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newly rebuilt TR4 engine misfiring


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HI everyone,

I have just rebuilt a TR4 engine and have a misfire on No 1 cylinder .compression checked at 140/50psi  double checked tappet clearance.Slight bow in inlet manifold corrected by machine shop after doing spray test .Plug sparking and new  .Changed actual distributor with new points and condenser and rotor,Changed cap leads and caps after 50 years of experience never come across this. It has twin zenith cd175 strombergs.Timing checked half a dozen times .Blanked off servo take off no change.Also this has changed from misfire on 3 to misfire on 1 Any help /ideas will b e much appreciated

Thanks

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You say the inlet manifold had a bow in it and it’s been reworked.

Have you checked the manifold is sitting correctly over the dowels in the head ? The manifold often hangs up on them looking like it’s seated but actually with a severe air leak underneath. Try spraying some brake cleaner underneath the manifold and see if the revs increase proving a leak. Mask the front of the carbs to ensure the mix doesn’t get sucked around to the front.

Mick Richards

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Hi again

Thanks for the replies,I have checked for air leak around manifold no change spraying brake cleaner,before having the manifold skimmed there was a change.

I have tried other plugs and even swapped the existing plugs around, nownot firing  on 1 and 3.did fire on 3 after putting another distributor in -felt chuffed that progress made-alas next day back to not firing on 1 and 3.      put the plug tester on 1 and 3 and sparking well and plugs are not wet. ???

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If you have compression and a spark it can only mean no fuel, especially as the plugs are coming out dry, but why only on 1 and 3 ?. If swapping the plugs makes no difference, and swapping the leads makes no difference, is the distributor cap tracking on the inside? Sometimes plugs will spark in fresh air but not under compression. Other than that is the cam timing right?

Ralph

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With all the swapping you have been doing with leads and dizzys, are the leads still in the right firing order or have 1 and 3 become accidentally swapped over ?

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18 minutes ago, RobH said:

With all the swapping you have been doing with leads and dizzys, are the leads still in the right firing order or have 1 and 3 become accidentally swapped over ?

I would go with Rob on that. It’s 1-3-4-2 so if you have 1-3 wrong that’s would explain it? Worth checking.

Kevin

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7 hours ago, boxofbits said:

I would go with Rob on that. It’s 1-3-4-2 so if you have 1-3 wrong that’s would explain it? Worth checking.

Kevin

Beat me to it.

Firing order is 1-3-4-2 and the distributor rotates anti-clockwise when viewed from above.  Ignition timing basic setting is 4 crankshaft degrees before top dead centre (TDC)  Confirm TDC marking of front pulley aligns to the timing cover pointer by observing position of no 1 piston.

Peter W

 

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Hi Again,thanks for the replies and the time that is involved

Double checked the firing order,1342-swapped plugs,no change.No sign of tracking in new cap.checked tdc marker-correct  double checked for leaks on manifold still not firing on tickover the 2 cylinders seem to come in at higher revs. Surely if cam timing was out it would affect all 4 cylinders? the tappets are rocking when at tdc.Monday I am going to check the valves are opening by same amount but on rebuild the cam looked fine

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7 minutes ago, mikespain835 said:

Hi Again,thanks for the replies and the time that is involved

Double checked the firing order,1342-swapped plugs,no change.No sign of tracking in new cap.checked tdc marker-correct  double checked for leaks on manifold still not firing on tickover the 2 cylinders seem to come in at higher revs. Surely if cam timing was out it would affect all 4 cylinders? the tappets are rocking when at tdc.Monday I am going to check the valves are opening by same amount but on rebuild the cam looked fine

I would question the lead’s there are some bad ones out there 

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If 2 fire and 2 don't then this is where your problem is .  As Neil says check the leads by swapping a bad one with one of the good ones. With the cap off when you turn over the engine can you see a spark at the 4 points  of the distributor cam ? if so then its cap/leads/plugs.

I have as reported in the past suffered several poor plugs [ NGK ] purchased from known companies and internet.

Roy

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The old-fashioned copper plug leads may produce a deal of interference  with radios and the like, but they seem to last for ever.  And cost little.

Guess which type of leads I use!

Ian Cornish

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6 hours ago, ntc said:

still not firing on tickover the 2 cylinders seem to come in at higher revs.

In that case it doesn't sound like an ignition fault.  Have you run the engine with the rocker cover off at idle to see whether everything is operating freely ?

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18 hours ago, mikespain835 said:

Hi Again,thanks for the replies and the time that is involved

Double checked the firing order,1342-swapped plugs,no change.No sign of tracking in new cap.checked tdc marker-correct  double checked for leaks on manifold still not firing on tickover the 2 cylinders seem to come in at higher revs. Surely if cam timing was out it would affect all 4 cylinders? the tappets are rocking when at tdc.Monday I am going to check the valves are opening by same amount but on rebuild the cam looked fine

From your earlier post you said that the misfiring cylinders plugs were dry when you took them out. On this post you say that they seem to "come in" on higher revs. That is sounding more like a fuel issue to me. Could the carbs be set very weak on tickover causing an intermittent misfire.

Ralph

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I don’t think any of us have mentioned rotor arm.

 Yes agree with the fueling comment but you say no spark in the lower rev range so still electrical for me.

Roy

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On 7/4/2021 at 6:57 PM, RobH said:

In that case it doesn't sound like an ignition fault.  Have you run the engine with the rocker cover off at idle to see whether everything is operating freely ?

You quoted something I did not say 

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??? I didn't quote you Neil.... it was Mike who said that in the post before yours.  I don't know why it got that header -  some forum bug. 

Edited by RobH
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I had a very similar problem with my tr6, swapped plugs leads and even a new dizzie, the problem seemed to change from one cylinder to another. It the end I bought six new plugs from a reliable source and problem solved. There appear to be some poor quality plugs on the market at the moment 

cheers

Alan

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I am still having problems,the plug leads are copper ,changed twice from different sources,swapped plugs around and still not firing on 1 and 3,new dizzy cap new rotor arm.Double checked(or triple) cam timing.Just seems very strange that it is not firing on the front inlet of each carb?almost that at idle it is not fuelling 1& 3.Above 1500/2000 revs as I say the engine evens out but as it comes below 1500 revs it is very noticeable that it goes onto 2 . I have checked that the balance pipe between carbs is not blocked going to do a vacuum test and maybe pull carbs to see if they were rebuilt correctly

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I'm new on this thread and did not read all:

you have no spark on this cylinders? 

If you have and they do not run, did you check the valve clearance.

And do the valves lift all the full lenght?

On a friends TR4A this was the issue - but it was running, more or less (more less).

Ciao, Marco

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I have checked the valve clearances again and checked that they open by the same amount.What I have done is check it with a colortune  I can see that 1 and 3 are sparking at tickover but no explosion,rev it and you can see the mixture ignite. also I put new plugs in and after just running it up to temperature took the plug out and it was black.engine starts first time?? getting more baffled as time goes on!

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Does your exhaust manifold have the 2 ports into the down pipe?  I have known on the 6 cylinder that you can fit the gasket so it covers the outlets a bit, as the bolt pattern is the same both ways.

John

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12 hours ago, John L said:

Does your exhaust manifold have the 2 ports into the down pipe?  I have known on the 6 cylinder that you can fit the gasket so it covers the outlets a bit, as the bolt pattern is the same both ways.

John

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

Stuart.

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