Alfa Romeo Owners Club of Australia Forum

Technical => 160 Series (90, 75, 164 Sedans) => Topic started by: MD on March 21, 2020, 10:08:10 PM

Title: TS TIME BOMB
Post by: MD on March 21, 2020, 10:08:10 PM
If this problem hasn't visited your 8v twin spark engine yet, it's just question of time. It's killed two of my engines. The photos explain the problem and the solution. Take heed.
Title: Re: TS TIME BOMB
Post by: Duk on March 22, 2020, 12:21:22 PM
That's some bad design right there.
But I would stay away from welding. Chances are the sprocket is cast iron and you're more than likely going to warp/bend the shaft.
Having a circlip groove machined into the shaft and using a circlip to keep the key in place is 1 possible solution.
Maybe have the keyway deepened so a taller key is captive within the shaft.
Or a radiused bottom keyway could be cut and a woodruff key used.
Title: Re: TS TIME BOMB
Post by: MD on March 22, 2020, 05:34:45 PM
Hey Dukster. It's been an eternity.
Just to clarify, the TS version has no key-way whatsoever or other captive method of fixing the sprockets onto the shaft other than an interference fit. That is the entire problem.
Other than that, I am not aware that there is any sideways migration of the sprockets along their mutual "axle" and so retaining circlips are not necessary if that is what I am interpreting from your reply.
I believe the sprockets are steel. A couple of small welds would lock them together if you are racing farmer on the go but if you want a more elegant solution go with the Dukster  :)
Title: Re: TS TIME BOMB
Post by: vin sharp on March 22, 2020, 06:53:24 PM
Er, yes a poor design idea particularly when they previously keyed them on all models for 30 years. In theory the interference fit should do the job, but that assumes all manufacturing diameters & bores are correct fit & a large hole/small shaft combo don't come together...
I've not personally seen one come loose yet, but have pinned a couple between the pairs just in case.
The sprockets & shaft appear to be steel & I've used a 4mm dia hardened steel pin to key it in place. This should be sufficient to stop it potentially working loose on the shaft. In both cases I did a test press (in the removal direction) to check that the pair were at least secured well before even bothering to attempt pinning. DON'T block off the oil supply thru the centre of the shaft when pinning!
PS, T/Spark are closer on the chains centre-line spacing, so you can't just toss in in a Nord one unless you can press it apart & machine a face to narrow it.
Title: Re: TS TIME BOMB
Post by: GTV-074 on March 27, 2020, 05:04:44 PM
So whats the best preventative measure to take, or do we just wait until it goes 'boom'?

I am guessing its an engine out job?

I just purchased a TS recently (had one years ago) but haven't got around to doing anything to it yet, so just asking...

Cheers,

Paul.
Title: Re: TS TIME BOMB
Post by: MD on March 27, 2020, 08:53:12 PM
Well the purists would not like it but here's what I would other than the obvious which is to pull the engine down and take the opportunity to fully refresh it to trade standards

Remove battery connection
1 Radiator out.
2 Alternator off
3 Front pulley off
4 Cam cover off
5 Disconnect all hoses to water pump
Undo the two side bolts under the engine head
Remove all peripheral nuts holding on the front cover.
(the fun part starts here)
Remove front timing chain cover. Sump and head gaskets will get damaged in the process around the front cover portions.Don't worry about it. Substitute with a gasket in a tube on reassembly.
Once the sprockets are exposed, clean the contact area between them with acetone (brake cleaner).
Make a small but solid weld between the sprockets at the 9 & 3 o'clock position. ( Be ready to get wiped off Vin's Christmas list for the weld job)  :)
A full weld is not required.

Refit in reverse order and connect the battery.
Personally, I would take the engine out and fix it sweet throughout. Depends how deep your pockets are.

Failing that, do nothing. Nothing may happen, then again do you want to wonder if it will and when?
Title: Re: TS TIME BOMB
Post by: vin sharp on March 27, 2020, 10:00:55 PM
I would be afraid welding in-situ might deposit a stray weld-spatter ball in the timing chain or elsewhere that eventually gets into & stuffs the
oil pump or worse...
Personally I'm not about to break open my T/S because of worry. I've never actually seen one do it (yet). Perhaps you're just extremely lucky to have had 2 of the rare ones MD!  ;)
Title: Re: TS TIME BOMB
Post by: MD on March 28, 2020, 08:41:13 AM
Yes Vin, I must say darn unlucky. Having said that, my European contacts have experienced the same.

