Interesting finds at My rebuilder. 2.7

Crashly · 02-07-2008, 10:40 PM

I stopped by my rebuilder today to review my torn down 2.7 and I found a few intereting things that I thought a few here on the board could use and or comment on.
1. Both intermediate chain gears were missing about half of their teeth.

I dont have a clue as to what caused this.
2. The exhaust vale guides were extremely shot. This whole rebuild started as a clapping sound that one of my #1 valve was making. Now that everything is torn down I had a chance to inspect the guides before they were removed. One of the guides had worn so thin on one side and there were two cracks where the thinned out bronze was. I am very lucky that I did the rebuild now. I would highly recommend that if anyone has a lurking feeling about the tightness or looseness of the exhaust valves check them. Pelican parts sells the tool to remove the retainers and the spring with the motor in the car. It is a fairly easy project to do when you are doing a valve adjust. It is a little frustrating but definately not rocket science.
3. Three of my piston tops had love taps from the valves. I could see where the carbon was missing. Fortunately no real damage. Is this caused by the loose valve guides?
4. The bottom end bearings looked extremely good for having 125K. An interesting note. Before my rebuilder tears down a 911 he checks the torque on all of the case bolts and head bolts. On my case he fond a few bolts that were quite loose and he found a few head bolts that were quite loose. This loosness can usually manifest itself in the bottom end wear and contributes to the case halves coming out of round. I ditched the bullet on this one while my case bolts were loose, the case did not significantly shift

.
5.No pulled head studs. Now check this out. This was a CA car that had the 5 blade with thermal reactors until around 115K. The car was originally from the Montery area. I dont believe that there was a lot of sit and wait traffic for this car to have lasted that long with the thermal reactors and 5 blade.
6. Pistons and Cylinders. They looked great. There was very slight wear on the piston skirts but other than that... nothing. I know a lot of people here say that you can not reuse alusil. Fortunately I found a rebuilder that has been around since before alusil was being used in Porsches. When it was introduced he was able to go directly to the manufacture of the alusil plating process and they sold him all of the proper tooling and honing to reuse alusil. Time will tell

Overall I was pretty happy with what I saw considering the age of the motor and all of the Smog junk that was on the Motor.

dtw · 02-08-2008, 05:26 AM

1. On the cams or on the intermediate shaft? Either way, it sounds like your chains were extremely worn, and/or your sprocket depth may have been set incorrectly, causing side loads on the teeth.

2. Welcome to 2.7s. Mine were extremely bad too. NOT good guides in these heads.

3. Sounds like an over-rev at some point. Potentially related to #1?

Crashly · 02-08-2008, 07:14 AM

All of the missing teeth were on the intermediate shaft

boeing 717 · 02-08-2008, 07:19 AM

Crashly are you saying its fairly easy to remove and replace a valve and guide with the engine in the car????

Thanks
JERRY

coachk · 02-08-2008, 08:00 AM

i've a fairly tired 2.7 as well..... did you take a compresion check before the tear down and if so what were your numbers?

afterburn 549 · 02-08-2008, 09:45 AM

The guides ware out in the 2.7 @ a fast rate ( they wont after new ones installed )
You need all the updates on the 2.7 no matter what
you kissed the valves because the guides were so worn they were swapping holes..LOL
Make sure your sprocket alinement is correct ( do not count it as right from the last time)

cgarr · cgarr's Garage

If you let the guides get too bad they can beat the h@ll out of the seats and they will not take a cut, thus new seats.

safe · safe's Garage

Did you have masterlink chains (replaced chains in the past)?

Crashly · 02-08-2008, 08:32 PM

I did have masterlink chains with carrera tensioners. Is this what destroyed the gears?
The valves can not be removed without disasembling the motor, however the intake and exhaust valve keepers and springs can be removed with the motor in the car. Here is a link to the tool:
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911M&section=ENGwiz&page=2&bookmark=13&part_number=PEL-TOL-P7E

I simply put my piston to TDC, Removed the upper and lower valve covers. Loosened the valve adjustes and loosened the rocker shafts and pushed them out. The tool bolts to one of the valve cover bolts. FYI there are seperate tools for the inatke and exhaust. Then they simply push down on the valve spring retainers and expose the clips that capture the valve. The clips are a bugger to remove and I used a magnet and numerous jewerler size screw drives a long tweezers abd bent needle nose pliers. Once the clips are off you just loosen the tool which allows the spring to come off of the valve. Once removed I simply pushed my valve in until it touched the top of the piston then I started to wiggle it. It is fairly obvious which ones are worn once you have felt a tight intake and a loose exhaust.

My compression numbers after sitting a few years without being started and cold were:
3.126 6. 129
2.110 5. 105
1.105 4. 126

Once I had the motor running the compression numbers quickly came up to the 120-135 range. I felt the numbers were decent given the age of the car and the fact that the car had been sitting for over two years next to the ocean without being started. Originally I had hoped that the motor still had some life left in it. It started really good, and did not have excessive smoke at start up. But it did have a noise that was in the valve train on the #1 cylinder that could not be adjusted out. I bought the tools expecting that I would find a broken inner spring and I found something completly different. The tools cost a little over 100 dollars and I feel for a one time use they were worth it, as they allowed me to asses the top end of my motor without having to hire it out to a mechanic and then have to trust his judgement. I am sure that the hourly charge that a mechanic would have charged would have been way more than the cost of the tools. I would highly recommend it if you are having doubts as to the condition of yoyr valves. A dropped valve would have probably been another 1500 or more on top of the existing rebuild.

