TR4 Spark Plugs

[Adam Blackaby]

Why is Sunday afternoon the time for playing with the TR?

Latest issue, decided today to undertake plugs, leads and coil change.

As per Moss catalogue I had a set of NGK BP6HS plugs to hand. But, taking old ones out I discovered that they were 5HS versions. Looked on the web but I couldn't find any clear explanation of difference. (The old spare plugs in the boot were 6HS's)

Unfortunately its p.....ng with rain so I can't take the car out for a test but it starts and revs fine with the new plugs in.

Is there any difference between the two?

Thanks in advance

[RobH]

That is the heat range Adam - i.e. how well the plug gets rid of heat.  In the NGK system a lower number is a 'hotter' plug so your 5HS is a bit hotter plug than the 6HS.  I think it's usual to use the 6 on a standard TR 4-pot engine. 

https://www.ngk.com/what-is-a-spark-plugs-heat-range-2

 

 

[ctc77965o]

The hotter plug, (5HS) helps prevent fouling of plugs due to rich mixture (too much choke for instance), but theres more chance they cause preignition during extended hi-speed runs... the 6HS is less likely to cause pre-ignition but more likely to foul... if it runs nice with 5s, stick with 5s

[Lebro]

I ran with 5's up to my recent engine rebuild as the plugs were prone to fouling. I am now on 6's.

Bob.

[Hamish]

2 hours ago, Lebro said:

I ran with 5's up to my recent engine rebuild as the plugs were prone to fouling. I am now on 6's.

Bob.

i'm with bob - i also use 6's

[BlueTR3A-5EKT]

Adam.

As stated. BP 6 HS is the most common figment. BP 5 ES get fitted if the engine is a bit of an oil burner and prone to fouling.   

Peter W

PS was your green Bristol a 400 or 401? PJT and I are discussing it.  I say 400 as it had lop sided SU carbs.

 

[Adam Blackaby]

Thanks Guy's.

As expected, you had the answers.

I'll see how it goes on the new plugs and revert to 5HS's if needed. I'm sure they they were fitted for a reason, previous owner had the car maintained by Glen at Protek.