Timing chain noise

Good afternoon everyone

We fired up #3666 in order to get it ready for a drive after the carb overhaul and setup. I had noticed a distinctive rattle from the timing cover when we bought the car but discounted it as requiring adjustment of the timing chain tensioners. I adjusted both tensioners as per the service manual however the noise didn't change. I listened on the front cover and heard a distinctive 'knocking' or 'rattle' and it sounded like the chain was hitting the front cover. I removed the rear valve cover for a look and found the chain to be tensioned reasonably and the cam marks lined up.
I am concerned though about the noise and also the movement in the chain and tensioner sprocket. The chain has more side to side 'play' than I would expect to see in a modern type timing chain and the sprocket on the spring loaded tensioner seems to have what I would consider to be excessive side to side movement in it.
What I am asking is the tensioner sprocket movement normal? How much lateral movement should the chain exhibit? Is a rattle type noise from the front cover normal on this engine. If I heard this type of noise from a customers vehicle I would strongly recommend that they not drive it until we found the cause.
I should also mention that the shoe/slider is in good condition and I couldn't see any place where the chain or sprocket was hitting the front cover or block.

Sorry for the long post but I am scratching my head on this one.

Jamie

 

take it to a good mechanic, maybe two or three, and get thier opinion and estimate. Then, decide if you want to tackle it yourself. Good luck
clay

 

Thanks, but I am a licensed tech with 30 years experience. I am kind of looking for an idea of what is normal with this particular engine as every engine family has its own quirks. But this noise and tensioner movement is not in keeping with my experience on any engine including Ferrari

 

Jamie - my experience in owning and rebuilding 3 Dinos, and helping build 5 other Dino engines is that the noise you describe is not normal. What is normal (in my limited experience) is a constant, ratchet-like sound presumed coming from the crank-to-chain-gear interface, a flat-toothed design. An inconsistent rattle does not sound right.

The chain, when tensioned correctly, should not have any lateral movement on the upper cam-end sprocket. When you write that you have tensioned the chains as per the WSM, this leaves a little room for interpretation. What I do is to loosen the tensioner collet, turn the engine with a large (38 mm) socket in the correct rotation for a revolution, then turn the engine in the opposite, incorrect direction for a few degrees. This will cause the chain to push the tensioner gear back into the collet. Then I turn the engine in the correct rotation and the spring-loaded tensioner shaft will "snap" the gear out onto the chain. This is, to me, the correct tension. Before rotating the engine again I tighten up the collet and the stop screw. Of course this is done on both heads.

With your experience I suspect that you have approached this task in the proper way, and that chain tension is correct. The only other thing to consider is that the paddles are loose.

Hope this helps.

Jim S.

 

Jim

Thanks for the input. I have heard Dino engines before although it's been awhile. I do recall a 'whine' from the timing chain. This noise is quite different.

I performed the procedure as you have suggested except for turning the engine in the opposite direction for a few degrees.

I will give that a try in the morning and post the result. I expect that with the rear valve cover removed I should be able to hear the tensioner 'snap' into place. In any event I will recheck the lateral movement after following the added step.

Once again, thank you for the reference and input.

 

Have you checked valve tappet shims? These can make an awful rattle when worn or incorrectly fitted.

 

Its hard to suggest something to someone with your experience but here goes anyway.
Is it just a rattle or is there a rumble as well? Use a stethescope (long screwdriver held with the handle at your ear) Check all around the top of the head, as TonyL says, a loose tappet can make a racket, its unlikely they will all make the same noise, still, you should be able to identify the type of noise. Check the front head the same way. If that is inconclusive, remove rear wheel and check low down in the timing cover area. Look at Omjohn's page at http://www.dinorestoration.com/tavs/TAV5/ for reference. Also while your at it you can check water pump and distributor for weird noises. Hopefully it's just a stuck tensioner.

 

The early (Fiat)-Dino motor used a tensioning mechanism that did not involve springs to set the correct cam chain tension. The tensioning mechanism's gear was pushed by a “Screw” against the chain creating the proper cam chain tension. Chain slack between the cams was then measured to a specified height (7mm) when deflected with a weight of 20 KG (as measured with an ordinary spring scale). (The tensioner was then doubly locked in place with another screw that clamped the tensioner in the adjusted position.)

Perhaps you can check to see if your cam chains are approximately in “spec” using this method. I am not suggesting you use this method to adjust the chain tension, but as a cross check to see if the tension achieved using the “spring” type adjusters found on the 246 engine are reasonable.

Copies of the relevant 206 manuals giving the details are below.

From the “Fiat-Dino” Roadster-Coupe Specifications and Features Servicing Instructions” Fiat Service Department Turin

Fiat Dino Catalog Parti Di Ricambio (VII-1967)
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Jamie - the method that I described, with the engine turned in the reverse direction, provides an important dynamic.

