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Timing chest drain

Submitted by david_evans on Thu, 23/04/2015
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Commando

Just studying my timing chest while it's all over the garge floor. (1970 750) The only drain hole to get rid of surplus oil is above the level of the intermediate pinion spindle. The oil seal disc under the crankshaft pinion is a pretty good fit so oil isn't going to return past that in a hurry. this means that the timing chest will accumulate oil whilst running, to a level above the pump and close to the camshaft level. This would explain two things. 1. when given a good thrashing, my Yamaha XS650 breather in the back of the timing chest passes a fair bit of oil. 2. when doing an oil change after running up to temperature. there should be almost no oil left in the sump. the scavenge pump should have cleared it. But a cupful drains down (out of the timing chest) and appears under the sump plug during the next couple of hours.

The Andover Norton website shows mods for the combat crankcases involving drilling breather holes but also a 3mm below the crank (my engine is pre combat) posting on the accessnorton.com website reveals that a 1/4" hole in the bottom rear corner of the timing case may stop the case filling with oil and getting whipped up towards the breather. Jim Comstock who has done some testing on the subject indicates that that oil will run cooler, probably (imo) because it is being recirculated round the whole system and not just working the timing chest. I've just drilled a hole. Thoughts?

Submitted by ian_cordes on Fri, 24/04/2015

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1/4" hole sounds right to me David. I am planning to do the same on my '71 proddie when I start the rebuild. Also modifying the oil pick-up from the crankcase.

Submitted by robert_tuck on Fri, 24/04/2015

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Has anyone done this to a Dommy?, My 99 persists in chucking out oil from the distributor drive area ,although i have not renewed the O ring on the shaft which is the next thing to try.I'm sure the motor would benefit from a bit more breathing capability.

Submitted by phil_hannam on Fri, 24/04/2015

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Previously robert_tuck wrote:

Has anyone done this to a Dommy?, My 99 persists in chucking out oil from the distributor drive area ,although i have not renewed the O ring on the shaft which is the next thing to try.I'm sure the motor would benefit from a bit more breathing capability.

Sometimes the cause of the above is the pressure release valve opening too soon and flooding the timing cover. Try putting in some shims behind the spring in the valve or buying a new spring..

Drilling holes in the crankcase wall may not be a solution. There is supposed to be a certain level/amount of oil in the chest to help lubricate all the bits whizzing round.

Submitted by robert_tuck on Sat, 25/04/2015

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Thanks Phil , Got to take the cover off to fit the seal, so i'll check the pressure rel at the same time .Must be some way to check the pressure at which the valve opens?. .My compressor can be set up to give a pre determined psi , could try that.

Submitted by ian_cordes on Sat, 25/04/2015

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By removing the blanking plug below the pressure relief valve you can screw an oil pressure guage in, which should show you what is going on.

Submitted by david_evans on Sun, 26/04/2015

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Yes Phil but when the oil level is above the body of the oil pump and just below the camshaft, you can't tell me that this is a good situation. That is half a pint of oil that is not circulating in the rest of the system.

 


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