Increase Displacement

[daz]

My 1971 is a R50. Happily I was able to pick up an R75 engine made 8\1975. The R50 is fresher. Will the cylinders and top ends just switch out? Any hints or tips on this upcoming project? I do not have any carburetors yet.

[Bamboo812]

Yes they will swap out as long as the R75 is a 1975 model. Bigger spigots happened in 1976. The intake stubs for the R75/5 are different to accommodate the CV carbs and the R50 cam is milder than the R75/5 cam.

[daz]

Yes they will swap out as long as the R75 is a 1975 model. Bigger spigots happened in 1976. The intake stubs for the R75/5 are different to accommodate the CV carbs and the R50 cam is milder than the R75/5 cam.

Yes, according to the engine number it is August 1975. This is an engine where valve recession is a problem?

Do clutch parts interchange. How about starter motor?

[Kurt in S.A.]

Hopefully the cutoff truly begins with the first 1976 model as of September 1975. But given that this is August 1975, you never know if a new engine case was used on the assembly line. You wouldn't really know until you get in there.

All engines prior to the 1981 models are subject to valve recession. Beginning with 1981, the problem because valve face plastic deformation. Different mechanism, but still the same result.

Clutch parts should interchange. According to Snowbum's website, all starters were 8-toothed through most 1976 models. The '75 and '76 models were slightly more robust in terms of horsepower. Somewhere in the '76 models, they phased in the 9-tooth models.

[Bamboo812]

The 1976 and later cylinders with bigger spigots will have bigger diameter push rod tubes too.

[daz]

I have some loose exhaust nuts. I can check in the morning. So far, without any checking and measuring, it looks like I did OK with what I gave for the engine. It will meet my needs as well as giving me some spare parts. The engine came from a freshly wrecked \6 a few years ago. About 40K miles. Time will tell. It will be a fun project. Thanks.

[PAS]

Why not just do a complete engine change?

[Rob]

Why not just do a complete engine change?

from the OP: "The R50 is fresher."

[PAS]

Why not just do a complete engine change?

from the OP: "The R50 is fresher."

It wont be after its turned into a mix and match engine.

[daz]

Why not just do a complete engine change?

from the OP: "The R50 is fresher."

Yes, according to what I've been told the R50 is fresher. And it looks less used. But there will be a lot of measuring and inspection before any decisions are made. That's the sweet thing about getting the entire engine, I have lots of options. If I didn't want the spare parts I should have an R50 engine when I'm done. But I like spare parts.