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newly rebuilt TR4 engine misfiring


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3 hours ago, stuart said:

You can do that on a 4a exhaust too.:wacko:

Stuart.

Yes, Stuart is right with the 4A exhaust manifold, the gasket can be fitted 90° wrong and covers parts of both outlets.

This should be visible with the exhaust bolted on the manifold because the gasket has a special outside shape.

Ciao, Marco

Edited by Z320
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compression are 155psi each cylinder, I haveremoved the manifold(yet again) the manifold seating on the gasket looks uniform and there was no change in engine  when testing with brake cleaner before removing.I have tested each cylinder at the inlet port with flow meter and all read the same approx 14 kg/h

 

Edited by mikespain835
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Aaaaaaannnddddd from left field comes the suggestion to check the Stromberg carbs diaphragms.
If split they give peculiar mixed running.

Mick Richards

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  • 3 weeks later...

Sorry for the delay but been away for a while.

Still got the problem. what is baffling me is that looking with the colortune I can see that it is sparking but no explosion ,I have 155psi compression,I can see that there is a spark so would think fuel problem? well the plug comes out sooty black which seems to indicate that there is fuel getting there. If the ignition timing or cam timing were out then surely it would affect all 4 cylinders and why would it fire on all 4 on brusk opening of throttle?

thanks for suggestions and patience

mike

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Lets go back a post to 3 weeks ago. What about checking the diaphragms on the carbs for correct fitment or splits in either of them, they have a tab for correct positioning. ?

Mick Richards

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On 7/15/2021 at 12:35 PM, mikespain835 said:

compression are 155psi each cylinder, I haveremoved the manifold(yet again) the manifold seating on the gasket looks uniform and there was no change in engine  when testing with brake cleaner before removing.I have tested each cylinder at the inlet port with flow meter and all read the same approx 14 kg/h

 

I think Stuart and others were refering to the downpipe to exhaust joint on the double outlet exhaust manifold being fitted 90 degrees out which blocks the exhaust.

Ralph

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Sorry I should have said that the diaphragms have been renewed and double checked ,I will check the exhaust down pipe gasket,I thought we were talking about the gasket between manifold to head thanks will get back with results

 

Edited by mikespain835
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Just checked and it is a 304164 manifold which goes to a single exhaust pipe held together with 3 studs, not like tr4a manifold. Although I have double (and more) checked the float levels at 11/16 inch  ,17mm it still seems that fuel is not getting pulled from the float chamber at idle whereas on a quick blip opening of the butterflies does pull fuel in as it does fire then (as seen with color tune) but stops once the initial change in pressure across the jet normalises-any ideas on this idea? These are the early CD175's that the choke operates a flap that lifts the piston 

as always thanks for your trouble everyone

Edited by mikespain835
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On 8/3/2021 at 2:22 PM, mikespain835 said:

Just checked and it is a 304164 manifold which goes to a single exhaust pipe held together with 3 studs, not like tr4a manifold. Although I have double (and more) checked the float levels at 11/16 inch  ,17mm it still seems that fuel is not getting pulled from the float chamber at idle whereas on a quick blip opening of the butterflies does pull fuel in as it does fire then (as seen with color tune) but stops once the initial change in pressure across the jet normalises-any ideas on this idea? These are the early CD175's that the choke operates a flap that lifts the piston 

as always thanks for your trouble everyone

I have 175CDs on a 2 litre Vitesse, and I had problems getting them running due to wear in the butterfly spindles that they seem particularly prone to. Could this be your problem causing too weak a mixture on idle.

I am convinced that the problem lies with the carbs or an air leak. You have the compression and you have the spark which you are sure is happening at the right time, it only leaves fuel.

The fact that it runs at all means the cam timing and the ignition timing must be there or thereabouts right, why it is numbers 1 and 3 is a mystery, but could be due to differences in the airflow to those cylinders.

If it was me I would be richening the mixture on the carbs as a starting point to see if I could get it running on all 4 on idle then work from there.

Ralph.

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Well Thankyou everybody for the help and advice offered. IT IS FINALLY FIXED. I had rebuilt the engine, new just about everything.As the Triple valve spring set was not available I fitted the supplied double set with corresponding top collet retainers. As I was getting very good (155psi)compression readings it threw me off course.Finally I did a vacuum test(probably should have done one much sooner) the gauge was bouncing from 10 to 17 hg showing weak valve springs. so I checked them and found them to be quite weak. swapped them for a set of original valve springs which are much stronger AND        hey hey runs as sweet as a nut!! the valves must not have been holding closed or bouncing. Did a leak check and all ok.What threw me was the compression check was ok  could someone explain why it resulted in valve spring pressure

anyway thought I would let you all know

Edited by mikespain835
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3 hours ago, mikespain835 said:

Well Thankyou everybody for the help and advice offered. IT IS FINALLY FIXED. I had rebuilt the engine, new just about everything.As the Triple valve spring set was not available I fitted the supplied double set with corresponding top collet retainers. As I was getting very good (155psi)compression readings it threw me off course.Finally I did a vacuum test(probably should have done one much sooner) the gauge was bouncing from 10 to 17 hg showing weak valve springs. so I checked them and found them to be quite weak. swapped them for a set of original valve springs which are much stronger AND        hey hey runs as sweet as a nut!! the valves must not have been holding closed or bouncing. Did a leak check and all ok.What threw me was the compression check was ok  could someone explain why it resulted in valve spring pressure

anyway thought I would let you all know

Thanks for coming back with that Mike, puts it to bed.

Mick Richards

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Very strange. I would have expected weak valve springs to be OK on tick over, and start bouncing when revved up, exactly the opposite of what you were experiencing.

Ralph

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Ralph My thoughts exactly ,especially as the compression figures were very good and balanced ,that is what was throwing me towards fuel problem but hey ho got there in the end .just never experienced this fault before.

 

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Just underlines how itemising ALL changes made to the car is important.

90% of the time it’s a change you made last that causes the problem, even if it’s an exactly like for like component.

Mick Richards
 

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2 hours ago, Motorsport Mickey said:

90% of the time it’s a change you made last that causes the problem, even if it’s an exactly like for like component.
 

Or someone else made whom you thought knew what he was doing. Which you then got the confidence to sort out yourself.

David

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All I can say is do not rely that the superseeded part number is correct which is what I did when you rebuild an engine there are so many parts that are changed from mechanical, electrical, fuel etc the springs were shorter and weaker just relied on being supplied with the correct part and let's face it the engine is fairly basic .I have to admit that I received the parts confiding they were correct for this engine.WRONG.I did not check that the spring pressure was correct. however I do not fully understand-even now-why the compression test was good on all cylinders yet running the valves were not sealing almost that the springs were just closing but the explosion was causing them to bounce. never seen this problem before and none of my freinds have .but just another thing to think of and to take into account

 

Edited by mikespain835
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