smoke on over run :-(

[ChrisJC]

My full analysis of the original overrun valve makes an interesting read as to how the system behaves - without a method of vacuum limitation

It is interesting indeed. My flapper V8 in my van has no overrun valve or overrun shutoff on the fuelling, I must try some experiments to see if I can get any pops / bangs from the exhaust.

Chris.

[spend]

...
have refitted the 3.9 breather setup complete with the T piece,
im still getting a bit of smoke but no where near as bad as it was, just get a little wisp when nearly at a stop,

Are you sure its not just the residual crap left in the Trumpet Base / pipework that will take a while to clear through, and that you've actually corrected the problem?

[Coops]

...
have refitted the 3.9 breather setup complete with the T piece,
im still getting a bit of smoke but no where near as bad as it was, just get a little wisp when nearly at a stop,

Are you sure its not just the residual crap left in the Trumpet Base / pipework that will take a while to clear through, and that you've actually corrected the problem?

possible mate,
im taking the plenum top off in the next week or so to remove the rocker covers to check the stem seals,
and while im at it i will also do a compression test. (cold and hot).
snd clean out any signs of oil in the trumpet base and breather system.

[ramon alban]

It is interesting indeed. My flapper V8 in my van has no overrun valve or overrun shutoff on the fuelling, I must try some experiments to see if I can get any pops / bangs from the exhaust.

And therein, Chris, lies a paradox, because whilst there is no doubt why and how the O/R valve on the SD1 was expected to function, based upon the description in the tech training manual, there you are with your flapper setup having no valve, no shutoff and NO POPPING and BANGING.

So does this disprove the science. No! not at all, because my treaty was aimed at explaining what happens on a normal SD1.

Reason being, all SD1 Efi''s that I was aware off had no throttle stop adjust screw, the expectation being that the throttle plate(s) was was set for a tight fit in the tunnel(s).

Yet all the RR engines appeared to have Throttle plate adjustment to leave a small gap between plate and tunnel.

So on Tony's TP set up with NO GAP, I reckon, generates much more inlet manifold vacuum than an RR set up with GAP.

That may, in part, explain why so much oil is being sucked thro on Tony's TP; yet on your SP with a throttle plate gap, there is insufficient vacuum to induce over rich mixture as described in my analysis and therefor, little or no POP and BANG.

Expressed another way, its hard to induce a vacuum in a closed space if the front door is partly open.

[Coops]

BUT,
the stepper motor is slightly open on overun so gives the same effect as the throttle plates open a fraction yes?
also the idle bypass screw will allow some air pass also would it not?
and with the breather hose also connected to the trumpet base as well as the plenum would this not now help?
so its not a complete sealed system on my car.

this is an interesting post

[ChrisJC]

I think an old fashioned compression test and a leakdown test is in order.

Chris.

[Coops]

I think an old fashioned compression test and a leakdown test is in order.

Chris.

will try and do both over the weekend,
on the leak down test, how much psi should i put into the cylinders?

[mgbv8]

My compressor is a wimp Coops!
So I only use around 100 psi with my leak down tester.
All I really do is make sure the cylinder has both valves closed and stick the air supply on. I listen at the exhaust, oil filler cap and then the inlet manifold for hissing!! On my engine I get a lot of hissing from the oil filler. But thats due to my silly big ring gaps. I just try to detect any difference in the sound of escaping air on each cylinder.

To be honest. I lost the instruction manual for my snap on leak down kit. And I only have to use it for other folks cars in serious trouble. Normally the result is obvious on old MGB 4 pot engines.

[Coops]

ta Pel,
its getting close to saying f**k it,
along with the oil prob i now have throttle probs again with it sticking,
god wish i could afford a set of throttle bodies

[Coops]

not had chance to do the comp/leak test as been working on the new throttle linkage,
BUT there is oil in the plenum,
and from memory more than there was with the old 3.9 faithful donk i was running previous.

also speaking to a guy who builds and races RV8's, (his own engines)
he said he had a RV8 that did the same, and was a ring issue,
not damaged just took ages to bed in,
he said they stripped it down and found nothing wrong,
he also said it did over 1000miles before it cured it self,

so not sure what to do now

[katanaman]

comp/leak test first then if it looks like something is wrong you can wonder what to do. It might come back fine and you can start to look elsewhere for the problem. If you still cant find it then an oil catch tank plumbed back into the inlet will work and just call it one of these things.

[kiwicar]

Tony
reading back on this thread and thinking about how you ran it in, I cant see how you would have glazed the bores, they should have bedded in when you ran in the cam, 2 to 2.5k revs for 20 minutes and you should have the rings well bedded in, unless you pootled around with a very rich mixture for the next 100 miles and had half a gallon extra oil in the sump, and you would have noticed that by the cloud of blue/blach smoke folowing you you cant have glazed the bores. Following that you would have had oil smoke on idle and a coaked up tail pipe both of which you seem to be free of.
That leaves valve guides/guide seals or the breather system. I don't know when you last freshened up the heads, but I would look under the rocker covers and see if anything is obvious. However, first I would detach the breather system and see if that clears the problem if so stick a catch tank with a melalised plastic pan scourer in, in line with the pipe into the plenum and if it collects oil in it then that confirms the problem.
Mike

[Coops]

the heads had new stem seals this rebuild,
what we cant work out is,
how come every thing was fine on the 3.9.
but not on the 4.6,
is it down to the engine? bores etc,
Or due to the higher compression ratio?
only other difference on this new engine is im using rhoads lifters instead of the crane race lifters i used on the 3.9.

will try and do a comp test next week while off work, i have to pop the plenum off to modd the throttle arm a bit more, so that will be an ideal time then, as with plenum removed the passengers plugs are easy to get to,

[kiwicar]

the roads lifters will give you alot more vacuum below 4K revs especially on the over run, I recon that is enough of a change to be pulling oil up from the sump. Pull the pipe off the plenum and see.
Mike

[Coops]

should i take the breather pipe off the plenum and pop into a bottle etc,
leave the plenum stub open and try up the road?
if it still smokes not the breathers,
if it stops i need a catch can,