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R75/5 Crankcase breather advice..

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skyler.robbins
Posts: 227
Joined: Sat Sep 22, 2018 4:14 pm

R75/5 Crankcase breather advice..

Post by skyler.robbins »

Hey Gang,
I've noticed that my bike ends up having the turkey gobbler sound after riding around and it's all warmed up. Definitely noticeable when at a stop light.. kinda embarrassing to be honest, hahaha .

So I decided to take the tank off and do some exploring. To my surprise, the bike already had a newer style reed breather installed. Although I am happy about that, I'm also disappointed cause I was hoping to replace it with a new one to get rid of that noise.

At this point, do you think I should remove the existing breather and install a new breather? Pretty much the same thing.
Also, I noticed that the existing breather isn't in the correct positioning from what I've read online. I guess most people feel that the screw should be at the 5 o clock position. I honestly don't see why. If anything, you would think it should be at the 11 o clock position so that the reed is facing more toward the hose. Bit then again, when it's just fumes, why does this matter?

From my understanding, with a new breather and you still get the noise, then there is too much pressure in the crankcase and it might be time to look at rings/valve guides?

Thanks for your input!

Picture of existing breather for reference...
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schrader7032
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Re: R75/5 Crankcase breather advice..

Post by schrader7032 »

I also have heard that the screw should be pointing towards the driver's right footpeg. I think that rationale is more appropriate for bikes like my /7 where the cover over the breather has an exit which runs forward and through a channel in the engine block before being routed back to the single outlet to the right carb. This in-block routing was only used on at least the /7 but maybe some later models. I don't think that was an issue with the /5. I would agree, though, that if the housing on the breather has a hose exiting the rear towards the right carb, then your positioning seems to be fine.

I suppose if you are here with the breather exposed, I might be inclined to change it just to rule it out.

I would certainly consider both a compression and even better a leakdown test. You might find something to confirm the higher than normal leakage past the rings, contributing to the increase in engine internal pressure. What's the status with the top end? Miles? Was it recently upgraded?
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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skyler.robbins
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Re: R75/5 Crankcase breather advice..

Post by skyler.robbins »

Thanks Kurt,
Yeah, like you say, might as well change it out while it's all exposed.
I've only owned the bike for a few months.. not sure on the engine history.
The odometer reads 64,000, but it is reading high along with the speedo due to the ratio not being correct.
My compression is at around 135-140 psi each side.
Although it's a 750cc motor, the heads are 900cc.
Perhaps the bigger heads are too much for the 750 crank case breather?

Thanks again!

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srankin
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Re: R75/5 Crankcase breather advice..

Post by srankin »

Other than the turkey gobble at idle is there anything else wrong with the bike? I mean are you using a large amount of oil or do you have a ton of oil in one or both of the carbs?

Come on, why mess about for only a noise that I just a part of airhead noise in some cases?

LOL, our bikes are so quiet compared to some of the Harley guy's bikes we notice things making noise that is normal and sometimes over react. For example, when I am riding, I don't wear my hearing aids and wear foam inserts. So, I don't hear a lot of engine noise at idle or wind noise or fairing rattle. (yes, I can still hear emergency vehicles and horns). LOL, my bike is as quiet as a church mouse. But, on rare occasions, I ride short distances without the ear plugs, my bike sounds like a loose collection of nuts and bolts rattling in a can. I then rush home, put it on the lift and adjust valves only to find most of the time they are already in adjustment and don't need adjustment. The noise I was hearing was normal and I was only hearing it because I didn't have the plugs in my ears.

Honestly, I would only mess with the breather if you had an oil problem or if it is blatantly installed wrong.

Don't make work for yourself, on an airhead work will come along in its own time. St.
Owner of a 84, R80RT and 78, R100RS

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skyler.robbins
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Re: R75/5 Crankcase breather advice..

Post by skyler.robbins »

Haha.. I hear you.
I think since I went through the trouble of removing the tank, I might as well change it while it's all open.
I'm not seeing the bike burn/use a lot of oil.
There is small amounts of oil flowing into the right carb, but that is to be expected since it is coming from the breather.

Perhaps I'll pull the heads this Winter and do a run though.

Thanks again!

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