9 replies [Last post]
sblaylock
sblaylock's picture
 Offline
VBMWMO #8384
Joined: 07/22/2010
Posts: 106

I'm looking for a couple of spark plugs for my R62 that would have been on the bike back then. Would they have been Bosch plugs from the 20's or a different brand. I'm looking for something to put in the bike for shows.

Thanks,
Scott.

Darryl.Richman
Darryl.Richman's picture
 Offline
VBMWMO #6285
Surf City, USA (Santa Cruz, CA)
Joined: 10/27/2006
Posts: 2183
Certainly Bosch made plugs

Certainly Bosch made plugs then, but I'm not sure what else would have been available.

Your R62 would have been set up for 18mm plugs. These are still available from Bosch, at leastin Germany. The M7AC or M8AC plugs will be what you need. I'm running M7ACs in my R52, which I bought in 2006 in Germany, at a Bosch dealer -- he had them in stock and they were just a couple euros each! But they do look like any other Bosch plug today, white insulator with green rings.

__________________

VBMWMO Webmaster,--Darryl Richman
http://darryl.crafty-fox.com

sblaylock
sblaylock's picture
 Offline
VBMWMO #8384
Joined: 07/22/2010
Posts: 106
Thanks Darryl. What's the

Thanks Darryl. What's the difference between the M7 and the M8. The data I fouind on the M8 was "18MM THREADED
Fits: UNIVERSAL > 750CC/1200 SIDE VALVE; 36-47 KNUCKLE MODELS(NU)". Are you running the M7 version in your R52 as it's not a 750?

I have Champions in it right now - don't know the model, but in the two times around the block they worked fine. Still getting the bike sorted.

Scott.

Ian R11
Ian R11's picture
 Offline
VBMWMO #8148
Yorkshire uk
Joined: 10/22/2011
Posts: 195
Pictures showing some plugs

Pictures showing some plugs that were in my R62, unused for 60 years. I don't know if they would be original then as it would have been 20+ years old when running these.
I believe I can make out markings r272e on the shoulder. They don't cross reference with anything from my plug supplier in UK. They carry D7AC Bosch plugs, the same as Dreher supplied me. Check their site www.gsparkplug.com They carry some older type plugs with multi electrodes.

  • img_0274.jpg
  • img_0275.jpg
Darryl.Richman
Darryl.Richman's picture
 Offline
VBMWMO #6285
Surf City, USA (Santa Cruz, CA)
Joined: 10/27/2006
Posts: 2183
That's a great site! From

That's a great site! From what I can see, the D series plugs have a tapered seat, rather than the flat collar, above the threads. The M7ACs that I'm using look like this:

__________________

VBMWMO Webmaster,--Darryl Richman
http://darryl.crafty-fox.com

sblaylock
sblaylock's picture
 Offline
VBMWMO #8384
Joined: 07/22/2010
Posts: 106
So, the M7s are good in the

So, the M7s are good in the R62? I was wondering what the difference was between the M7 and the M8.

That is a great site and resource for plugs.

Scott.

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6327
I found Bosch plug M8AC0 on

I found Bosch plug M8AC0 on http://www.clubplug.net. What does the zero at the end mean?

If the plug numbering was the same back then, the number indicates heat range, with the higher number being hotter. M indicates it's 18mm x 1.5 threads. Other good stuff to break down the number here:

http://www.retrospeed.org/documentacion/bosch_spark_plug_guide_official.pdf

__________________

Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

sblaylock
sblaylock's picture
 Offline
VBMWMO #8384
Joined: 07/22/2010
Posts: 106
Hotter Plug for Air Cooled Engines?

Kurt, Thanks for the links. I'll probably order a set of M7s and a set of M8s and see which one works best with my bike, but for our air cooled engines should we be running a hotter plug.

From what I've read a hot plug has a longer insulator nose, which exposes more surface area to the combustion gases. This is to ensure the temperature at the insulator nose stays sufficiently high to burn off carbon and oil deposits. A cold plug is the opposite. The shorter insulator nose minimises exposure to combustion gases for faster transfer of heat to the cylinder. With an air cooled engine I'm not sure I want to transfer more heat to the cylinder.

Scott.

Bruce Frey
Bruce Frey's picture
 Offline
VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
The original Bosch spark plug

The original Bosch spark plug designation for the R62 and other sidevalve BMW of that era is W (14mm) or M (18mm) 175T1. These are equivalent to W or M7AC. OHV engines usually use a colder plug, which would typically have heat ranges of 200 (current heat range 6) or 225 (current heat range 5). Higher numbers used to be colder.

My sidevalves (R12 and R6) are usually happy with modern Bosch heat ranges of 7 or 8.

I am attaching a sheet from Bosch explaining (in German) their old legend and a Bosch poster with some REALLY hot plugs.

I may have some old Bosch plugs with the old style legends if anyone is interested.

Bruce

PreviewAttachmentSize
c3000fax.tif45.64 KB
  • bosch_6_1024x768.jpg
sblaylock
sblaylock's picture
 Offline
VBMWMO #8384
Joined: 07/22/2010
Posts: 106
Vintage Plugs

Bruce Frey wrote:

The original Bosch spark plug designation for the R62 and other sidevalve BMW of that era is W (14mm) or M (18mm) 175T1. These are equivalent to W or M7AC. OHV engines usually use a colder plug, which would typically have heat ranges of 200 (current heat range 6) or 225 (current heat range 5). Higher numbers used to be colder.

My sidevalves (R12 and R6) are usually happy with modern Bosch heat ranges of 7 or 8.

I am attaching a sheet from Bosch explaining (in German) their old legend and a Bosch poster with some REALLY hot plugs.

I may have some old Bosch plugs with the old style legends if anyone is interested.

Bruce

Hi Bruce,

Thanks for the info on the plugs. I've ordered 4 M7ACs as they seem to be the plug of choice for the R62/R52. Do you run the same plug in your R12? The only difference I can see between the M7AC and the M175T1 is the M7A(C) - Copper electrode, M175T1 - Nickel electrode.

I would be interested in a set of the vintage plugs if you have them available. Would they be appropriate for the R62?

Thanks,
Scott

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.