3.0 sc timing chain replacement

[GDR]

The timing chains on my 3.0 sc engine needs replacement.
My Porsche parts dealer advices med to attach the new chain to the old, and turn the engine until the new one is fully on, with the chain turning the cam as well. I have not heard of this method before, but it seems like the easiest.
To me, it looks like there is not going to be enough room for both chains ind the housing when doing this.
Anyone who has tried this, or have a better alternative method? I would prefer doing this with the engine in the car.
Thanks!

[Mark Henry]

Pretty sure the person who told you this was messing with you.
Or a dumbass.

[GDR]

Originally Posted by Mark Henry

Pretty sure the person who told you this was messing with you.
Or a dumbass.

He was not messing with me.
Why is this a bad idea, and how would you do it?

[Flat6pac]

The motor is so worn out that you're changing chains? There is more to it than just turning the engine over, the valves have to stay off the pistons and that open chain is pretty long.
What is the reason, the tensioners are fully extended?
Bruce

[john walker's workshop]

You need to remove the housings to do it that way. It's easy then. Turn slowly and when you get resistance from a piston touching a valve, turn the cam a bit until you can continue turning the crank.

[Mark Henry]

OK, I get it, just to feed it through.

[john walker's workshop]

Then reinstall housings, set the crank at TDC @1, set the cam keyways @12 o'clock, install all the crap back in the housings and set cam timing. Doesn't hurt to check cam timing before disassembly, so you know where it was, especially if it has non-stock cams.

[GDR]

Yes, the chain is too stretched and needs replacing.


Sounds good. I was planning on letting the chain turn the cam as well.. Would it not be possible?
Alternatively I could remove all rocker arms, but that is a lot more work.

I have checked the cam timing before, and it is at 1.13mm. Not sure what cams.

Thanks!

[boyt911sc]

Originally Posted by john walker's workshop

You need to remove the housings to do it that way. It's easy then. Turn slowly and when you get resistance from a piston touching a valve, turn the cam a bit until you can continue turning the crank.

John,

How do you get the chain housing off the crankcase with the cam installed? I tried removing the chain housing/s before many times on several occasions during engine teardowns and had no luck. Getting the chain housing off the crankcase studs with the cam installed is next to impossible for SC engines. What is your trick in getting off the chain housing? Any tip from the maestro? Thanks.

Tony

[Forrestkhaag]

On my MBZ SL's, the cambox allowed for using a masterlink to join to the old chain and drag it thru.

For what it is worth, I just removed my Cam Boxes from my 82 3.0SC with the Cams in place. I think you may be reffering to the Cam Sprockets needing to be removed - then the boxes will come off the case bolts. In my case (no pun intended)...er,.... both came off easily after removal of the sprockets as associated bolts, washers and three bolt sealing plate and o-ring.

The issue is how to keep the orientation of the cam sprocket and chain in the precise rotational alignment when reassembling. With the SL's you use white marking tape on both the chain and sprocket and meticulous counting of chain links to confirm that you are in the right place with the new chain once dragged thru.

For the 911, I, for one, will do a full re-timing once the new chains are installed. Too much at risk if off by one link or one pinhole on the cam sprocket....

Best of luck.

[DRACO A5OG]

Lucky, our cars just need to be close on timing adjustment.

Watch Stomski's you tube video, even or especially with his awesome digital tools and percission mounts, he could only get 1.20 and 1.26MM, respectively L & R ( D & P ) sides. Previously my 3.2 cams were at 1.10 and 0.85MM before tear down. She had very good top end but low to mid were doggity. Now she is purrrrfect :-), BTW, mine is 1.20 and 1.26MM now, No it was not planned :-)

Most important is Chain alignment. Mine was off by one shim (too much) on the d-side, can't believe she did not explode.

[Forrestkhaag]

The shims are rated Jack or Queen in the hierarchy of adjustment values and you are right and good to mention here the alignment issue related to shims on the cams is critical and must be measured.

King however, (IMHO) is understanding degrees of wear, stretch, and fatigue on chain, sprockets, and other moving parts related to cam tiiming.

Like people, these things all wear out at differing degrees.

Sidebar: We have all bumped into a high school cheerleader of past experience in a stinking bar on the coast somewhere - then glanced across the room to our lovely smoking hot wife of 20+ years and said... (mentally) ............. Check em' all out and go for OEM parts when your budget will allow.

Stromski is another King in he world of keeping the DYI's from blowing up a 12K motor on initial startup....

[john walker's workshop]

Originally Posted by boyt911sc

John,

How do you get the chain housing off the crankcase with the cam installed? I tried removing the chain housing/s before many times on several occasions during engine teardowns and had no luck. Getting the chain housing off the crankcase studs with the cam installed is next to impossible for SC engines. What is your trick in getting off the chain housing? Any tip from the maestro? Thanks.

Tony

Once the sprockets, retaining plate, tensioner and arm and guide are out, it wiggles right off. Your issue might be the two little alignment rings between engine case and chain housing. If they are stuck in the housings, they don't allow the housing to angle outward enough to clear the nose of the cam. Mini vise grip them off, then knock them back into the case when the housing is off. Never had an issue.

