Pre-Ignition [Pinging] Question

[RobT]

Here is a question for the hive - kind of a follow-on from the TR8 spark plug discussion below.

I am getting some intermittant pinging on the TR - most often at low revs (<2,000RPM) under load/excelleration.

I have tried a bunch of things, including
- Retarding the ignition (currently 8 deg BTDC static)
- Enriching the mixture
- Adding a octane booster to the fuel.
None of which seem to have done the trick.

Should I try cooler spark plugs (could these being too hot be causing the pre-ignition?)

BTW, I have a "hot" cam and pretty high compression (10.5:1 or thereabouts)

Any other suggestions?

Thanks,

Rob.

 

[TR3driver]

Not likely to be plugs IMO, but worth a try.

Have you tried replacing wires & dist cap ? Almost sounds more like a cross-fire. If any parallel wires touch, try moving them apart (or making them cross at an angle).

Have you verified the advance curves ? Excess spark scatter ?

 

[RobT]

Thanks Randall.

Both the cap and wires are pretty new, and I have seperators on the wires to keep them apart (and looking neat), but will certianly try the old cap & leads and see if it makes a difference.

I have both the vacuume advance and retard on the distributor disconnected, and with a timing light, it looks like I am getting reasonable mechanical advance. The pinging seems to be most apparent at low revs so would doubt that's the issue.

What is the "excessive spark scatter" of which you speak? Any way to check for that.

Cheers,

Rob.

 

[TR3driver]

What is the "excessive spark scatter" of which you speak? Any way to check for that.

Sure, that's where the timing mark dances around under the timing light. If you've already checked the centrifugal advance through the rpm range, you would have noticed it (if it was there).

Sorry, can't think of anything else at the moment, except perhaps glowing combustion chamber deposits.

Well ... have you done anything to verify that the timing marks are accurate ? That's really grasping at straws, but I have seen engines where the front pulley has slipped and the marks no longer reflect reality.

 

[RobT]

What is the "excessive spark scatter" of which you speak? Any way to check for that.

Sure, that's where the timing mark dances around under the timing light. If you've already checked the centrifugal advance through the rpm range, you would have noticed it (if it was there).

I HAVE noticed such an effect - just attributed to the timing light. What is the cause/cure? (BTW I have a Crane electronic ignition, with optical pick-up in the dizzy).

Sorry, can't think of anything else at the moment, except perhaps glowing combustion chamber deposits.

Wondered that - but the solution would be to pull the head - yuck! Doubt an "italian tune-up" would do it.

Well ... have you done anything to verify that the timing marks are accurate ? That's really grasping at straws, but I have seen engines where the front pulley has slipped and the marks no longer reflect reality.

Good point! I will check that - using a gauge in cylinder #1.

Thanks again.

Rob.

 

[AltaKnight]

That is pretty high compression ratio, with that high CR, I think you're always going to struggle to stop the pinging with heavy load+low rpm.
So the answer is....use high octane fuel and drive it in a lower gear with higher revs!

 

[tom628]

Just as a long shot, if you're running a 180 deg. thermostat you might try switching to a 160. Head should run a little cooler. I don't think my CR is that high, but flushing the cooling system and using the 160 t.stat eliminated the pinging for me.

Tom

 

[70herald]

Here is a question for the hive - kind of a follow-on from the TR8 spark plug discussion below.

I am getting some intermittant pinging on the TR - most often at low revs (<2,000RPM) under load/excelleration.

BTW, I have a "hot" cam and pretty high compression (10.5:1 or thereabouts)

Any other suggestions?

Thanks,

Rob.

Ouch, 10.5:1 is pretty high for normal gas, and full throttle a low RPMs will give the engine a good full dose of air, which will create a high dynamic compression ratio. (the 10.5:1 is static CR and there is a difference!)

Try both a lower temp spark plug and a lower temp thermostat. You will have to check to see if the spark plugs stay clean. If they foul up as a result of the lower temperature they probably aren't the cause of your problem in any case.

 

[TR3driver]

Sure, that's where the timing mark dances around under the timing light. If you've already checked the centrifugal advance through the rpm range, you would have noticed it (if it was there).

I HAVE noticed such an effect - just attributed to the timing light. What is the cause/cure? (BTW I have a Crane electronic ignition, with optical pick-up in the dizzy).

Generally it's wear inside the distributor. The Crane reduces the scatter due to wear, but does not eliminate it. Could also be excess end float in the camshaft or distributor drive gear; possibly even a broken timing chain tensioner.

Also check that the rotor is not hitting the pickup. Took me a long time to realize my rotor had a "counterweight" that was smacking the pickup housing every rotation.

The Crane also introduces another possibility, that the phasing is off enough that the spark sometimes jumps to the wrong cylinder. Try making some small changes in it (by moving the pickup on it's slots, relative to the point plate), then reset the timing and see what effect it has on the problem. I wound up having to cut the bracket to get the phasing right. With only a 4-banger, the sparks going to the wrong cylinders were just wasted; but with an 8, they might well set off the mixture during the compression stroke.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Doubt an "italian tune-up" would do it.[/QUOTE]Still worth a try, IMO. Besides, it's fun !

You mentioned retarding the spark but said you were only at 8 BTDC. As an experiment, try TDC.

