Hello there I am new to this forum,but have owned and worked on a number of boxer twins. Currently repairing and modifying an R80 RT for a friend.
My question is ; can the rear end of an R45- ie sub frame, swinging arm,suspension and wheel , be fitted to the R80 front main frame? The R80's is damaged and have been offered this if it will fit without too much trouble..
Frame adaption
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Rob Frankham
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Re: Frame adaption
We need to know the year of both of the machines to make a definitive comment.
In any case, you should be aware that using the swing arm and sub frame will reduce the wheelbase of the machine by around 2 inches and this may have an adverse effect on handling, especially on a machine fitted with the 'RT' fairing.
Rob
In any case, you should be aware that using the swing arm and sub frame will reduce the wheelbase of the machine by around 2 inches and this may have an adverse effect on handling, especially on a machine fitted with the 'RT' fairing.
Rob
Re: Frame adaption
According to the specifications a 78 -80 R45 has a 10mm shorter wheelbase and both the swinging arm and subframe are different part no's from the 81-85 R45.
That would imply that the later model swinging arm may be 10mm longer. It seems like a lot of fuss to change the part no for 10mm but I can't think of any other difference between them.
As Rob said, either type of R45 swinging arm would be substantially shorter than the original R80 and it's worth remembering that historically the original /5 models which had a similarly short wheelbase to the R45 then had 2" added to improve stability.
Neither of the R45's are unstable but you can't read anything in to that based on wheel base alone because the steering geometry is different to an R80.
Wheelbase specs
Early /5 1385 mm
78-80 R45 1390 mm
81 -85 R45 1400 mm
R80/7 1466 mm
That would imply that the later model swinging arm may be 10mm longer. It seems like a lot of fuss to change the part no for 10mm but I can't think of any other difference between them.
As Rob said, either type of R45 swinging arm would be substantially shorter than the original R80 and it's worth remembering that historically the original /5 models which had a similarly short wheelbase to the R45 then had 2" added to improve stability.
Neither of the R45's are unstable but you can't read anything in to that based on wheel base alone because the steering geometry is different to an R80.
Wheelbase specs
Early /5 1385 mm
78-80 R45 1390 mm
81 -85 R45 1400 mm
R80/7 1466 mm
barry
Cheshire
England
Cheshire
England
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Rob Frankham
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- Joined: Thu Aug 26, 2010 2:11 pm
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Re: Frame adaption
Thinking a little more about this...
Not knowing where you are, it's difficult to be specific but of all the used parts you can get for an airhead, the rear subframe is probably among the cheapest and easiest to source. A used part dealer I know told me that he throws most of them in the skip... they are seldom needed and not worth the storage. If you contact the used parts dealers in your part of the world, it's likely that you will source the one to match your machine and avoid all of the issues with potential mismatches.
Rob
Not knowing where you are, it's difficult to be specific but of all the used parts you can get for an airhead, the rear subframe is probably among the cheapest and easiest to source. A used part dealer I know told me that he throws most of them in the skip... they are seldom needed and not worth the storage. If you contact the used parts dealers in your part of the world, it's likely that you will source the one to match your machine and avoid all of the issues with potential mismatches.
Rob
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Colincondor
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- Joined: Mon May 26, 2025 3:09 pm
Re: Frame adaption
Hi to you all and thanks for the info. As it seems to not be a good idea due to altering the steering geometry we will look to finding the proper parts. I am up in the west midlands in uk and there are a few breakers around . Also the fairing has been removed. Thanks again
Colin Condor.
Colin Condor.
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Rob Frankham
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- Joined: Thu Aug 26, 2010 2:11 pm
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Re: Frame adaption
Motorworks and Sherlocks do used parts and are probably the best known suppliers. There are others. Probably the best source is Ebay.Colincondor wrote: ↑Wed May 28, 2025 4:41 pm Hi to you all and thanks for the info. As it seems to not be a good idea due to altering the steering geometry we will look to finding the proper parts. I am up in the west midlands in uk and there are a few breakers around . Also the fairing has been removed. Thanks again
Colin Condor.
Be aware, though, that there were several changes to the rear subframe over the years, both large and small which will effect the fitting. In particular, a 'RT built after 1984 (Model year '85 and beyond) will have a very different subframe to an earlier 'RT. That being said, in most cases a subframe from any model (except 'GS off road based models and R45/R65 models) of the same year will be identical. Could be more specific if I knew the year of the machine you're working on... the history of the airhead series between 1969 and 1995 is incredibly convoluted.
Rob