Mechanical or Hydraulic?

Flying356 · 09-10-2011, 09:33 AM

The tensioners in my 2.4CIS look like they are converted to mechanical. My question, are they still hydraulic with the bolt acting as a stop or are the guts removed to insert the bolt thus making them only mechanical? I have noted a few others on the list making mention of this mod. Thanks for any help,
Christian

Flat6pac · 09-10-2011, 10:13 AM

The insides have been removed and the bolt inserted. Does not keep the chains tight. Replace with the same style hydraulic and use the fail safe collar will work fine.
Bruce

Flying356 · 09-10-2011, 03:41 PM

Thanks Bruce.

daniel911T · daniel911T's Garage

Hey Man,

When I dug into my old motor I found the same thing:

Timing chain and tensioner issues

Those things destroyed my case.

Before you do much else with your motor, give a close inspection to the intermediate shaft, oil pump shaft etc...

In the link, one of the last posts has the post mortem of the motor. Should give you some things to look at.

Avoid those tensioners at all costs!

-Dan

Henry Schmidt · Henry Schmidt's Garage

The key to tensioner survival is replacing the chain wheel support with a wider version.
Even the Carrera tensioners will fail with regularity if you use the old style support.
Our host sell the factory version but when they were unavailable we made our own version.

BTW: For many years race engines have been /are built using the mechanical tensioner. If installed properly they offer safe, reliable performance. Damage to the case is caused by improper installation.

Flying356 · 09-11-2011, 06:45 AM

Thanks Dan!

daniel911T · daniel911T's Garage

Henry,

I totally agree with you about the mechanical tensioners being an OK race part. Those motors are taken apart pretty often, which gives good opportunity to check and adjust chain tension.

I think they are not good for street use, unless you're taking the chain boxes apart all the time to check on them.

-Dan

Henry Schmidt · Henry Schmidt's Garage

I've own a 914/6 for 25+ years and have always run mechanical tensioners in it.
The tensioners are checked only when a noticeable rattle is present. That can take 25K miles to occur. With the collectable 911 Porsches that rarely get driven, the mechanical tensioner is very viable option.
The key is to adjust them so that they are not too tight. What most builders fail to realize is that the chains get tighter when the engine heats up. You must adjust the tensioners so that it's loose when cold. As the chain and wheels start to wear the chain will show signs of being loose but all you get with a marginally loose chain is a slight rattle at start up. By the time the engine is warmed up and ready to run that slight rattle will be gone.

Flieger · Flieger's Garage

Someone should make a tensioner that has the wheel on the outside of the chain so that it pinches the chain together (like they are normally) but with the chain tensioner anchored to the top of the chain housing. Make it out of some Aluminum with a high coefficient of thermal expansion, that way the base will shrink up and make the chain tighter at cold and then when it heats up it will loosen up a little bit to maintain tension. Only then will these really be "mechanical chain tensioners".

proporsche · proporsche's Garage

hello Christian
There is also another way to deal with your chain tensioners.They are pretty expensive lately so you can actually buy rebuild kit for each tensioner.It is very easy to replace and then you have to bleed them.
I have build an 911Sc engine for friend of mine and he has won in Monterrey Calif his category race with this engine.At this time i have put in mechanical tensioners but after another rebuild(after the racing) i have put in factory hydraulic chain tensioners again for that year.
You can also buy up-date kit and put in 1984-89 Carrera Hydraulic chain tens.These are pretty good it keeps the constant oil pressure on them,but not for racing.

proporsche

bullethole · 09-12-2011, 07:09 AM

Why do you say the carerra hydraulic tensioners are not good for racing?

proporsche · proporsche's Garage

i have seen them collapse during a race a couple of times,that is just my experience..but it is everybody`s choise...what they put in:-)
proporsche

Flying356 · 09-23-2011, 12:08 PM

I bought a used set of 930 P/N hydraulic tensioners as well as Porsche rebuild kits. Rebuilt them both last night and bled them and will be swapping the mechanical for hydraulics in the morning. I will also be installing collars as a backup measure. Thanks to everyone for the great advice and all of the help,
Christian

KTL · 09-23-2011, 02:17 PM

Christian,

Do shoot some closeup pictures of the chain box and tensioner area when you do the reinstallation. Looking at your small picture in the first post, it looks like your tensioner idler arm chain sprocket teeth are very shiny. Which would lead me to believe the sprocket is very well worn?

Jon B · 09-23-2011, 11:46 PM

Christian,

Do your idler arms have bushings at the pivot end, as in the photo below? Idler arms in 1970's engines did NOT have bushings, would gall the chainbox shaft and limit tensioner motion. If you're running 930 tensioners and your idler arms are not bushed, you should replace them with the later, wider arms as Henry suggested.

hcoles · 09-27-2011, 12:44 PM

Quote:

Originally Posted by Henry Schmidt

The key to tensioner survival is replacing the chain wheel support with a wider version.
Even the Carrera tensioners will fail with regularity if you use the old style support.
Our host sell the factory version but when they were unavailable we made our own version.

BTW: For many years race engines have been /are built using the mechanical tensioner. If installed properly they offer safe, reliable performance. Damage to the case is caused by improper installation.

Henry, I like that. Make use of supporting area since it is sitting right there unused.