly rebuilt Webers, a new clutch and resurfaced flywheel, rebuilt alternator and starter, repainted tin, an awesome centrifugal fuel pump with a PMO regulator, the correct distributor, and a bunch of new gaskets and seals to make the new motor feel loved in it's new home. I hope I'll be able to get to installation pretty soon.

I'll be dissembling the old motor and selling the good parts, like the heads, pistons and cylinders, crank and rods, and whatever else can be salvaged. Compression was good on all 6 the last time I checked (about 1000 miles ago.) If anyone out there wants a set of mechanical tensioners for racing or something, I'll be happy to sell them cheap. I haven't listed in the marketplace yet, but if you have any requests for parts out of a 2.2T longblock, just let me know.

If any of you happen to live in the greater DC area, I could really use the help with engine reinstallation. I'm down in Woodbridge, VA. Thanks in advance!SmileWavy

I'll update this post with pictures tonight.

Thanks again for all the help!
Dan

Well, you will have an interesting coffee table base there. :(:rolleyes: Now you will have a chance to build a motor exactly how you want it.

Dan,
I'm sorry to hear your engine problems are so severe. Mechanical chain tensioners do have limitations.
It sounds like you are on the right path with another case.
Thanks for the follow up post. I'll be looking for your next update.
Have fun, take your time and good luck.

Daniel

Thanks so much for the detailed post-mortem. I don't think any of us who contributed to this discussion thought of the cause you found! In our defenses, I suppose those of us not in the trade would never have made that kind of huge mistake assembling our motors. And maybe the professionals, who see the results of numerous mistakes by others, had not seen this one either.

Now we all have another cause we can associate with those symptoms.

Your good sense in disassembling the motor saved you much grief. When that splined connector broke, you'd have had no oil pressure, and who knows how long you might have run the motor that way.

But it might have been worse if that overstressed aluminum IS gear had given away. I had one strip teeth. Instantly broke all 12 rocker arms. Don't recall how many valves were bent.

Walt

The pictures of Post-Mortem
 

Here are a selection of the pictures I was able to get of the damage done to the engine by these tensioners.

http://forums.pelicanparts.com/uploa...1286409607.jpg

above shows the long radial crack on the shaft



http://forums.pelicanparts.com/uploa...1286410025.jpg

Above is the chunk missing out of the spline, the pointy end is the start of that long crack.

http://forums.pelicanparts.com/uploa...1286410130.jpg

Above is a good shot of the case damage. Note the bearing just hanging in space.


http://forums.pelicanparts.com/uploa...1286410304.jpg

This is a poor picture of the drive gear. If you look closely you will see galling and shreds of Al on the tips of the teeth.



http://forums.pelicanparts.com/uploa...1286412954.jpg

Finally, notice the notch the chain has taken from the tensioner mount.

It probably goes without saying, but the motor was in this condition when I purchased the car. I have no idea how long it was running in this condition. It was even seen by a couple of reputable Porsche mechanics in Oregon. They said there was a bit of chain noise, but nobody ever even dreamed that it would be this bad. My quest to fix oil leaks was the first time in untold miles and years that anyone was deep enough into the motor to catch this stuff.

I'll post more pictures as I disassemble the longblock.

Thanks again for all the support!