New product
- Thread starter comnoz
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Ok..............just thought that an breather open to atmosphere fitted into the bottom of the case at the back, may have vented some of the oil in the cases in some situations?
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The oil doesnt tend to run to the back of the cases when accelerating hard then I guess?
john robert bould said:
46 years ago ? That would make it an Atlas, wouldn't it ?
The Mk111 was advertised as having wider and improved jointing faces and that does indeed seem to be so in most areas.
My Mk111 came back bone dry yesterday after several hundred miles in the rain so it would have shown if it was sweating and I don't normally have a problem. They are not however immune to leaking tacho drives as things wear (mine now has an oil seal)
750s in particular seem to be much more prone to leaky faces.
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Jim - just brilliant.
I had one of those moments where you say to yourself "Why didn't someone think of that a long time ago?"
Won't fit on my '73 750, same as '72 - small sump drain bolt.
I had one of those moments where you say to yourself "Why didn't someone think of that a long time ago?"
Won't fit on my '73 750, same as '72 - small sump drain bolt.
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Carbonfibre said:
I am sure it does. But since the engine is not lubricated by the oil that is laying in the sump it would cause no problems. If the oil in the sump gets deep enough to touch the spinning crankshaft then you are in big trouble. I will immediatly whip it into a foamy mess which the scavenge pump cannot remove. I have run into that problem before when designing my own cases. That also happens on the 72 cases unless they have had the pickup moved to the rear. Jim
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Just so these folks understand, how much oil do you think is in the sump of a running engine?
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xbacksideslider said:
If you have a small sump drain bolt then you should have the breather on the back of the case. Right?
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My bet is that either one of Jim's reed valve breathers, will outpace the stock scavenge pump and together the two systems - reed and pump - will outpace the high side/pressure pump's capacity. There will not be any oil pooling nor backing up onto the rear of the cases on acceleration. Remember, we have two pistons trying to push 750cc of swept volume down and out the reed valve and, with the reed valve closing on the upstroke, creating a vacuum, when those pistons reverse direction, those reeds snap open, pulsing oil back to the oil tank.
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79x100 said:john robert bould said:
46 years ago ? That would make it an Atlas, wouldn't it ?
The Mk111 was advertised as having wider and improved jointing faces and that does indeed seem to be so in most areas.
My Mk111 came back bone dry yesterday after several hundred miles in the rain so it would have shown if it was sweating and I don't normally have a problem. They are not however immune to leaking tacho drives as things wear (mine now has an oil seal)
750s in particular seem to be much more prone to leaky faces.
Maths is getting hard on my worn out grey matter....36 years ago.
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swooshdave said:
Yes, I had the breather on the back of the case. I modified an XS650 breather to fit there and it works very well, no more leaks or weeps - at all. I can clear the wet sump with three or four slow kick throughs before I start the engine. If I leave the oil cap off, the second kick will spurt oil all over the back of the bike. By the fourth push/kick through the sump is cleared.
The modification required fabrication skills/tools/time, was not easy, and the fastening is just OK, I used the same two bolt holes that fix the stock breather elbow to the case; they are barely adequate for the additional mass that is now hung on them. Jim's machining of a pad and tapping for 4 bolts in that area is better. The good part is I was able to do it with the engine in place and without case splitting; JIm's new product beats that hassle too, except for the small drain plug 72s and early 73s.
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Jim
thanks for clarifying that this product replaces the sump plug; and of course when I reread the posts it was obvious (I guess the fact that I couldn't figure it out from the photos shows how often I have had a crankcase apart). Again, a great product; and as is so often the case, a really interesting ongoing debate and analysis of the way things work.
thanks for clarifying that this product replaces the sump plug; and of course when I reread the posts it was obvious (I guess the fact that I couldn't figure it out from the photos shows how often I have had a crankcase apart). Again, a great product; and as is so often the case, a really interesting ongoing debate and analysis of the way things work.
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swooshdave said:
The best I have been able to measure in a running Commando it is around 4 to 6 oz in the crankcase and another 8 oz in the timing chest. After drilling the return hole lower I get around 4 oz in the timing chest.
There is less oil in an Atlas sump and timing chest because the vertical engine scavenges better.
If the Commando engine had been designed from the ground up to be mounted at an angle it would have certainly had the scavenge pickup and timing chest drains located in a better place to get more oil out of the motor. Jim
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comnoz said:
Run to the kitchen and grab a 3/4 measuring cup (sorry, no idea what that is in the rest of the world). Stare at it and realize how little oil that is. :mrgreen:
rvich
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If one where trying to decide whether to machine or not to machine, are there any advantages that are not apparent? The only draw back I see to the new product when comparing the two is the hose fitting underneath the engine where it might suffer some neglect from those of use who don't get down there very often. The breather on the back of the cases on the other hand is nearly impossible to get to with the gearbox in place. It appears that the size of the reeds in the new product are smaller than in the original Comstock Breather. What kind of impact does this have? If any?
Thanks,
Russ
Thanks,
Russ
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Ugh, I can verify its impossible to access Combat breather with gearbox in the way and can't remove gear box until engine moved forward ugh. After all my hi centering play off road and hang ups loading in PU's and trailers I'm a bit pensive to anything that can snag under the frame. Moving Combat breather off rear of crankcase is one of the best things to make servicing on bench a single item affair. I read that the best year for motorcycle sales was '72 and that more Combats sold-made than any other C'do version. Their breather is major exit to empty sump oil so glad to know Jim's reed valve can tolerate and allow oil to return to tank too.
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