[boyt911sc]

Originally Posted by john walker's workshop

Once the sprockets, retaining plate, tensioner and arm and guide are out, it wiggles right off. Your issue might be the two little alignment rings between engine case and chain housing. If they are stuck in the housings, they don't allow the housing to angle outward enough to clear the nose of the cam. Mini vise grip them off, then knock them back into the case when the housing is off. Never had an issue.

John,

It never occurred to me to remove the alignment tubes/rings. Next time I do an engine tear down, will try this technique of yours. With the alignment tubes or rings installed, there was no room to clear the studs or the cam shaft for the chain housing to come off. Thanks for sharing your method.

Tony

[Walt Fricke]

Reaching back into memory, I believe that when I installed the pressure fed tensioners on my '77 2.7, I also replaced the timing chains with a master link chain, and the engine was in the car so I certainly did not remove the chain boxes.

Note that the chain is under tension on one leg when rotating the crank clockwise (its normal rotation. The tensioners work on the slack part of the chain. So you can remove the tensioners, bust into the chain on the slack part, hold everything taught with your hands (and maybe those of a helper), and slowly turn the crank as the slack part, with its new chain attached, into the bowels of the engine, from which it will emerge as the taught part in due time until you also get it around the cam sprocket and can join the two new ends. Then you can put the tensioners back on, and you are good to go.

That is, of course, after you recheck the cam timing just in case.

I know I did it, and this must be how. What sticks as the hardest part for me was grinding off the ends of a link pin on the old chain - I didn't have a chain busting tool and had never split a chain before. Nor have I afterwards, as work like that has been done with the engine being rebuilt on a stand.

[john walker's workshop]

Not a lot of room in the housings to roll up the new chain along with the old one and orchestrate feeding it through, but obviously possible. Way easier with the housings off.

[boyt911sc]

Originally Posted by Walt Fricke

Reaching back into memory, I believe that when I installed the pressure fed tensioners on my '77 2.7, I also replaced the timing chains with a master link chain, and the engine was in the car so I certainly did not remove the chain boxes.

Note that the chain is under tension on one leg when rotating the crank clockwise (its normal rotation. The tensioners work on the slack part of the chain. So you can remove the tensioners, bust into the chain on the slack part, hold everything taught with your hands (and maybe those of a helper), and slowly turn the crank as the slack part, with its new chain attached, into the bowels of the engine, from which it will emerge as the taught part in due time until you also get it around the cam sprocket and can join the two new ends. Then you can put the tensioners back on, and you are good to go.

That is, of course, after you recheck the cam timing just in case.

I know I did it, and this must be how. What sticks as the hardest part for me was grinding off the ends of a link pin on the old chain - I didn't have a chain busting tool and had never split a chain before. Nor have I afterwards, as work like that has been done with the engine being rebuilt on a stand.

Walt,

I might be replacing a timing chain very soon to troubleshoot the persistence knocking/rattle noise coming for a newly rebuilt motor. I am trying to visualize how you did it with the engine installed. Did you remove the engine cross bar bracket that is blocking part of the chain housing opening? The engine is mounted on an engine test stand and I could conveniently put it back on an engine stand.

What I am interested in learning how you manipulated the two joined timing chains during replacement procedure. With the chain housing removed, it would be simple but with the chain housing in place, that would need some Mc Gyver technique. Did you have a helper? Thanks.

Tony

[Walt Fricke]

I got my 911, a 1977 2.7 gray market car, in late 1984. This upgrade was done maybe late in 1985, or in 1986 (parts purchase records are in storage), so I'm not too clear on details. Obviously to pull the chain housing covers you need to remove the engine tin to the rear of the motor. And the engine mount cross bracket to keep that out of the way - not hard to do with the engine in the car - just prop up the rear of the engine from below.

The chain isn't all that long, and it can be flexed sideways some, so to speak. With the link which comes with this kind of replacement chain, not hard to clip old to new.

with the engine out of the car anyway, and having the tools and experience to set cam timing and so on, maybe quicker/easier (note John Walker recommends this)to pull the chain boxes, but back then I had not had an engine apart, so wasn't going to do something like that. With the tensioner stuff out of the way, there is a fair amount of room in there.

I assume you have looked, with a Borescope (~$100 at Harbor Freight) or mirrors and lights, and confirmed that the chains are both properly on the inner sprocket gear teeth? Doubtless they are OK, or the guy who helped you find the bad tensioner would have spotted this.

[john walker's workshop]

With the crank at TDC #1 and the cam keyways at 12 o'clock, the right side valves are all closed and the left side #2 intake is open, so your only interference is that #2 intake valve. All you have to do when you feel the piston touch is move the left cam enough so you can continue turning the crank, then put the cam back where it was. It doesn't have to be exact, just ketway at 12 o'clock, because you're going to time them anyway.

[GDR]

A lot of great answers and help, thanks! Appreciate it
I have done the left side, with the housings on and the engine in the car. Not much room for the chains, but it was doable. I attached the old and new chain on the slack/tensioner side, and let the chains turn the cam while turning the crank.

I tried the right side, but it did not go as well as the left side. Now I have removed cylinder 4, 5 and 6 rocker arms, and putting the chain on tomorrow. I had no problem removing them, and I would prefer removing the rocker arms to be safe if I have to do this again. Plus I have the chance to install the rsr rocker seals. Should be easy this way. Removing cam gear and having plenty room for the chains in the housing, and not worrying about valve/piston.