Good caution regarding the weld spatter however to get you home from Julia Creek in a dust storm ( :) ) a bunch of wet rags wrapped around the chains and blanking off the sump openings would get the job done. Any port in a storm... :)

Vin. Just doing a bit of lateral thinking, would a roll pin inserted in parallel with the shaft be a reasonable option as it has no chance of penetrating the oil gallery in the shaft?
Title: Re: TS TIME BOMB
Post by: Colin Edwards on March 30, 2020, 10:53:07 AM
Well not exactly a poor design if the repeatability of the respective bore and shaft dimensions can be guaranteed
If the machining acccuracy improved in the later production runs (very likely), doing away with keys and keyways makes sense. 
Lower manufacturing costs due to less machining stages would be developed by the manufacturer.
Not introducing keyways into shafts and bores will reduce the likelyhood of stress cracking.
IF the respective surfaces are consistent enough, very high elastic averaging will result and contribute to a very reliable joint.
No idea what interference Alfa or their parts supplier chose, however 0.1% < 0.15% would by likely.

Could it be these engines that have "failed" have been "tuned"?
Could it be increased loading on this joint due to camshaft design, valve mass and spring rate have increased valve train loads excessively?
Have these engines been over-revved?
Have these engines been over-heated?

I'm with Vin on this one.
Why pull down a perfectly good engine and interfere with this joint when the likelihood of this particularl failure is statistically very low?
Title: Re: TS TIME BOMB
Post by: 105gta on March 30, 2020, 12:33:54 PM
Totally agree Colin, I suggested on the 'other forum' to this situation valve train loading but I don't think I was met with much reception.
Title: Re: TS TIME BOMB
Post by: vin sharp on March 30, 2020, 10:12:31 PM
I have heard of it before on a stock road car, (but never seen personally). 
In theory all should be good, but obviously the later tolerances ARE NOT GOOD ENOUGH & are probably the ones most in need of keyway/keys just in case. Even if over-revs, and or modifications like stiffer valve springs have been made, the things should never be close enough to design margin cause a problem. I have never ever heard of a keyed Nord one even loosening.
The ONLY Alfa cranks I have ever encountered with manufacturing faults ( multi-degrees of out of phase on big ends) is on T/Spark 75s.
The only Alfa conrods I have ever seen fail in the centre of the beam (without any bearing seizures) are T/Spark 75.
The only out of parallel (.006" +) liner-seat diameter to top deck I've ever seen is on T/Spark 75.....me thinks there was a period (FIAT takeover period?) where the quality control was not effective. Not the period to decide to leave a keyway out for the sake of cents...
However, 35 years later & most are probably still in service somewhere without too much problem. Just key the sprockets when you have one apart for peace of mind.
Title: Re: TS TIME BOMB
Post by: GTV-074 on March 31, 2020, 04:04:46 PM
Great discussion Gents.....

Its interesting, the 75 TS seems to clock up some big mileages 2-300K with a seemingly low number of issues.

Whilst looking for mine over the last 12-18 months, the high K's on them seem testament to their robustness but
as Vin notes they do have the odd failure.

MD, any 'pattern' in the failures, like build year etc.?

Cheers.
Title: Re: TS TIME BOMB
Post by: MD on March 31, 2020, 06:42:06 PM
Well dismiss the loaded valve train straight up. Standard, valves and original springs.
High revs? No more and no less than a 116 or 105 engine would normally handle.
Ditto for both engines.
It's a bitter pill but the Bean Counters get the gurnsey.

