Which spark plugs for 202?

**p38arover** · 21st May 2012, 02:01 PM

I want to replace the plugs in the 202-engined IIA.

The plugs I removed were Bosch H9BC which have a short thread. I've not looked into a 202 plug hole before and it seems to me that this plug is too short, thread-wise.

This the hole:

I've been given some Champion BN7Y plugs which have a 3/4" long thread and some BL-9Y which look the same as the Bosch, i.e., short thread.

I found this pic and annotation on the 'net which indicates I should be using the long readc plugs. I just want confirmation.

Some Heads have no Spark Plug Thread for the first 3/8". In this case 202 Plugs won't fit because there is no Thread for them. A 3/4" Reach, Tapered Seat, Projected Nose Plug similar to Bosch HR7DCY should be used. Photo by TUFFVB.

**BigJon** · 21st May 2012, 02:07 PM

My NGK book shows BP5FS or BP5ES depending on thread length and seat type. It seems that 202s could take either depending on exactly which engine it is.

**p38arover** · 21st May 2012, 02:16 PM

Thanks Jon.

The Bosch H9BC doesn't appear in their catalogue but they show the 202 using the HR9BC (which I assume to be a resistor plug)

**p38arover** · 21st May 2012, 03:11 PM

I'm trying to work out if it uses a washer or conical seal. Different spark plug manufacturers list one of the other.

Here's another pic. To tell the truth, it's hard to be sure. It looks like the outer larger hole has a conical taper and the inner is flat.

I don't want a plug that's through too far as the threads may get carboned up.

Running a bent scriber point over the threads seems to indicate there is a long thread there, not short. I wish I could get my eye down there. Maybe my crappy inspection camera will work.

**p38arover** · 21st May 2012, 03:47 PM

Ahh, it looks like the plugs might be the short thread. I got the scriber again and ran it over the threads and counted them.

The video inspection camera was useless.

**bee utey** · 21st May 2012, 03:56 PM

Red 173/202's ran short reach taper seat plugs. Blue and black 6 cyl motors ran long reach plugs. The larger taper in your pics has marks from the plug socket. The innermost taper is the one that seals. HR9BC should be correct for petrol operation. H9BC (non resistor) is a discontinued plug.

**p38arover** · 21st May 2012, 04:14 PM

Excellent. Thanks gentlemen.

Davehoos · 21st May 2012, 06:44 PM

if the engine rpm is more than 3K and a bit on the road try a colder heat range.the older heads with BP5ES we run BP6ES[copper core]

the black engines tended to run best with the A/Cdelco plugs-lot of people tell me they are bosch but the super bosch sold in parts shops wasnt as good.

very common to melt plugs on hyway runs.
or preignition when switching off.

the engines tended to have retarded timing so than ran a bit hotter-when you tunned them to run properly you had to watch[listen] for pinking.

**justinc** · 21st May 2012, 06:46 PM

Originally Posted by Davehoos

if the engine rpm is more than 3K and a bit on the road try a colder heat range.the older heads with BP5ES we run BP6ES[copper core]

the black engines tended to run best with the A/Cdelco plugs-lot of people tell me they are bosch but the super bosch sold in parts shops wasnt as good.

very common to melt plugs on hyway runs.
or preignition when switching off.

the engines tended to have retarded timing so than ran a bit hotter-when you tunned them to run properly you had to watch[listen] for pinking.

That black EST engine was an abomination

JC

**p38arover** · 21st May 2012, 10:03 PM

Originally Posted by Davehoos

if the engine rpm is more than 3K and a bit on the road try a colder heat range.the older heads with BP5ES we run BP6ES[copper core]

the black engines tended to run best with the A/Cdelco plugs-lot of people tell me they are bosch but the super bosch sold in parts shops wasnt as good.

very common to melt plugs on hyway runs.
or preignition when switching off.

the engines tended to have retarded timing so than ran a bit hotter-when you tunned them to run properly you had to watch[listen] for pinking.

The IIA is going to a property shortly and won't be used on road. The new owner came the other day and got it going.

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