Chewed Chain Guides

[niall]

Recently bought a 1975 2.7, its just had new cam shafts, rocker arms and valve guides fitted before purchase. I drove car for 1000 miles with no problems.

Then I heard the engine make a knocking sound recently, very breifly. This sound went away almost immediately and the car sounded and ran fine.

It was decided to drain down oil and inspect screen for evidence of problem.

I found 4 chain guide end pieces broken off at mounting pin holes, and lots of chewed up chain guide plastic gathered at the oil screen.

Is this common if chain guides were not renewed when the rest of the timing gear was?

The engine was running fine and sounding good when run for oil change warm, would the engine have run if there was valve damage?

[ChrisBennet]

I would think the chain guides would have been replaced while you're in there (they're cheap) but I don't think old ones would have broken up like that without some help. I could be wrong.
Any chance that a tensioner failed, new cams were too agressive and hitting pistons, etc?
-Chris

[Gunter]

Sounds like a closer look at the chains, tensioners, idlers, guides is needed. Open the chain covers and check.
It is possible that a tensioner is bad and lets the chain slop around chewing up the guides. Or the studs/nuts holding the guides were left loose.
Does it have mechanical tensioners or upgraded hydraulic Carrera tensioners? Tensioners are important because they take up the slack and prevent the chain from jumping on the sprockets which results in the pistons hitting the valves.
When doing rebuilds, a lot of times new chains are installed on old chain sprockets with bad results. I posted on this last year with pix.

[niall]

It has mechanical chain tensioners, they were not renewed. I dont think the chains were renewed either.

[Miguel Antonett]

Need to open the change covers ASAP to see what's there.

[Gunter]

Mechanical tensioners work alright but need to be adjusted occasionally.
Consider getting the safety collar for them or upgrade to hydr. tensioners.
At any rate, I wouldn't drive anymore until a closer look inside the chain covers. For that, the engine can stay in the car but, if there is any suspicion about the cam-timing, resetting is very difficult without a drop.
If the chains have a master-link, they have been changed at some point.
Make sure when you look inside that the dual chains are in fact running on the dual chain sprockets (Intermediate shaft)
Check the teeth on all sprockets and the gear and that all guide-studs are tight. Installing new guides is a little tricky.
Let us know what you find.

[niall]

I'll keep you posted, I intend dropping the enging to have a good look. I want to check the top of pistons and valves now.

When I warmed it up for oil change everything seemed fine??

If damage did occur to the valves / pistons due to contact, if the chain did move on the spockets, would the engine run smoothly at idle and sound fine when reved up to 3000rpm approx?? ?

[Gunter]

If the cam-timing changed even one tooth, you would hear that horrible clanking noise when the pistons hit the valves resulting bent valve stems.
Before you open the cylinders, have a compression test done by a competent shop. Depending on the results, a leak-down test can determine if the valves are bent (Leaking)
If that is the case, the engine has to come out.
If the numbers are good, do a partial drop.
Open the chain covers and have a real good look.
You obviously need new chain guides and for that the tensioners have to come out. This is tricky because you need to get slack in the chains without losing the timing.
Check the tensioners to see if one has collapsed.
Replacing the chain guides is with the chain in place is difficult.
Ensure that the chains do not jump on the sprockets. Do a search on this board about how people secure/tie up the chains.
Start a new post asking how chain guides can be replaced with a partial drop and the chains in place.
If you can install the guides and things look good, put it back together.

[oldE]

If you indeed have mechanical tensioners, you can secure the chain around the cam sprockets with some zip-ties and relax the tension on the rest of the chain enough to get the guides in & out with the engine in place. However, I would be VERY concerned about bits of guide here & there in the engine.
I think I would drop the engine.
Les

[niall]

Yeah there was quite alot of mashed chain guide material in there, i got a lot of it out by feeling around inside the engine through the sump port.

I found two tiny pieces of metal, they seem to be broken off gear teeth. They only measure about 1/16" in pitch, 1/16" in height and the tooth width is less than 2/16".

Did not think there was any gears this small in 911 engine?

Only thing that comes to mind is maybe somthing like the rev counter drive?

[Gunter]

That brings back bad memories. Could be the top of the chain sprocket-teeth. There is no doubt that a closer look is needed, otherwise, it's just guessing.

