Dellorto PHM38 BD 60/5

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r75boxer
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Dellorto PHM38 BD 60/5

Postby r75boxer » Wed May 15, 2019 11:25 pm

Hello all. I'm looking for information on the carbs that came with my '82 R100RS. The fellow I purchased the bike from (a BMW mechanic) told me that the 38mm Dellortos require a 60/5 slide. The carbs came with 60/2 slides. Can I run these or do I need to find the correct ones? If the correct ones HAVE to be used, I have been unable to find 60/5 slides as they are no longer made but new ones with some modification can be had.

Kevin
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Re: Dellorto PHM38 BD 60/5

Postby Mike D » Thu May 16, 2019 12:38 am

Your model was never sold with Dellortos carbs, but Bing carbs. Looking at http://www.bmbikes.co.uk/specpages/R100RS.htm shows 2 constant depression carburettors, Bing 94/40/105 - 94/40/106.

Mike

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r75boxer
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Re: Dellorto PHM38 BD 60/5

Postby r75boxer » Thu May 16, 2019 1:24 am

I guess I knew that but this bike is somewhat modified with a beefed up frame, dual spark and ported etc..
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Re: Dellorto PHM38 BD 60/5

Postby Mjolinor » Thu May 16, 2019 6:21 am

It's hard to imagine anything that needs beefing up on an Airhead frame, it's proper, German, "built like a tank" engineering. :)

Your question can really only be answered by the guy that did the mods to the engine or by investigation, trial and error.

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Re: Dellorto PHM38 BD 60/5

Postby Rob Frankhamr » Thu May 16, 2019 10:01 am

I can't answer the question. The substitution of Dell Orto carbs seems a lot more common in North America than in the UK. It might be an idea to post the question on one (or more) of the US forums. I found the Boxerworks forum https://forum.boxerworks.com a friendly and useful resource.

Rob

Edit...

A quick bit of research confirms that the Dell Orto PHM38 is the carb type fitted as standard to the R90s (the only airhead fitted as standard with Dell Orto carbs. I would suspect that the slides supplied for that use would work. I am also reading that there are two types of slide, one for use with carbs with a metal top and the other for use with later carbs that have a plastic top. Don't know if that is of any use.

One final point. The designation BD indicates a right hand carb, the left carb should be designated BS.

Rob
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Re: Dellorto PHM38 BD 60/5

Postby Rob Frankhamr » Thu May 16, 2019 10:42 am

It's hard to imagine anything that needs beefing up on an Airhead frame, it's proper, German, "built like a tank" engineering. :)

Your question can really only be answered by the guy that did the mods to the engine or by investigation, trial and error.


You've obviously never heard of the nickname 'Gummikuh'(German Lit. Rubber cow)... There has always been a persistent myth that the airhead frame is subject to flexing. I don't think there's any real truth to it, especially in comparison to other frames being made in the same era although it may have some slight truth when measured against thoroughly modern cast alloy units. My personal thinking is that, as a story, it is fueled by the unusually compliant suspension that is a feature of BMW's and reinforced by BMWs own advice that the frame isn't suitable for fitment of a sidecar.

Whether there's any truth behind it or not, the story has spawned a micto industry in the manufacture of frame braces, supposedly intended to cure the flexibility but which, when looked at with an objective eye, only really have the effect of making engine access more difficult.

In my (not so) humble opinion, unless you intend to campaign your bike in serious competition, any extra frame bracing is nothing more than expensive and unnecessary eye candy and, if you seriously want to make the frame more rigid, then you need to do a lot more work than bolting (or welding) on a couple of bits of bent tubing. (I'm sure there are others who will disagree... :twisted: )

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Re: Dellorto PHM38 BD 60/5

Postby Mjolinor » Thu May 16, 2019 11:37 am

Aha, not frame flex.

https://translate.google.com/translate? ... rev=search

I like that expression and yes, never heard of it. Clearly a rare thing, a German with a sense of humour. :)
Last edited by Mjolinor on Thu May 16, 2019 11:43 am, edited 1 time in total.

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Re: Dellorto PHM38 BD 60/5

Postby windmill john » Thu May 16, 2019 11:38 am

Off topic slightly, ahem....

I love the frame on the WW2 R75. Each section was bolted to the next. so whatever happened to the bike, you just unbolted a length and replaced.
I'm sure it didn't help stop flex (back on topic) having so many parts to the frame but wow, what a simple solution to stripping a bike.


