valve tops

ANDY178 · Post by **ANDY178** » Fri Sep 02, 2011 7:20 pm

can anyone tell me whats happening here, all four exhust valve tops on one bank, i have replaced them and engine is now running fine,

mgbv8 · Post by **mgbv8** » Fri Sep 02, 2011 8:11 pm

They look like they have split due to spring binding mate???

If you have more cam lift than the springs can cope with the spring coils close up and hit each other just before you get to full lift.

If its only one one head you have to look at shimming the rocker pedestals. Maybe you have one head skimmed too much??

If it doesnt do it on the other head then something is out of kilter.

You need to check rocker clearance before you build again..

ANDY178 · Post by **ANDY178** » Fri Sep 02, 2011 8:28 pm

do you think it could be down to the valves bouncing when i am racing. i race oval circuit and basically leave the car in second and thrash it around an oval track for 10 laps.

mgbv8 · Post by **mgbv8** » Fri Sep 02, 2011 9:26 pm

I only know what my RV8 will do for shot bursts of 10 seconds...
But that looks like not enough clearance combined with a lot of heat and expansion. Is this problem on the head that is closest to the infield on the oval ??

ANDY178 · Post by **ANDY178** » Fri Sep 02, 2011 9:31 pm

sidecar · Post by **sidecar** » Sat Sep 03, 2011 12:02 am

The sintered metal retainers are not as strong as the older 'machined from solid' jobbies, if you are buzzing the engine over 6 -6.5k RPM then personally I would not use them. Also they don't suit dual springs all that well, the inner spring sort of fits but it does not seat very well. You are REALLY lucky that you engine did not drop any valves, that would have been the end of it!

ANDY178 · Post by **ANDY178** » Sat Sep 03, 2011 11:52 am

i replace the four with early sd1 tops, (the solid machined ones) as advised buy a friend of mine, i managed to change them without taking the head off, the car runs mint now,

kiwicar · Post by **kiwicar** » Sat Sep 03, 2011 5:10 pm

Hi
as a thought, you say you run it in second at high revs for 10 laps, are you over pumping the hydraulic lifters? what oil pressure are you running while you are racing? if you are sitting above 5000 revs for the whole race then it could well be pumped up lifters causing the valve caps to hit the tops of the guides.
Besr regards
Mike

ANDY178 · Post by **ANDY178** » Sat Sep 03, 2011 8:47 pm

At the moment i have no instruments in the car , just a two switches start and stop

so i have no idea of the oil presure or the max reves i get upto . The engine was a twin plenum vittesse lump with fast road cam. i have fitted a lightened flywheel tubular manifolds and a 4 barrel Holley. nothing else has been done to th engine. The engine is reving so high at the ends of the straights it starts to misfire and crackle just before i let off for the bends. I am thinking the engine just carnt cope with reving so high, But thats whats the oval circuit racing is all about, I am racing tomorrow so i will see how things go.

DaveEFI · Post by **DaveEFI** » Sat Sep 03, 2011 10:53 pm

Assuming the engine is standard, you'll get lifter pump up before the rest of the valve train gets into problems. Unless you're changing down a gear and pushing the engine beyond that rpm.

CastleMGBV8 · Post by **CastleMGBV8** » Sun Sep 04, 2011 12:32 pm

Andy,

The standard lifters will pump up as Pete mentioned and if you gave not reduced the height of the valve guides the bottom of the spring retainer can hit the top of the guides or the springs will reach maximum compression which will cause the problem you are having, the valves will also stay open when the lifters pump up ahich would also explain the misfire.

Advice,

At least get a tacho and oil pressure gauge! and do the mods to the valve train to prevent further problems, if you are going to hold high RPM for extended period you need proper double valve springs and associated hardware plus high rev lifters from Crower or Crane and the lifter end of the pushrods need to have the chevy size ball end.

You can get tubular pushrods from Real Steel + a set of chevy size ball ends to swap over for the hi-rev lifters.

Kevin.

sidecar · Post by **sidecar** » Sun Sep 04, 2011 2:45 pm

CastleMGBV8 wrote:Andy,

The standard lifters will pump up as Pete mentioned and if you gave not reduced the height of the valve guides the bottom of the spring retainer can hit the top of the guides or the springs will reach maximum compression which will cause the problem you are having

Kevin.

Hi Kevin,

It wasn't me that mentioned 'pump up'....I suspect that this is the only thing stopping the engine going off like a grenade anyway!

Cheers,

Pete

ANDY178 · Post by **ANDY178** » Sun Sep 04, 2011 9:08 pm

The car went ok today, best its run for last 3 meetings, But its still crackles when i hit the end of the straight. I have got an engine which i bought in a car last year and on the rocker cover it has a label, Engine prepared buy Rover Craft England. This is what i got my lightened fly wheel and tubular manifolds off , i have taken the rocker cover off and it looks like brand new, The valve tops are the early machined ones but it only has single valve springs. i have no real knowledge about rover craft and what they did to there engines. can anyone enlighten me of what to look for without taking it apart.

CastleMGBV8 · Post by **CastleMGBV8** » Sun Sep 04, 2011 10:57 pm

Pete,

Yes it was Mike

and your right about the lifter being the only thing stopping it going bang, can't be going that fast in second gear tho' 65 MPH? wonder what the gearing works out at.

Kevin.

CastleMGBV8 · Post by **CastleMGBV8** » Sun Sep 04, 2011 11:01 pm

ANDY178 wrote:The car went ok today, best its run for last 3 meetings, But its still crackles when i hit the end of the straight. I have got an engine which i bought in a car last year and on the rocker cover it has a label, Engine prepared buy Rover Craft England. This is what i got my lightened fly wheel and tubular manifolds off , i have taken the rocker cover off and it looks like brand new, The valve tops are the early machined ones but it only has single valve springs. i have no real knowledge about rover craft and what they did to there engines. can anyone enlighten me of what to look for without taking it apart.

Could be good but hard to tell without checking build spec, the single valve spring are fine for fast road use but will not hold up under sustained high rpm, they will go soft and you will get valve bounce.

Kevin.