[1fastredsc]

Search my name. I found busted chain guides during my top end rebuild and thought that it would be fine to remove all the little bits i found. Well, 1400miles later, lots of noise in the valve train. Took it apart and found that smaller bits that i didn't see managed there way past the oil pump screen and clogged the cam tower spray bars. Lesson learned, don't assume anything, open the case, make sure all the bits are out, then clean every orfice and passage obsessively.

[niall]

I plan to take the heads off now to check valve and piston tops and do a general inspection of cylinders etc while in there.

Will I have to strip down the heads to check/clean out the oil passages for cam shaft, rockers?

By the way after cold start up the oil pressure was taking about 20 to 30 seconds of running time to climb out of the red, could this be a sign that bits have blocked something already or is it normal on old engines for oil pressure to come up slowly when enging is cold?

[Miguel Antonett]

At first start - cold - the oil pressure should be higher than when warm; 20 /30 seconds is just tooooo long for the pressure to built up.
I would check that engine right away, as somebody said before "don't assume anyhting..."

[Gunter]

To get to the heads, you'll have to take the cam towers off which will make the cam-train accessible. Now you can dismantle the rocker shafts to get to the spray-bars. If the passages are clogged there, they are clogged in the rest of the engine.
This is much more involved; as much work as a top-end rebuild with splitting the case.
Get Wayne's book on engine-rebuild from Pelican. You'll need it!
If you remove the cylinders you also might face the possibility of dealing with Alusil vs. Nikasil P/C's re-ring.
Do you really understand how much work is involved with: "Taking a look at the valves/cylinders"????
Why not do a compression test which will give a good indication of the condition of the valves?

Oil pressure: Did the pressure build up faster before you had issues?
If not, the sender may be faulty. However, you have another pressure indication by watching the oil-light in the gauge. This light should go out immediately after start. Does it?

If it becomes clear that the debris from the guides clogged oil passages, then you have to tear down the whole engine because you'll need to get to the passages in the case and crankshaft etc. Big job!

You'll need the book because there are too many issues that cannot be answered piece-meal on this board.

[niall]

Yeah I have the book and I'm aware its alot of work. I'm going to tear it down for piece of mind.

Not sure how the oil pressure on start up behaved previously as I have not had the car long enough.
But the oil warning light goes out immediately when the engine fires up.

[Gunter]

Sounds good.
With a complete tear-down, you'll find out if the head studs were ever replaced and the case "time-certed" (Also called: Heli-coil)
The 2.7's have a Mag case and are notorious for the studs pulling out.
With the cost, and time involved, have you considered finding a 3.0 liter and spend all that money, and energy, on rebuilding a superior engine?

[niall]

I thought about a 3.0 but they are also quite expensive to pick up in.

I now consider if the 2.7 recieved a quality rebuild with the addition of case savers/time certs, hydraulic tensioners, up front fender oil cooler, a complete new pre74 style dansk stainless exhaust system and an air box pop off valve and replace the contact points with a solid state ignition system and uprated coil.

I would have a good quality motor with most of the 2.7L weaknesses modified out of the sysytem.

I just like the 2.7L, maybe I'm mad? What do you think?

[Miguel Antonett]

IMHO I'd still seriously consider the 3.0 instead of the 2.7

[Gunter]

Originally posted by niall
I thought about a 3.0 but they are also quite expensive to pick up in.

I now consider if the 2.7 recieved a quality rebuild with the addition of case savers/time certs, hydraulic tensioners, up front fender oil cooler, a complete new pre74 style dansk stainless exhaust system and an air box pop off valve and replace the contact points with a solid state ignition system and uprated coil.

I would have a good quality motor with most of the 2.7L weaknesses modified out of the sysytem.

I just like the 2.7L, maybe I'm mad? What do you think?

To be clear: Are you saying that this motor has the above upgrades?
If so, do you know if you have Nikasil (Mahle) or Alusil (Kolbenschmidt) P/C's?????
If the previous rebuild was done with the above improvements, the builder should be able to tell you what P/C's you have.
After a serious rebuild, the guides should not have disintegrated; somthing was not done right.
If the rebuild was done properly, and it has the above improvements, it's worth it to continue.
If not, I would not spent anymore time and money on it.

Have you notified the person who rebuild the engine about the issues?