1978 R100/7 engine in R80/7 frame

[tomcoates93]

Morning all,

Newbie here so apologies if this one has been answered before.

I have a 1978 R80/7 which has had an engine failure and the mechanic has said it's not worth repairing and that it would be easier to look for a second hand engine to replace it with. I'm struggling to find a direct replacement but can find an 1978 R100/7 engine on ebay that is the same year. Does anyone know how straightforward the swap would be and could you tell me of anything that I would need to consider or allow for please?

I've done a bit of research and I seem to think it would be ok but it's worth asking the question!

Thank you,

Tom

 

[KMD]

@mikeyboy is your man for this one.

 

[DrFarkoff]

Morning all,

Newbie here so apologies if this one has been answered before.

I have a 1978 R80/7 which has had an engine failure and the mechanic has said it's not worth repairing and that it would be easier to look for a second hand engine to replace it with. I'm struggling to find a direct replacement but can find an 1978 R100/7 engine on ebay that is the same year. Does anyone know how straightforward the swap would be and could you tell me of anything that I would need to consider or allow for please?

I've done a bit of research and I seem to think it would be ok but it's worth asking the question!

Thank you,

Tom

Yeah they are pretty much the same engine

The /7 is Usually a Heavy flywheel engine

"But" may already have been changed They will usually have the engine number stamped on the block beside the oil filler / Dipstick

Fire it on here and whoever is up first will check production date

What "failed" on your 800 engine ?? You might be able to just use the block and fit your Pistons and heads and barrels if you want to keep it 800 cc

 

[JJH]

It would be interesting to know what failed. There’s a lot of expertise on here. JJH not me

 

[mikeyboy]

The engine will fit in the frame,no problem.
First things to check/ compare.
Both motors heavy flywheel?
Both motors have points?(the 100 could have points in bean can,depending on when exactly it was built)
Both motors have 38mm exhaust ports (100rs of that era could have 40 mm ports)
The 100 motor should have 40mm bings,the 80 has 32mm.
78/79 bikes saw a few changes so you need to check exactly what you might be buying.
As asked above,what’s wrong with the engine?
It’s best to keep matching numbers if it’s viable.
The replacement might be no better or worse than the existing one,after all it’s 45 years old,
I’ve never yet taken an engine apart from a bike of this age that was perfect,most will need valve gear work which can get pricey.

 

[mikeyboy]

As a by the by,
Do you want to sell it as is

 

[tomcoates93]

Wow - some quick informative replies, thanks.

I'll have to conversation with the mechanic about it and get back to you but he didn't seem to think much was salvageable. The bike was made in to a scrambler / custom by someone and I bought it off ebay back in the summer. I always wanted to learn and take on a project myself but never seemed to have the time, especially with a young son so I ended up buying one already done. After debating it for several years, I thought it would be better to have one that I can ride! The problem is/was, you don't know what the other person has done and it looks like I might've fell on the wrong side of that.

I love the bike though, it has heaps of character and it will definitely be going back on the road.

 

[Wrigsby1]

Wow - some quick informative replies, thanks.

I'll have to conversation with the mechanic about it and get back to you but he didn't seem to think much was salvageable. The bike was made in to a scrambler / custom by someone and I bought it off ebay back in the summer. I always wanted to learn and take on a project myself but never seemed to have the time, especially with a young son so I ended up buying one already done. After debating it for several years, I thought it would be better to have one that I can ride! The problem is/was, you don't know what the other person has done and it looks like I might've fell on the wrong side of that.

I love the bike though, it has heaps of character and it will definitely be going back on the road.

Try and get a few details for those that know on here... Like getting a 2nd opinion before they take yer leg off...