1971 750 Engine Conundrum?

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RoadScholar

RoadScholar

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I am rebuilding an engine for a local customer; the motorcycle is a numbers matching example, 151167.

The left hand, drive side, engine case does not have the timed cam driven breather, nor a tapped/plugged hole there, but does have the breather that bolts to the rear of the case, that I would associate with '72 and '73 750 models.

Is this a factory possibility?

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I do not have the engine cases with me; I saw them, briefly, about 8 months ago, but I am pretty sure that the VIN does not have the 20M3S prefix, and I would think such a case would have the small hex sump plug, but can't say; I have asked the customer to make a visual check and will report the actual information when he sends it to me. I really appreciate the responses.

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As above responses although I suppose anything is possible as this is getting close to the end of the 15xxxx series. It could be a MkIV/V 750 case that was either re-stamped or was a new unmarked case that someone stamped. If you get inside the the later cases have the radial reinforcement webs around the main bearing area. Even if I have 151167 in the factory records copies I have it would not indicate the engine case type. Also check the three digit number at the bottom to see if both case sides and those matching. For example 967 stamped on both cases. If missing the number on the drive side might indicate a replacement.
 
The engine does have the 20M3s prefix, and a large sump plug, and the rear mounted breather.
 
RoadScholar said:
The engine does have the 20M3s prefix, and a large sump plug, and the rear mounted breather.
Click to expand...

I think @dynodave's head just exploded.

Another option is that the rear breather was machined after the fact.

As David said make sure the halves match. Is the large sump plug on the timing or primary side?
 
Bob Z. said:
The large sump plug is on the drive (left) side as well as the magnetic drain plug bolt.
Click to expand...

Well hells bells, can’t wait to see more pictures.

I’m voting that someone machined the back of the case for a breather.
 
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