install cam technical question

jstewart
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Joined: Wed Jun 09, 2021 3:30 pm

install cam technical question

Post by jstewart »

Is it necessary to pull the motor to install a camshaft? :?:

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srankin
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Location: Spencerport, NY USA

Re: install cam technical question

Post by srankin »

I believe you can change the cam with the engine in the frame.
May I ask why you would want to do it? Cams in airheads if the oil is changed regularly with the proper oil can last hundreds of thousands of miles before they need replaced. Or at least, that is my experience.

There were a few people who installed the BMW high performance cams back in the day and it does increase performance on a race track but decreases ride ability for normal street riding.

The R90S cam is according to the BMW microfiche the same cam as the /6 and /7 bikes, a good cam for the design that works very well for street riding.

Okay, so I am giving a lot more information than a simple yes or no to your question, sorry, I am just nosey, LOL. St.
Owner of a 84, R80RT and 78, R100RS

jstewart
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Re: install cam technical question

Post by jstewart »

Thanks for the reply srankin. I have gotten several responses from professional shops and yes it is possible but not advisable.
I am going to install a siedelbrock 1000 cc kit in the bike and want a little more cam, probably the BMW 320. Since I have no plans to undo many of the previous owners mods and this is only a R90s in appearance I am doing a few more mods to satisfy me personally.

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srankin
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Re: install cam technical question

Post by srankin »

I have pondered the 1000cc upgrade for my R80RT for years and have not dropped the trigger yet, perhaps next time the cylinders are shot.

You are on the right track getting feedback from BMW airhead shops regarding this upgrade. I would advise to take some of their advice with a grain of salt, remember, they may be trying to sell you more than you need.

I have seen a lot of "modifications" done to other people's bikes at great cost to them resulting in sometimes vast improvement of power and handling, sadly however, also negligible improvements. For example, I raised the compression ratio on my bike from the US 8.5 to 1 up to the European 9.5 to 1 and to be honest, don't notice any difference in performance or MPG. Now, I did the upgrade at a time when the cylinders were shot and I needed to rebuild anyway, so the cost was there, and going up in compression did not add to the build anymore than rebuilding stock.

Getting back to my possible comment about my upgrading to 1000cc kit, I am on the fence because I have not had enough positive feedback regarding the cost versus performance taking apart a good running bike to perhaps improve power. Now, at the time the engine needs another full rebuild, I may then spend the money and go whole hog.

I am chatty this morning, it is raining and I haven't got the ambition to work on my restoration project hence, I am rambling on the forum. St.
Owner of a 84, R80RT and 78, R100RS

jstewart
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Joined: Wed Jun 09, 2021 3:30 pm

Re: install cam technical question

Post by jstewart »

Glad to hear from you on this. I expect to get some additional torque from this as I would from switching from any 900 to a 1000 cc's. The compression on my bike with 900 cc barrels and the larger 1000cc heads also likely is below 9/1. The Sidelbrock kit will raise compression to 9.5/1. Wed intend to cc the combustion chambers and I will have a better idea of final compression then. :D

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schrader7032
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Re: install cam technical question

Post by schrader7032 »

Pushing things to 9.5:1 is getting dangerously close to the possibility of pinging/detonation of the wrong gas is used...if you can get the octane high enough. I opted for the 1000cc Siebenrock kit for my tired out top end on my R100/7. Probably had 9.1:1 compression from factory, but I was concerned about getting too high. So I installed compression reducing base gaskets...probably knocked it back to 8.8:1. Still runs great and I don't have to be concerned about engine damage or needing to dual plug.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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srankin
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Re: install cam technical question

Post by srankin »

Both of my bike now run 9.5 to 1 compression, so far, I have never had a problem with pinging. One thing I am careful of is to use the highest octane gas I can get. Luckily, I have only had to put low octane in the RT one or two times in its life. Then, I took it very easy and still don't recall any pinging.

Now my R75/7, used to ping all the time but only when the points got out of adjustment which is why the 78 RS has the points removed and a electronic system installed. I only have to adjust timing if I take the unit apart. Timing stays where it should and no ping.

In reality, I can't really notice the difference in performance between the stock 8.5 to 1 compression in my RT versus the rebuild 9.5 to 1. Funny as well, there was no big performance gain from just rebuilding worn out cylinders. Of course the oil consumption went down, and the clanging and banging the pistons were making in the worn out jugs went away.

I have never put one of the bikes on a dyno to see what if any gains in HP or torque are. I sure am pressed to feel it in the seat of my pants while riding. St.
Owner of a 84, R80RT and 78, R100RS

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schrader7032
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Re: install cam technical question

Post by schrader7032 »

Then there's the build up of carbon in the combustion chamber which will increase slightly the compression ratio over time.

And your point of "noticing" a difference with the upgrade. I think that is something that people don't really consider. It is, after all, a 1970s design. I don't think there are a lot of spaces in the design to really help the performance out...it's like a zero-sum game. Improve the top end, but hurt the mid-range. So, it seems like throwing money at the bike doesn't really give the return...at least from an engine standpoint. I think the suspension area can be improved with better forks, stiffening the frame, better shocks, etc. There I think a person who pushes the bike will notice the difference. But engine horsepower...not so much. You have to be a Udo Gietl for that! :D
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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srankin
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Re: install cam technical question

Post by srankin »

There have been a lot of guys over the years who made "modifications" to engines, spent a lot of money and felt it was worth it. I am not really one of them. Yes, I did bump up my compression the RT but it was time to rebuild and the cost of higher compression pistons was the same as the lower ones.

I fully agree suspension modifications are worth it even if like me, I don't drag my foot pegs in corners riding at the edge, personally, the street is not the place to be riding so aggressively. So yes, I added a fork brace and beefed up triple clamp, but, I didn't spend mega bucks on super duper high performance shocks and springs, Ikons work just fine for me and my riding style. Same goes for tire choice, I go for long wear over performance as long as the tires perform as needed.

As it is raining here, I am taking up forum space. The great thing is for airhead owners, a great deal of new and improved items out there at reasonable cost and everyone can do what they like with their bikes. Enjoy the riding. St
Owner of a 84, R80RT and 78, R100RS

jstewart
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Joined: Wed Jun 09, 2021 3:30 pm

Re: install cam technical question

Post by jstewart »

Well guys this bike already has numerous handling upgrades the former owner did. The bike was built at San Jose California BMW and they have a lot of experience with this sort of thing. The Frame was reinforced as well as the swingarm and the shocks and front forks were also replaced or modified. I didn't necessarily want this when I went looking for a air head but I appreciate the changes. As for pre detonation problems I am dual plugging the heads so I don't expect to have this problem at 9.5/1 or even 10/1 on 93 octane pump gas. My mechanic Gunther Wuest is a very experienced air head specialist and he assures me we will not have pre detonation problems with this motor. We are also going to install a mild BMW performance cam (probably the 320) which will help with this. Because of Guenther's extensive experience with these motors he is very busy and gets motors from all over shipped in for work, so I expect it will be a couple of months before he gets to my work. I will get back to the forum to report on the results. Again because of all the modifications (frame, suspension and others made at San Jose BMW) this is not a concours restoration R90s.

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