74 replies to this topic

[nicklouse]

Sorry just get it pulled. You have problems that adding breathers to will not fix. 
 

a quote from Mr Calver.

 

Another often asked about subject - engine breathers and what is needed. There are those that go the multiple drain-pipe sized option, may be multiple 1/2" breathers. The reason flagged up is to relieve crankcase pressure. This is one of Graham's personal race engines. Note the single 1/2" take off on the rocker cover. That's it. This engine produces very tasty power. Essentially, if you are experiencing a high.level of crankcase pressure, the piston rings are not sealing and you are giving away performance. Discuss.

 

[BobbyMax]

I get that nick, and im pretty much resigned to the fact that engine will need pulling howeve, can i rule out blow-by befor i pull it by adding another breather?

[Shooter63]

Not trying to teach you to suck eggs etc, but you haven't simply over filled with oil have you? These engines don't like that at all, as others have said try running it with the filler cap off, to see if that calms it down, at least you will have tried the simple things first.

 

Shooter 

[Earwax]

As Spider mentioned- if your readings are accurate in Leak down - they are unacceptable ( it is hard to get accurate readings on some cams/ the pressure rotates the engine)  But maybe worth dripping a few drops of oil down each spark plug hole and then and do your  rev to 3200 to see if immediate difference?  Also - check the new rocker post for alignment of holes ( sadly don't assume new equates to all good) 

[BobbyMax]

the only other thing thats just struck me now is i was advised to remove the shims from under the valve springs when I changed the cam.. worn MD286 for a newer one. Im wondering if that's causing valve float a higher rpms.

[BobbyMax]

So firstly i need to apologise for a bit of misinformation due to my stupidity and not reading the leakdown tester instructions fully and testing the engine when cold! 😬

Anyways I've tested again with a warmed up engine, three on around 5% one on around 7% loss

Removed oil fillercap and dipstick and ran engine as some suggested no real pressure from either .Also put a bit of hose on breather chimney to take is away from fan to see if its chugging loads of pressure.
Now to be honest, although i don't realy know how much pressure is to much pressure although there was obviously some positive pressure it didn't seem at all excessive
to me

At the moment im leaning towards some valve float at higher revs as mentiond in my post/comment above....?

[PoolGuy]

So now put things back as they were, see if you can replicate ‘spewing loads of oil’ then change one thing at a time.

[Aridgerunner]

Can someone explain to me how valve float could cause oil to flow out of the breather tube?

[nicklouse]

Can someone explain to me how valve float could cause oil to flow out of the breather tube?

 Can’t see it doing anything. 
 

but it does sound like the springs might not be suitable for the cam.

 

but this leads me onto more questions. What breather is it? If original has it had the wire wool removed? Did it have a hose attached?

 

so much info that has not been given by the OP.

 

If the engine is in good condition one breather is enough.

[BobbyMax]

I thought the the same Aridgerunner, however,after looking into it apparently if you get valve float which usually happens if you valve springs are not strong enough to close you valves quick enough (especialy if combined with a high lift cam) it can let gasses escape up the valve stems past the VS Seals into the rocker cover then down the pushrod tubes into the crank then up through the engine breathe.Or atleast thats how it was explained to me.

If im wrong im sure someone will let me know.... which i will be happy with as long as I can solve my problwm

[BobbyMax]

Hi Nicklouse bit more info for you

1. Originsl kidney crankcase breather with wire wool intact vented to atmosphere NOT carb

2. KC MD 286 cam

3. 1293 cc rebored 100 miles ago new +20 pistons and rings.

4. New valve guides and seals, head skimmed and Victor Rinez Hg fitted

5.New rocker shaft And rockers. Changed from small foot to big foot pressed steel rockers as some of the old rockers were a bit worn

6.Removed Shims from under double rocker springs.

7.Adjusted cam timing by 1 degree.

8. Compression on all pots around 150psi

9. Leakdown test showing 5 to 7%

Think thats it.

Edited by BobbyMax, 15 December 2025 - 09:02 PM.

[Earwax]

Hi Bobbymax   .   Valve float normally occurs at the top of the rev range - not at 3200 rpm.

 

I dont know if the next option is actually available in situ ( without pulling the motor) but could the grub screw at the centre of the cam (timing end) of the been omitted or come loose?

[BobbyMax]

Forgot to say also changed cam followers, new ones have holes in them,the old ones didnt.

Edited by BobbyMax, 15 December 2025 - 09:48 PM.

[BobbyMax]

Hi Earwax, sorry to be a pain but im not quite sure if your talking adout the cam thrust plate or something else?

[Gaz66]

A pointless and unhelpful reply from me but.....

I haven't seen this much head scratching in a while on here 😁