As for the mileage these engines typically do if they are correctly maintained is usually at least twice the mileage of its carburetted cousins. I put that down to better cylinder lubrication due to fuel injection. Sheit, there better be some compensation !  ;D

No pattern that I am aware of.
Title: Re: TS TIME BOMB
Post by: MD on April 27, 2020, 05:16:09 PM
Here's why it failed.
Title: Re: TS TIME BOMB
Post by: kaleuclint on April 27, 2020, 08:37:00 PM
Thing is -- there are so many vehicles with 'that' issue.  The sixth gear problem in the 159's Getrag box.  A certain BMW motorcycle that needs a groove to be cut in the outlet shaft and a circlip fitted like they used to, or else bearing failure is waiting to happen.  All cheap enough to fix as far as parts go (like a couple of dollars); just they all require hours of labour and/or mucking around to sort out.  All potentially catastrophic if unresolved.
Title: Re: TS TIME BOMB
Post by: GTV-074 on April 28, 2020, 07:49:36 AM
Wow thats really taken a beating.....

Cracks on the gear and the shaft looks all chopped up...

Nasty...
Title: Re: TS TIME BOMB
Post by: Colin Edwards on April 28, 2020, 08:43:20 AM
Hi MD,

Great photos.  Now we are getting somewhere!!

The fractures explain how it failed or at least the cause of the loss of interference fit.  Just now need to explore why did the sprocket boss fracture?

The design in the two most recent images is significantly different to that in the earlier photo.  The sprocket boss wall thickness appears much thinner.  Are these sprockets from similar engines?  Which is the earlier / later design?   Both designs feature "lobes" 1800 apart..........curious!   The failed sprocket "lobes" are significantly smaller than those in the earlier photo.

All other things being eaqual, the failed sprocket is definately more likely to fail exactly as it has than the one in the earilier image.  The location of the fractures is no coincidence! 
Implementing a purely interference fit in this instance is not the issue.  The realitively thin wall thickness of the boss is very likely the issue and possibly the root cause of failure.  The interference fit causing the relatively thin wall to stretch beyond its elastic limit. 

The combination of wall thickness variation and direction of rotation probably determined where the stress is concentrated and where the likely fractures would occurr.  Now if the boss featured a consistant wall thickenss and say the OD was that measured at the lobes............................................!?!




Title: Re: TS TIME BOMB
Post by: Duk on May 05, 2020, 10:59:12 AM
The problem could be a result of stacked tolerances.
Where both the bore of the sprocket and the diameter of the shaft are both within their respective tolerances, but if you did the numbers for the fit, that'd be incorrect.
The broken shaft boss on the sprocket could well have been a result of a fit that was too tight.
That is, the shaft was machined on the high side of its diameter and the bore in the sprocket on the small side of its tolerance.
With the sprocket blank looking like it was cast rather than forged, the grain structure is less dense and more likely to crack.
Title: Re: TS TIME BOMB
Post by: GTV-074 on May 07, 2020, 01:52:29 PM
MD, whats the flip side of the larger failed gear look like?

There is a new one for sale on evilbay at the moment and i'm just trying to see what the other face looks like.

Cheers,

Paul.
Title: Re: TS TIME BOMB
Post by: GTV-074 on May 08, 2020, 03:06:52 PM
OK.... Don't worry... i got which side is which now...

Cheers.
Title: Re: TS TIME BOMB
Post by: festy on July 21, 2020, 07:21:45 PM
Hey MD, your sprocket looks fine to me - but I'll swap you for my slightly used Nord one if you like?  ;D

(https://www.festy.org/pics/albums/userpics/10001/broken.jpg)
Title: Re: TS TIME BOMB
Post by: bteoh on July 23, 2020, 03:15:37 PM
What would cause them to chip like that?  :-\
Title: Re: TS TIME BOMB
Post by: festy on July 23, 2020, 03:41:25 PM
Quote from: bteoh on July 23, 2020, 03:15:37 PM
What would cause them to chip like that?  :-\
The sprocket rotating on the shaft forced the woodruff key to split the hub.
The arrows in the pic below show where the shaft and sprocket *should* line up:
(https://www.festy.org/pics/albums/userpics/10001/rotated.jpg)

Amazingly, the engine was still running like this. I only discovered the damage when I found the missing chunk of the sprocket hub in the sump pan, and compared it to all the misc spare engine parts I had lying around until I found a match so knew where to go looking :o
(https://www.festy.org/pics/albums/userpics/10001/normal_idler1~0.jpg)