When turning the engine in the correct direction, the tension in the chain will vary depending upon the cam/valve position. You may have tightened the collet at a point where the chain tension was maximum on the tensioner-gear side, but minimum on the cam-crank side. At another point in the rotation the opposite will occur. Hence, rotating backwards allows the spring to "throw" the tensioner gear back at the chain, insuring proper tension.

Try to watch the tensioner mechanism while you rotate the engine correctly and in reverse direction. This will require two people. You will see the snap-back action.

Jim S.

 

I don't care how much experience you have or how many times you have adjusted the chains, never turn the engine in reverse. The tensioners are to take the slack out of the slack side. There is no adjustment on the drive side of the chain, I don't care how much they see a jump in the tensioner. there is no slack allowed on the pulling sides of the chains, to think other wise changes the cam timing.

 

Absolutely NEVER spin it in reverse, I tried once when adjusting the cam timing and I had gone just a tiny bit too far...skipped a tooth on the chain. Luckily only one and no damage since I was not trying to start it and it was not running, rotating a engine in reverse is bad, on this motor, its really bad.

 

I likewise feel turning the motor backwards in the tensioning process is a bad idea. If done as described probably has no ill outcome, it also has zero benefit if all components are in good condition. If not done exactly as described (directions are rarely followed exactly) the outcome could be very serious.

To the OP. You said you removed one valve cover. Remove the other. I am not very concerned about the lateral play you described. I have worked on those since not long after they were new. They have had a reasonably deserved reputation for wearing out cam drive components from their earliest days. Crank drive gears, jack shaft driven gears, lower cam drive bearings and the chains themselves. 4 cam V6 motors have cam drive dynamics that are very hard on the components. From your description I think gears can be ruled out but I have seen failures of lower cam drive bearings produce a chain noise. That leads to destruction of the gears. You need both valve covers off and to have a second person slowly turn the motor several degrees forward and several degrees back. Look for a delay in the movement of any of the components and look for tilting or shifting of the lower gears. And never ever count on the collets to keep the tensioners in place. That has led to a lot of bent valves.

 

I agree 100%. I hope not, but does seem from the description, to be more than just a chain adjustment. My car suffered the fate you described and the lower idler bearing failed. I was lucky to get away with bent valves.

 

How do you guys really feel about turning the engine in reverse?

I appreciate your concerns, but have never had difficulty. As mentioned in my description, turning the engine a few degrees in reverse simply to allow any slack to be taken up by the spring will not cause harm, nor does it change cam timing. Upon completion of the tensioning process and tightening of the collet I always rotate the engine a few turns and check cam alignment, never to have found a deviation.

Absent this procedure you may be tightening the collet at a point of maximum slack in the pull-side of the chain.

Your collective admonition is received with appreciation.

Jim S.

 

The only way I've ever done it is to start with a cold engine. back off the locknut and turn the engine a few times and tighten it up. Now this is where it would get interesting for some folks but with no other way to turn the engine easily, I would disconnect the ignition and turn it over two or three times with the starter.

 

Dignini - now that is interesting. If you do it slowly by hand (with a helper) you will note that the tensioner rod will move in and out of the loose collet as the engine is turned. This results from different "energy" levels of the cam springs as the lobes press the valves down. Using the starter I can envision a scenario where the engine comes to rest with the tensioner gear/rod pressed towards the collet. Should you tighten it at this point you will surely have slack as the engine rotates. Better to rotate by hand (with a helper) as you peer down the head and watch the tensioner gear. Then, at its greatest travel away from the collet, tighten it down. This is essentially what I do when backing off a few degrees and allow the spring to snap the gear out to the chain, thereby removing all of the slack.

Jim S.

 

Good afternoon everyone,

I would never as a rule rotate an engine in the opposite direction of rotation for the reasons stated by several of you. In this case while watching the chain while my son rotated the engine 'backwards' several degrees and the tensioner pushed in to the point whereby the chain could have jumped had we continued turning the crank. In any event I followed Rifledrivers advice and pulled the front cover to have a look. As with the rear bank the chain is reasonably tight and the cam marks line up properly which says to me that the chain isn't stretched beyond spec. I looked for 'lost motion' while rotating and didn't really see any. I also pulled the alternator belt off to be sure that the water pump wasn't contributing to the noise and the noise is still there.

Using my 30" phillips screwdriver as a stethoscope I can here the noise to the left and right of the water pump. If I didn't see that the chain was tight I would have assumed that it was hitting the cover.

In any event this is my business partners baby and I told him when we bought it that I was uncomfortable with the noise. In any event the engine has a couple of oil leaks and I have convinced him that it needs to come out and repaired before he considers driving it.

Thank you to everyone for there input, I will keep you posted when I get the engine out and apart.

 

Those tensioners should not do that. They should be locked in place and you should be able to turn the motor backwards. The spring action is only for adjustment purposes, it is not capable of keeping the chain tight during running. If the tensioners are moving you have probably found the problem.

