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dbinder

Crankcase Pressure - Crossflow

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dbinder

I have recently rebuilt my crossflow engine.  Prior to rebuild there was high pressure causing oil to blow out of breather and also to seep out of rocker box past the gasket.

I have rebult all of bottom end, reground valve seats and replaced all relevant gaskets etc. Rocker box gasket is on using evostik on box and clean surface to head.

I am still getting as lot of oil into the breather bottle (fairy liquid type!!;) and some seepage from rocker box.  This makes for a very untidy and oily engine bay.

The only item I did not replace was the piston rings, all tolerances seemed to be OK and the oil rings were in good condition.  Should I have replaced the rings as well? (Oh no not another engine and gearbox removal job!;).  Any suggestions welcomed.

Dave Binder

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Buzzer

[Prior to rebuild there was high pressure causing oil to blow out of breather ] well IMHO  is usually pistons or rings. how bad is the blow by/pressure. if there is smoke coming out of the breather I would be worried, but if it is just oil carry over or pressure perhaps the breather arrangement is not right. Xflows do tend to throw oil out of the breather. Check other threads on Xflow breathers.

Did you take the rings off the pistons and check clearances?

But if you do what to change the rings, you can without taking the engine out. safely jack up the car. take off the head, sump, undo your bigend bolts and pull the pistons out. Not done it on the Westie, but on other cars OK. hope this helps

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Richard M Green

Dave,

Most Crossflows breath heavily. In my experience the tricks are:

Run 2 breathers; one from the rocker box and one from the standard 'tin' breather on the side of the block.

(Some people run  a pipe between crankcase and rocker box and a single breather from rocker box to catch tank.)

Breather pipes should be at least 5/8" diameter.

Get rid of the Ford flame trap valve which presents a constriction to the block breathing.

Make sure that the block breather has a deflector plate to stop oil flung off the fuel pump drive 'cam' from flinging straight into the breather can.

Use a decent baffled sumpp.

Don't overfill the engine with oil.

HTH

Regards all

Richard

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stu999

Yep, the previous owner had the engine in my Westy rebuilt for the same reasons, and was exactly the same after rebuild. As Richard suggests (I did 'version two'; block to rocker cover, another from rocker cover to catch tank), which stopped the engine blowing oil out of every seal and filling the catch tank every few hundred miles, after the above plumbing the engine was perfect.

Cheers, Stu.  :)

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dbinder

Thanks for help.  I take it that by the flame trap you mean the non-return valve on top of the tin box?  Also worth mentioning that this problem did not occur pre rebuild or post until I upgraded the carbs from a 32/36 DGV to twin Dellorto's.  I presume that the increase in power etc has simply amplified the problem.

I will try the ideas mentioned.  Again many thanks.

Dave

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