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Old 09-23-2013, 07:06 AM   #1
tafouras OP
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R65 typ 247 1990 engine upgrade issue

Dear Advriders.

I came to purchase a 1990 BMW R65 Typ 247 with the 27hp version engine.

The bikes serial number is 6432418 R65. It uses two 26mm BING carbs with the codes

64/26/317 & 64/26/318, an 31/9 final drive and it runs fine in its low hp , but it is just not enough for me.

I am thinking of upgrading the bikes horsepower and I hear a lot of different things by Greek BMW "guru" mechanics. So I would very much appreciate your professional opinion on the choices I may have considering that I would be satisfied with just a few , lets say 10 more hp than the ones I already have.

1st choice is to upgrade the existing engine to 47 or 50 hp. What changes would I have to make in this case? I hear that I have to change the camshaft, the cylinder heads and the carbs to 32mm. Would that all be enough? What is your recommendation in this case and how much would the parts cost?

2nd choice is to give the engine a small amount of extra hp without making engine parts changing, just some improvements in functioning such as bigger carbs, better air breathing bigger exhaust tubes and .......whatever you would recommend. Do I have any luck this way , how many hp would I might gain with minor improvements and again what would you suggest if I finally choose this option?

Changing the whole engine with an used 50hp R65 or even to a R80 engine is not in my priorities for the moment due to cost and the leak of trust on buying a used engine with uncertain number of km in its life. But I do not completely reject that option for the future.

Looking forward for your answer.

Thank you forehand.

Best Regards
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Old 09-23-2013, 07:43 AM   #2
disston
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Sell the bike. It will never be what you want it to be. It is not even the 247 type engine. We let the R65 bikes on the Airhead forum and we mention all the time that the Airjheads are the 247 type engine but the R65 is not a 247 type engine.

To increase the HP from 27 to 47 is a doubling of HP, almost.

Save yourself the grief and expense. Buy a motorcycle that suits your wants and needs.
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Old 09-23-2013, 08:58 AM   #3
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Quote:
Originally Posted by disston View Post
It is not even the 247 type engine.

Save yourself the grief and expense. Buy a motorcycle that suits your wants and needs.
Agreed. On both points.

the engine is a type 248/1
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Old 09-23-2013, 09:49 AM   #4
guitstik
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For what it would cost you to upgrade the engine you could buy a bigger bike. Swapping a bigger engine into that frame is asking for trouble because it wasn't designed for it strength wise.
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Old 09-23-2013, 10:11 AM   #5
Prutser
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Quote:
Originally Posted by guitstik View Post
For what it would cost you to upgrade the engine you could buy a bigger bike. Swapping a bigger engine into that frame is asking for trouble because it wasn't designed for it strength wise.
Those bikes are the same as the R80 and the R100 mono's so they are designed for the bigger engine.
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Old 09-23-2013, 10:13 AM   #6
AliBaba
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Originally Posted by guitstik View Post
For what it would cost you to upgrade the engine you could buy a bigger bike. Swapping a bigger engine into that frame is asking for trouble because it wasn't designed for it strength wise.

Hmm, same frame was used for R65, R80 and R100: http://realoem.com/bmw/partxref.do?part=46511452025

Sadly I'm not sure of the differences between the 27hp version and the 50hp version.
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Old 09-23-2013, 10:14 AM   #7
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Quote:
Originally Posted by tafouras View Post
1st choice is to upgrade the existing engine to 47 or 50 hp. What changes would I have to make in this case? I hear that I have to change the camshaft, the cylinder heads and the carbs to 32mm. Would that all be enough? What is your recommendation in this case and how much would the parts cost?
That's entirely possible because the 27Hp model is just a detuned version of the normal R65. You have listed most of the differences, camshaft, valve sizes and carbs. In addition your 27HP engine will have a lower compression ratio. I'm not sure whether that is taken care of by the heads or the need for new pistons which could be costly. Your final drive should be OK as the same ratio was fitted to the 45Hp R65. If you did want to change it a new speedo with the correct ratio is also needed.

So possible but sounds expensive unless suitable 2nd hand parts can be easily sourced.
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Old 09-23-2013, 10:20 AM   #8
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The detuned 27hp R65 used 26mm bings while the normal ~50hp model used 32mm bings. I think I remember reading that the slides in the carbs were also limited in some way from fully openning. I've never seen them personally as they weren't sold here. I don't think the top end parts are in any way different.
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Airhead Wrangler screwed with this post 09-23-2013 at 10:28 AM
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Old 09-23-2013, 10:30 AM   #9
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Quote:
Originally Posted by Airhead Wrangler View Post
The detuned 27hp R65 used 26mm bings while the normal ~50hp model used 32mm bings. I think the slide in the carbs was also limited in some way from fully openning. I don't think the top end parts are in any way different.
The top end is different. Those heads are used on R45 models here in europe.
It is correct that the carb body's and the cam is different too.

The pistons used in the 27hp are not the same as the 50hp models.
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Old 09-23-2013, 10:33 AM   #10
guitstik
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I stand corrected, I missed or forgot that the OP's bike is a '90 model. The early R65's up to '85 used a lighter frame than all other airhead bikes so very little was comparable.
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Old 09-23-2013, 10:44 AM   #11
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R65's aren't airheads? First time I have ever heard that.
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Old 09-23-2013, 10:46 AM   #12
DaveBall
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It does not sound like you have an actual R65.

The R45 came in 2 flavours. Both are 450cc. A 35HP and a 27HP model. The 27HP model could be brought up to the 35HP version fairly easily. But to go any further requires major surgery, like new pistons and jugs, new carbs, different cam, etc. Cheaper to buy a good used 650 engine.
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Old 09-23-2013, 11:17 AM   #13
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Quote:
Originally Posted by Prutser View Post
The top end is different.
Oh. Nevermind then.
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Old 09-23-2013, 11:19 AM   #14
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Quote:
Originally Posted by DaveBall View Post
It does not sound like you have an actual R65.

The R45 came in 2 flavours. Both are 450cc. A 35HP and a 27HP model. The 27HP model could be brought up to the 35HP version fairly easily. But to go any further requires major surgery, like new pistons and jugs, new carbs, different cam, etc. Cheaper to buy a good used 650 engine.
They stopped production of the R45 in '85. From then on to meet the beginner rider requirements in germany, they sold detuned R65s making 27hp (the max allowed for a beginning rider in Germany at the time). From what I've read, all R65GSs were detuned to meet this standard except those sold to french police or the danish military. Other R65 models were sold to the public as both normal AND detuned versions.
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Old 09-23-2013, 12:10 PM   #15
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I rode an r65ls for 12 years and about 80k miles. Waste of time to try increasing power, and they aren't that reliable to start with. Your best bet it to get a used r80 motor.

You won't get bigger jugs on the r65 as the opening in the block needs to be larger. Some more info below, but considering my r12gs gets better mileage and has about 3x the power, and a reliable charging system I wouldn't go back.

http://www.chemie.unibas.ch/~holder/...POWER_INCREASE
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