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PostPosted: Fri Sep 08, 2017 8:39 pm 
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Joined: Mon Jan 06, 2014 10:25 am
Posts: 89
Advice from the TR Engine Gurus Needed
Since starting to drive the car to run the motor in I have had a couple of broken rocker arms - exhaust only.
Yesterday I ended up at the local mechanics where we diagnosed the cause as there being insufficient free downward movement of the exhaust valve. i.e on a cold engine when the valve is opened by the rocker fully compressing the valve springs there is no more free travel (as opposed to the inlet valve where it is possible to move it down further) It seems there is no more compression in the auxiliary (3rd spring). Hence when the engine gets hot expansion has the rocker trapped between the valve stem and the pushrod and the rocker finally gives way.
My novice question is it possible to leave out the auxiliary spring and the bottom collar (which is there to centralise the third spring) as this will I think give sufficient free movement?
I presume I can also get a little extra leeway by setting the exhaust tappets a little wider and live with the rattle
The alternative I believe is head off, back to the machine shop that did the unleaded conversion to get him to reset the exhaust insert further into the head. I think this will leave me insufficient time to prepare the car for the trip to Tasmania. I'd like to do a lot more driving than the 300 miles I have managed so far before setting off on such a long trip.
Forever hopeful
Jim


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PostPosted: Sat Sep 09, 2017 1:17 pm 
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Joined: Tue Aug 02, 2016 8:57 pm
Posts: 47
Location: Nowra NSW
Novice engine reply Jim. Although an engineer.
If two have already broken, more maybe ready to break if they are similarly fitted. Maybe the safest bet is to pull the head off and get the exhaust and inlet valves all checked for the correct seat clearance. I'm sure someone would know this or these figures.
If it had enough force to break the rocker arm then leaving it looser would be way too loose when cold and might be hard to determine a correct looseness cold to give good clearance when hot, properly.
Also going on a long run such as the Tassie trip with a possibly suspect engine head is fraught with untold possible misshaps.
You would be better getting the valve seats fitted correctly and go with it freshly done. At least you know that part would be right.
Someone else may have a better idea though. Regards Ian


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PostPosted: Sat Sep 09, 2017 2:52 pm 
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Joined: Thu Dec 19, 2013 3:40 pm
Posts: 105
Jim
Old trap for new players.
The head re-builder should have checked to ensure no spring binding, my head man checks all that and gives me the figures. The total lift of the cam will determine the settings required. If you have a high lift cam or non standard rockers, you will require more travel.
All that being said, it does not get you out of the bind you are in. If it were me, I would lift the head and get the man to do it correctly. Any attempt to get around the problem is fraught with danger and could leave you stranded. Much better to know it is good and run it in on the way.
Get it right and drive with confidence.


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PostPosted: Sat Sep 09, 2017 5:38 pm 
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Joined: Fri Jul 10, 2015 11:12 am
Posts: 12
I am no expert but have put a few engines together and agree with the above. Person doing the head should have checked out before handing back to you. Have the correct triumph exhaust valves been installed in the head or are they "similar"
I should also check the push rods to make sure that none are now bent.
You should be able to get it sorted within 2 weeks, do some trial drives and head to Tassie with confidence.

peter


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PostPosted: Sun Sep 10, 2017 9:14 am 
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Joined: Fri Dec 20, 2013 10:19 am
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Opinion on the weekend away is "why the third spring?". Binding.


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PostPosted: Sun Sep 10, 2017 10:09 am 
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Joined: Mon Jan 06, 2014 10:25 am
Posts: 89
trooo3 wrote:
Opinion on the weekend away is "why the third spring?". Binding.


Before posting I did do some research. After about engine no. 21000 the head was only fitted with 2 springs and no collar on the exhaust valve hence my question. So far I haven't found out if the specs for the two springs on the later motor are the same as the earlier springs.
Does anyone know why the factory went to 2 springs?
When the exhaust valve is fitted without the collar and third spring there is 3-4 mm of free movement which I believe is enough to allow for expansion.
Can someone tell me what is likely to happen if the springs are too weak apart from the obvious valve bounce if the motor is revved hard.
Thanks for all the help so far
Jim


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PostPosted: Sun Sep 10, 2017 11:01 am 
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Joined: Thu Dec 19, 2013 9:35 am
Posts: 59
I agree that spring binding is most likely the problem and found that the spring locating pads on mine had to be altered to prevent this happening also that they were not all the same. Some of my springs were also different?
I also had an issue with the geometry of the rocker to valve relationship due to the head having too much off it and push rods not matching the best rocker travel and also had the push rods binding on the rocker.

Perhaps finding sledge hammer marks on the flywheel gave me clue on how well maintained my car had been in it's past life??

cheers Rob


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PostPosted: Mon Sep 11, 2017 5:18 pm 
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Joined: Thu Dec 19, 2013 3:40 pm
Posts: 105
I agree that you need to check the push rods....odds are one is bent.
The late TR4 and 4A had only two valve springs on both inlet and exhaust. I use the 4A set on my 3A with an early 4 head. They fit with no problems but then again my man did it right the first time He checked both spring loading and binding.
It is a real issue with head re builders. Modern heads are normally OHC so the problem is rare and they tend to omit the spring binding test. The exception to this is if he is an old timer or they are performance orientated.
Like a lot of things today, if you find a good tradesman you tend to hang on to them and wait your turn because every one else is also hanging on to them.
I would expect that the valve head must be poking out the head for it to give you this problem. A new push rod and the valve job done correct may get you out of this predicament.
See you in Tassie.


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