Also, all octane improvers are not created equal. When I was running around 11:1, the only ones that did anything at all for me were the ones with MMT in them. (Generally labeled "racing formula" or "not street legal"; tho AFAIK there is currently no legal restriction on MMT. Check the fine print for the MMT warning.) Had to start out using quite a lot of it, but after a few tankfuls, I found I could get by with less. It's a balancing act, though, because the stuff will foul your plugs (with a funky pink or orange color).
https://www.classictruckshop.com/clubs/earlyburbs/projects/spark/plugs.htm

 

[RobT]

Thanks Randall and others for the great suggestions!

I will pull the dizzy and check for slop and make sure the rotor is not fouling anywhere. Also I'll pop in some cooler plugs and see how that goes.

I was speaking to my brother last night (another Triumph nut) and he suggested it might just be crappy modern fuel. Apparently modern "higher octane" fuel degrades pretty quickly - in a matter of weeks - to lower octane. So if you are not driving the car every day, don't necessarily fill the tank all the way each time, and just have as much as you will use over the next few weeks so as to keep it fresh.

I am using Lucas octane booster, which has the MMT warning and is "NOT STREET LEGAL" (so is it legal on roads and highways?), but might also up the dosage of that.

So back to the tinkering! Thanks again guys and I'll report if I find anything.

Rob.

 

[TR3driver]

I am using Lucas octane booster, which has the MMT warning and is "NOT STREET LEGAL" (so is it legal on roads and highways

AFAIK, Yes. The EPA had banned it for awhile, but was eventually forced to reverse the ruling when no evidence that it harmed catalytic converters turned up. And unlike lead, there doesn't seem to be any indication that low levels of manganese are harmful (tho of course too much of anything is bad for you).

 

[mailbox]

I was speaking to my brother last night (another Triumph nut) and he suggested it might just be crappy modern fuel. Apparently modern "higher octane" fuel degrades pretty quickly - in a matter of weeks - to lower octane. So if you are not driving the car every day, don't necessarily fill the tank all the way each time, and just have as much as you will use over the next few weeks so as to keep it fresh.

It's my understanding ethanol is used as an octane booster in a lot of gasolines today. If it sets in a tank too long it will evaporate and leave you with lower octane fuel.

 

[DNK]

Then the fuel in my 6 is 16 octane

 

[RobT]

So following up with the results to the suggested changes:

I swapped out the plugs (cooler NGK's) and thermostat (165 deg). These changes certainlly seem to help (did both at the same time so not sure which had the most impact). I can still get it to ping a little - but only at low revs, under load. I have to work at it.

So more revs is clearly the answer to that. Otherwise the car is going great. Best its ever run I think, and the various suspension mods/refreshes and brake uprates make it a blast to drive.

Rob.

 

[MichaelG]

Rob,

One way to answer the fuel question might be to try some 100 octane AvGas. You could get some at Minuteman Airfield in Stow. Not recommending that any of us switch to leaded fuel, but a few gallons to test the octane theory and see if it stops the pinging temporarily might be interesting.

Listers, is there any downside to trying this? I've often thought of trying it just to see if there was any noticeable change in performance

Cheers

Mike Godley
65 TR4A
Acton,MA

 

[myspitfire]

Sure!A bigger explosion=CRACKED PISTON
:lol:

 

[RobT]

Sure!A bigger explosion=CRACKED PISTON
:lol:

Wouldn't think so actually. These engines were designed for the higher octane UK and European fuels. And I bet the race guy's run them at higher than 100 octane.

Mike - Thanks for the suggestion. I'll get out there for breakfast at the Airfield Cafe and gas up the car at the same time! So you are in Acton - right next door. What colour TR and I'll look out for you on the road (some of my favourite short drives are through Acton - Nagog Hill Rd, Strawberry Hill Rd etc. Really nice this time of year.

Cheers,

Rob.

 

[swift6]

Sure!A bigger explosion=CRACKED PISTON
:lol:

Wouldn't think so actually. These engines were designed for the higher octane UK and European fuels. And I bet the race guy's run them at higher than 100 octane.

Higher octane fuel isn't more explosive or more powerful. It burns with a slower flame front and can therefore tolerate higher compression which is where the power is made. Putting 100 octane fuel in won't hurt anything but it might not help anything either. Other than making your exhaust smell a little more racy. Its counterintuitive but the lower octane fuels are more dangerous than the higher octane fuels as they are more likely to generate pre-igniton combustion which will hurt your engine.

The European fuels are generally not that much higher in octane either. They are rated by a different system. Their octane ratings are based on a single method, known as the "Research Octane Number" (RON). While our octane ratings are based on the average of two different methods, the RON and the MON (Motor Octane Number). Which is why when you go to a US fuel pump you see a sticker that shows "R+M/2" (RON+MON/2). Our method usually results in a octane rating 4-5 points lower than just the RON number. Their 98 octane would be the same as our 93 octane, their 95 would be our 91 etc... When they offer 100 octane fuels, we don't generally have the equivalent offered over here though. Lastly, the fuels that most of these cars were made for were also leaded fuel with higher octanes. So the recomended gasolines in the owners manuals are not as accurate as they once used to be.

 

[tom628]

Rob: 100LL avgas should be OK in the TR engine for a tank or two. I wouldn't run it long term, however, because of the likelihood of lead fouling of the plugs, and possibly the valves.
100Low Lead is actually quite high in lead, and only "low" in relation to the formulation it replaced. It has 4X the lead content of the 87 oct. avgas, which is now almost impossible to find.

Tom
76 TR6
47 Luscombe 8E

 

[myspitfire]

Spend your money take your chances my friends!