Crashly · 02-08-2008, 08:42 PM

I do not know if the valve seats will take a grind. I would guess that the seats could become work hardened if the valve closes unevenly. I know for a fact that MY #1 piston ran for about 2500 miles with the clacking sound . I completely agree with the 2.7 needing all of the aftermarket upgrade. Unfortunately mine did not receive them until 115K. (oil cooler, SSI, and 11 blade). I am not sure as to when it received the carrera tensioners and cam chains. I just hope that with the updated valve guides and all of the other mods, that I can get another 125 before the next rebuild.

afterburn 549 · 02-08-2008, 11:44 PM

The Deal..If a seat is hammered..in the big picture it is not that $$ for a seat, and I do doubt that they are all shot.
You will need new guides, and anymore it is a wast if time to face valves, They have the hardest time of any component in the entire Eng. One of them lives in HELL and both open and slam shut several times a sec. If a Valve "drops" it sort of destroys your Eng.
I am NOT bad mouth a mag case guy (*as you see i own one ) With proper updates it will serve you well......peo will tell you go buy a 3.0 or what ever, but if it is tired.....you have to O.H. it anyway, now your out what the machine work and more would have cost you to fix your 2,7 so consider that.
If you are determined you can save a bunch of $$ and do allot of the work your self.
Do not skimp on the case halves they need a total massage , ( oil update , line bore , decked etc) BTDT

safe · safe's Garage

Quote:

Originally Posted by Crashly

I did have masterlink chains with carrera tensioners. Is this what destroyed the gears?

Probably.
It's a strong argument that a new chain on worn gears will destroy the gears.

dtw · 02-09-2008, 03:46 AM

I agree w/safe - but just want to clarify that it is not master links versus continuous chains that destroyed the gears. However, master link chains are proof that the inner sprockets were not replaced.

afterburn 549 · 02-09-2008, 05:19 PM

Also proof some one screwed with it that did not know what they were doing... JMO

dtw · 02-09-2008, 07:23 PM

afterburn - agree 100%. Brings up the question, if crashly doesn't mind me going off topic a little bit. When is it appropriate to use masterlink chains - or in other words, to replace the chains without replacing sprockets? Would be interested in hearing J. Walker's opinion on this one, and any other production shops...

Crashly · 02-09-2008, 08:35 PM

Ok Ill bite. So how did they screw up when installing the chains? Its would seem that they were not aligned some how. But how?

Walt Fricke · 02-09-2008, 09:25 PM

Missiing IS chain teeth is bizarre.

My understanding is that if you are off by more than a couple of shims on the chain gear alignment you will hear it. You may not know why there is that noise, but you will hear it. Maybe even hear/see/feel it when manually rotating things while setting cam timing.

Be that as it may, why would anyone pull go so deep into things as to fuss with the shims if only replacing a chain and adding Carrera tensioners? Might loose timing and reset it, but no reason to do more than pull the big nut.

If it was alignment then the cam gears should look awful too, and maybe the idler as well.

Perhaps the engine had a previous rebuild, or at least top end rebuild? But you don't think so based on what else you know of the engine (and the substantial guide wear). And good looking main bearings aren't an indication of a rebuild - mine have always looked like I could reuse them. Which is why I have a several bags full of them, since of course I don't take the chance.

I'd suggest that the contact with the pistons might have been due to the chain skipping timing, which one might expect if teeth were missing.

When my aluminum IS gear stripped teeth all 12 rockers broke instantly, but that's a different deal.

I once had a cam sieze. This caused the teeth-like bits on the cam timing setting inner piece (some have only half holes serving the Vernier function, looking more like a gear than a full circle with complete holes) to disappear. Chains are strong, and it was really siezed up hard.

Sounds like you have a mechanic who can give you good advice on what to replace and what to keep.

Walt Fricke (puzzled about those gears)

JFairman · 02-10-2008, 08:19 AM

When splitting one of those cases leave the main bearings in till you've cleaned it up and looked at them real good.
If the wear mark from the crankshaft is even then thats good.
If one edge is worn or polished more than the other it means the case has warped from heat and it will have to be line bored and machined, or replaced with a good used one if thats cheaper.

afterburn 549 · 02-10-2008, 05:44 PM

What I think I know. It would be near a miracle if your cases were to be strait.
The bad part is not the $$ for the case work....at last count was 400.00 bucks for O/S bngs (main)

Crashly · 02-10-2008, 06:57 PM

I just read a interesting post about why the intermediate gears went out. Basically the new chains did not match up to the old gears, and then the new chains chewed up the old gears thining them out then eventually breaking. A similiar problem happens when the chain and gears are not changed in unionson on Motorcycles. The cam gears looked great. The mains had no side to side wear everything is nice and even. My rebuilder before the case was torn down, said that we would probably put oversize bearings, however once he tore it down and saw that there was no obvious bearing wear, he feels that a simple bolt together and a standard size line bore will shape everything nicely. At this point I have to trust his judgement, he has a good reputation from the Pelican Board and he has over 60 years of experince. (He started working in a machine shop when he was 13, now he is over 70)