Difference with spark plugs

[morrisminor]

Who can tell me the difference between NGK BP5HS and NGK B5HS, interested to know

[Reckless Rat]

The P stands for projected nose. The two plugs have the same heat range (5) but the BP5HS extends further into the combustion chamber. On an engine prone to oiling its plugs (and often when used on a late 37 head) it's not the better choice.

[morrisminor]

Thanks Reckless,  why are late 37 heads prone to sooty plugs ?

[Reckless Rat]

It's due to the position of the spark plug relative to the bore. On the late 37 head the plug hole is directly above the edge of the bore and if there's any wear then oil goes straight onto the plug nose.

[Bob Culver]

The difference in sensitivity cf the earlier heads is astonishing. At one stage with early head my car used a pint in 40 miles or less. After long descent cars behind vanished from view in the smoke screen but never missed a beat!  Later head using pint in 300 would sometimes miss once or twice opening out.

[JonE]

Can someone explain the difference here; if plug position makes later heads much more susceptible, then why would Bob have much more oil loss on an early head over a later one, please?

[Ian Williams]

The oil loss was nothing to do with the head Jon, Bob was driving a clapped out old car with an early head but it did not foul plugs, he was later driving a slightly less clapped out car with a later head but is did foul, I also suspect he had the wrong plugs in the later head and probably poor mixture as well. I have used Ruby head's extensively and with the right plug and correct mixture there no real issues in my experience, I do agree late heads are more prone to oiling plugs in a worn engine.

[Bob Culver]

Thankyou Ian

If a Seven using 1 pint per 300 miles of mostly distant flat out main road running is “clapped out”, how many are not?
I dunno if you know Wellington but my daily commute involved ascending Brooklyn hill (the southern extension of Willis St). At 35 in 3d the slightly modified RP swept past Morris 8s and Minors, Ford 8s and 10s and suchlike, very common at the time.
One impressed Ford 10 owner followed me home and wanted to buy it. It did not strike him as clapped out in full or part.
Recommended plugs were used but may not have been the optimum.

[Ian Williams]

I guess Bob it could be your terminology, a seven in good condition will not burn a pint of oil in 300 miles, (well mine don't) however some might leak that much oil if not put together well (again mine don't) If your car with late head was not burning oil but still fouling plugs you would have without doubt had one or more of the following issues; Incorrect timing, the wrong grade plugs fitted and or over rich mixture. Get these all these right and with good bores a Ruby head is completely trouble free in my experience.

[Rogerfrench]

Ian Williams, you might just be lucky, as well as a good assembler of A7 engines. The number of times that I've read about 37 heads fouling plugs, together with my own experiences and those of my father, lead me to suggest that the plug position is, shall we say, marginal.
What is true is that A7 blocks varied in quality, and some no doubt could be bored to be less oil-burning than others. What has always puzzled me is why Austins, having got it almost right with the unblown Ulster and Nippy heads, didn't keep the plug in a similar position on the 37.