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Re: Dellorto PHM38 BD 60/5

Postby r75boxer » Thu May 16, 2019 1:36 pm

Thanks to all for your comments. I will take a few photos of the frame bracing today. I think you'll agree that it is factory or the best damn work you've ever seen. The original owner cannot be contacted but the fellow that I purchased the bike from is from Germany, and was trained as a BMW mechanic in Germany. He recalls having seen this mod made by BMW at the factory.

So, does anyone have any leads on where to source 60/5 slides?

Kevin
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'73 R75/5
'58 R26
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Re: Dellorto PHM38 BD 60/5

Postby Rob H » Thu May 16, 2019 1:49 pm

Dellorto carb parts can be obtained from Eurocarb in Uk, though generally not cheap.

https://www.dellorto.co.uk/

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Re: Dellorto PHM38 BD 60/5

Postby nmag » Thu May 16, 2019 3:16 pm

Dellorto UK are quite expensive. I have PHF's on the Laverda and get my parts from some of the scooter (Vespa and Lambretta) shops, which are usually about half the price. Compared to the Bings, the float height is critical on the Dellortos and best way to set it is with the carb on the worktop. Also those pumper carbs can be sore on the petrol consumption.

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Re: Dellorto PHM38 BD 60/5

Postby r75boxer » Thu May 16, 2019 4:59 pm

frame side.jpg
frame closeup.jpg
I took a few pictures of the frame support. The bike is an '82 R100RS.

Kevin
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Re: Dellorto PHM38 BD 60/5 + R100RS frame brace

Postby r75boxer » Fri May 17, 2019 1:01 pm

So, a bit off topic but has anyone seen this frame setup before? Both sides are identical and braces are easily removed for engine removal.

Kevin
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'73 R75/5
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Re: Dellorto PHM38 BD 60/5

Postby Rob Frankhamr » Fri May 17, 2019 1:37 pm

So, a bit off topic but has anyone seen this frame setup before? Both sides are identical and braces are easily removed for engine removal.

Kevin


I haven't seen that particular bracing setup before but there are a number of 'kits' on the market of a similar nature. They all seek to tie the front tubes to the rear tubes in some way either with bolt on or welded brackets. It is still my opinion that any effect on frame flexing would be minimal, especially in the lateral sense where it would be most important if there were a need for bracing.

Rob
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Re: Dellorto PHM38 BD 60/5

Postby r75boxer » Fri May 17, 2019 1:55 pm

I would agree. What's interesting is that these look factory or as I said earlier, the best damn welding job I've ever seen. Also, the German fellow that I bought it from said that he'd seen these before as they left the factory. At the very least it's a conversation starter ......

Kevin
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Re: Dellorto PHM38 BD 60/5

Postby Mjolinor » Fri May 17, 2019 1:56 pm

I wonder if it is for a sidecar. I can't see them doing a lot on a solo and I am not sure what they would do on an outfit. Just another of those oddball things that these bikes suffer from. :)

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Re: Dellorto PHM38 BD 60/5

Postby SimonG » Fri May 17, 2019 3:17 pm

My understanding is that the frame bracing was one of the mods used by the racers back in the 'Battle of the Twins' days in the 1980s. I've seem one frame done with it, maybe at Andrew Sexton's place. That had one welded-in bracing strut and the frame-rail underneath it cut, jointed and bolted so it could be removed to help with engine work.
It's not a modification that I fully understand but hey! - I've never raced one.

SG

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Re: Dellorto PHM38 BD 60/5

Postby r75boxer » Fri May 17, 2019 3:21 pm

Sounds exactly like what I have in this bike. As mentioned earlier it has a number of other modifications that I would think only would be done if racing the bike. Thanks for your input.

Kevin
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'73 R75/5
'58 R26
'51 R67

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Re: Dellorto PHM38 BD 60/5

Postby Rob Frankhamr » Fri May 17, 2019 10:41 pm

Hmm,

It's a dangerous thing to say that BMW didn't fit frame braces in factory... A lot of things seem to have happened that were never documented... but I can find no evidence that they ever offered braced frames ex factory on any production machines. Even the pictures I have seen of the works Paris Dakar machines (where bracing might make more sense) don't seem to show them. BMW didn't campaign a road racing team on 247 engined machines (although there were a lot of privateers) so it's unlikely they would have developed them for that purpose. My best guess is that they are an aftermarket add on with... yes... very professional welding.

Rob
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