Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: royhall on January 14, 2015, 11:54:36 AM
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Bit of advice if you would. The F2 is now very close to completion and engine start day has almost arrived.
The engine has had a freshen up ie. skimmed head and barrels (PO going mad scraping gaskets with a screwdriver), very light hone of bores to deglaze, new piston rings, valve grind-in, new cam chain etc.
Thought I would compression test it before attempting to start now I can spin it over on the starter. Very disappointed with the results as No1 was down at 90psi, but jumps to 155psi with oil in bores. The others are slightly better but still low but also jump up when oiled. Testing was done cold without the carbs fitted, but exhaust on.
Am confident the valve timing and the rocker to valve settings are good, rings were fitted 120 degrees apart.
Is this likely to improve as the new rings bed in, or should I not risk starting it?
Cheers.
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you have fitted new rings,and de-glazed the bores,they now need to bed in together,
after running in,
check this advice
http://performanceforums.com/forums/archive/index.php/t-67139362.html
the rings should have got a much better seal,
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Thanks John. Interesting read that, maybe I am being a bit over concerned. I have rebuilt engines before without any problems, but this time I have bought all the correct tools like compression test gear. Maybe ignorance is bliss where fresh engines and compression are concerned. Everything appears to be okay, engine turns over well and oil pressure light out. Think I may as well go for engine start tomorrow. Spring is fast approaching. Cheers.
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I have recently been in touch with Peter at PACRE racing for some twin parts and saw this on his website which looks useful to me...certainly taught me something but I'm no expert on engines. What do yopu think of this link Graham (Trig) as I know you build a lot of engines.
http://pacre.co.uk/running_in.html
Ash
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Interesting ???. This will explain in more detail > http://www.dailymotion.com/video/x6s8ju_piston-rings_auto
There are many myths on running in a engine but, i always start of slow and then increase the load.
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I can say that Kawasaki rebored a lot of Z1000 under warantee as the owners treated them too gently at the start and bores glazed badly.
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Was the Z1000 on chrome rings with a cast iron bore Bryan ?
Just read the link on John's post and i think 3000 km is a bit excessive. If that was true then the drag boy's would be waiting a long time to run the new build engine in before a 1/4 mile blast ;D.
I bed a road engine in by giving it a 100 miles run all at once but, never over 4,000 rpm. The thing is to get the engine up to running temperature so that the piston is fully expanded. ( short runs are no good ). Then a oil and filter change to get all the running in compound out re-torque the head if it has a copper head gasket and then just build up revs and load.