Bores - To Oil or not to Oil?

Howard

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On strip down, there seems to be a lot of oil in the bores (fine as long as it's not getting past the rings). I've seen posts in the past that claim the pumped oil supply to the bores is unnecessary, and the feed has been blocked.

Is there a current thinking on this, or will this provoke the usual flood of different opinions?

Howard

ps Merry Christmas and a Happy New Year.
 

greg brillus

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Howard, It will provoke the usual flood of opinions........:)..........However, I always run them, as I did on the racer as well. I don't see how it can possibly do any harm, provided the hole is below the lowermost ring on the piston. Cheers...........Greg.
 

Oldhaven

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First drip in the flood: there should be no harm with later engines but I think with the early two piece head bolts like I have that getting oil tightness may be difficult, even if the oil ends up correctly inserted below the rings. It is difficult to seal the joint between the outer ET 55 and the crankcase insert ET158 when the slots to allow installation and removal of the insert appear to give oil in the feed gallery a direct path right up the inside of the ET55 to the top of the head? One piece bolts are sealed above the groove in the threads when they are installed to prevent this. My feeds are blocked and time will tell if there are problems, but I don't expect any.
 

vibrac

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Put them in without doubt. I know Tommo Tompson a racer I have great respect for does a lot of work to ensure the front of the cylinder gets a supply as well, especially on his four valve Vincents
 

Cyborg

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I just purchased new unfinished cylinder assemblies and I plan on drilling the oil holes with the thought that they can always be blocked off later if desired. I installed the cylinders on the engine without rings on the pistons and calculated where they should go. It works out to about 50 mm from the bottom of the liner. That gets the oil hole 2 mm below the oil ring at BDC and just within the limit of the crankcase mouth. To verify that I was in the correct neighbourhood, I checked an old pair of liners and they were exactly 50 mm from the bottom. However, when I checked the old cylinders from this engine, the oil holes were 61 mm from the bottom. I compared the ring location on my new Omega's and old pistons and in both cases 61 mm would put the oil hole smack dab in the middle of the first and second ring. I guess the moral of the story is that if you are going to have oil holes, you need to verify the location.
 

Robert Watson

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When we rebuilt an A twin that had been done in the UK many years earlier we found that the oil holes came out in the bore pretty much dead center of the second ring and well above the oil ring. No wonder it smoked and burnt oil!
 

greg brillus

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Perhaps this is why many engines used oil from new.....!!!......It's there to lube the piston skirt, not turn the engine into a two stroke..............:).
 

greg brillus

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On the subject of engine assembly regarding pistons, rings and the cylinder bore. Lightly coat the bore surface with clean engine oil, lube the gudgeon pin and big end bush, but do not put any oil on the piston rings themselves. It will help the rings seal quicker on the bore surface, as lubricating them can lead to the bore glazing up. Get the engine to a state of running well enough and go for a blast around the block. Running the engine at low speeds for too long in the workshop will not help the rings to settle in at all, plus the engine will get hot quickly too if it has had an extensive rebuild, I always point a running fan at the engine whilst setting up carb's in particular.
 

brian gains

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on my next build I was thinking of doing the bore/p[son assembly completely dry as have been told glazing is the major factor in a smoky motor being the result. however a light oil on a newly honed bore only does sound more mechanically sympathetic.
 
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