 

I just went through all of this. I recently put on my front cover, chains & water pump etc. Do you think that the water pump bearings are going & therefore causing the impeller to rotate against the cover? This happened to my car & left pretty deep score marks on the face of the front cover & behind the water pump impeller. It must have made quite a racket but I pulled the car apart before I drove it too much. Good luck

 

Clearly as valves have not met pistons, it works for you, and this engine its very forgiving. It is a pretty simple set up, a spring and loaded plunger with a sprocket at the end, which just pushes against the chain, within limits its a constant variable. The chain itself canbe a variable and add to the mix. But the chain will never move enough to jump a tooth or slap the sides...if it ever became that loose, the engine would turn only once...maybe.

 

What kind of noise? Indicative of bearings gone bad? There bearings left and right of the pump. If the noise is on the same both sides, then it is unlikely to be the chain or tensioners as both would have to fail in the same way. Equally, I doubt if it is the main drive sprocket bearings as they would have to fail at the same time. So it could be the center bearing on the crankshaft...don't know what it's called, that transfers drive to the chain sprockets. Its failure would transmit the noise and vibration to both banks.

I suppose we will have to wait until you strip it.

 

Dignini and others - I've not done a good job of articulating my thoughts on the chain-tensioning process.

First, there is no center bearing. There is a gear on the crank that mates with two chain-drive gears. These chain-drive gears are held on a shaft suspended between the block and a bracket (or bridge as sometimes referred to). There are two ball bearings holding the shaft of each gear. These can make noise as they approach their failure point.

Second, during normal operation, the chain will have variable tension owing to the position of the six cam lobes pressing down on the valve springs. I refer to this as different energy states. Left to rotate without resistance, each cam will seek the lowest energy state. Alternatively, when constrained by the chain and associated mass of pistons and crank, the cam will stop anywhere.

Thus, when rotating the engine in the proper direction with the collet loose, the chain tension on the tensioner side of its travel will vary, and the tensioner gear and collet will travel in and out. As mentioned previously, it will not, should not do this under normal operation, but will when the collet is loose.

Third, if during setting of tension the engine has come to rest at a point where there is maximum tension on the tensioner-gear side of the chain, the tensioner gear, when the collet is loosened, will move outward, into the collet. Normal procedure will then call for tightening of the collet and (if present) finger tightening of the stop screw. However, when the engine is not turned to the next energy state, there will be excessive slack (or perhaps not slack, but less tension) on the tensioner-gear side of the chain. The net effect is that the chain tension is less than it should be.

My procedure of turning back a few degrees causes slack to form on the side OPPOSITE the tensioner gear, and maximum tension on the gear side, thereby pushing the gear ALL THE WAY INTO THE COLLET. Then when rotating in the proper direction, all of the slack that was on the wrong side is now taken up by the tensioner mechanism with a sharp expansion of the spring.

Hope this helps. As I mentioned earlier, I do recognize the concern over turning backwards, but when doing it by hand and observing the chain and tensioner I have not witnessed any cause for alarm.

Again, the collective admonition is appreciated. I put my pants on left leg first; how about you?

Jim S.

 

that's what i meant to say!

When adjusting the tensioner, one loosens it only just enough to allow it to move.
The retaining nut should be unscrewed only one to two turns, is that enough to loosen the collet?

This is the bit that has me puzzled, how much are you backing off the tensioner nut, not in a rebuild, but in service mode.

 

Dignini - The large collet hex nut should be loosened as much as possible. This insures that there is no binding between the shaft holding the gear and the collet jaws. In fact, you can take the nut off of the threaded flange, albeit you will have spring tension making it challenging to get it back on...not impossible.

The stop screw - a modification on early cars and standard on later cars, should be unscrewed all the way to allow complete freedom for the shaft to slide as deep as it wishes into the collet cap. It is, as you suggest, likely that the shaft will move out of the collet and take up wear-related slack, but my method (right or wrong) of turning the engine backwards will force the shaft much deeper into the collet cap for a moment. The stop screw will prevent this, and hence the reason to remove it, or at least unscrew it most of the way. By allowing the shaft to go deeper into the collet cap for a moment minimizes binding of the shaft and the collet jaws when tension is applied to the chain.

Hope this makes sense. It's one of those things that only makes sense when you are sitting over the head and performing the procedure. Those reading this but not tensioning this month must be quite bored.

Jim S.

 

Jim,
As with everyone one of our lively discussions, this is most interesting and informative; I am anything but bored. Regarding your somewhat controversial technique, it seems to have been successful on eight Dinos. 'tough to argue with success.
We all know that 'The Book' leaves a lot to be desired. Thanks to the sharing of experience by the members of this forum, we have been able to fill in the gaps and keep these jewels running better than, and far beyond, factory expectations. I appreciate all who have thrown their two cents at this topic. My learning curve is still steep.
Coop