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hooverbj's picture
VBMWMO #9255
Joined: 04/01/2017
Posts: 115

I took my 1966 R50/2 out to the hardware store today and was having difficulty starting it when I was leaving. Since I had new plugs and a spark plug wrench in my saddle bags, I thought I would pull them and do an inspection. I started with the right one and it seemed to unloosen easy enough but was more stiff than usual taking it the whole way out. Once it was out I noticed that the threads on it were twice the size. It looked like a big hunk of the head came with it. I concluded it must have been a repair that came undone? I put a new plug in the other side and screwed the whole assembly...spark plug and insert back on the other side. After several more kicks, it finally started. Its back in the garage now and I'm wondering if I am correct. Is this what I think it is? Someone repaired a stripped thread and installed a repair insert of some kind and I just screwed it back out? It did start and got me home. Is there some sealing compound I can put on the inset that would help it stay in place? Or do I need to take it to a machine shop and have it professional repaired?
Thanks in advance,
Brian Hoover
1966 R50/2
Cedar City, Utah

schrader7032's picture
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6844
The 1966 models (+ or -) were

The 1966 models (+ or -) were known as "butterheads". Something to do with the way the metal was treated/finished resulted in some softness to the heads. Duane talks about this as well as the plug inserts coming loose here about mid page:


We also had a discussion of sorts here:


I suspect your insert has worked loose. I don't know how the OEM inserts were installed but quite possibly they were like a large timesert or something. I would be inclined to not ride the bike much anymore but rather give them fixed professionally. Or maybe hunt down a new head, ideally one from the 1968 or 1969 era where there's no issue with the head material.


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

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