will 308 roller rockers fit 304 ?

[SRH-420]

i have a set of 308 roller rockers (yella terra) and was wondering if they will bolt to the injected 304 ? if so what are the pro's cons if any
thanks in advance

[DANNY8]

I thought they were different (bolt thread) but tried bolting a set we got off some carby heads onto my VN heads and they fit.

Advantages I guess would be less friction, can handle more rev's, and will give ya more lift if using 1.65:1 rockers.

[VR38]

They do fit but depending on specific types (there are several) you should pay close attention to alignment of the valve tip as the exacting tolerances of YT outweigh GMH, with the different valve arrangement between carby heads and EFI heads the centring of the valves are slightly different.

[DANNY8]

They do fit but depending on specific types (there are several) you should pay close attention to alignment of the valve tip as the exacting tolerances of YT outweigh GMH, with the different valve arrangement between carby heads and EFI heads the centring of the valves are slightly different.

But as long as the valve tip is in full contact with the roller it shouldn't be a problem hey? I never checked mine heaps close....but I'm 99% sure they were all ok. Will double check when I assemble the heads.

[VR38]

Near enough was good enough for Capt. Cook in 1770, why change now lol.
But yeah you are right, if the roller is centred on the valve then yeah no prob, maybe a little off with the shaft mount rockers, not sure how close is good enough tho. they will still work but your wear rates will increase alot with high lift and heavy springs.

[ari666]

you want the tip of the roller rocker to be slightly outward of the tip of the valve. the reason being, as the rocker depresses the valve, the tip will roll off the center and inwards. at full lift the tip of the roller must be in the center of the valve stem.

you can check by smearing a small amount of bearing blue on the roller tip and depressing the valve (crank the engine by hand) whats left should be nice coverage of bearing blue on the valve tip. if its too close to the inside edge you can fix it by either shimming up the rocker or getting different sized pushrods, but its pretty important to get them spot on or there will be too much side loading on the valve and itll wear out your k-lines.

[VR38]

you want the tip of the roller rocker to be slightly outward of the tip of the valve. the reason being, as the rocker depresses the valve, the tip will roll off the center and inwards. at full lift the tip of the roller must be in the center of the valve stem.

ari666 you are correct.
Just to clarify I mean centred across the axis of the roller tip, not centred in the actuating plane, if that makes sense.

[DANNY8]

Well I chucked me donk together just then and put the roller rockers back on for a look (these are yella terra's btw)...and yeah, here's a pic.

Took them back off and decided to stay with the stock rockers lol.

[VR38]

FYI there are two pairs for the old carby heads, two front and two back, if you swap them around does it get any better?

[VR38]

I doubt the tips would roll the way you have them pictured and I could only imagine the side loading on the valve guide... especially to the one pictured on the left.

[DANNY8]

I would go check, but don't really wanna pull the rockers off now that they're on there, all oiled up, and got cam lube on the ends of the pushrods...all ready to go!

[SRH-420]

Cheers for the info guys i will do as said above and check them out. I will let you know how i go thanks once again

[VK_3800]

FYI there are two pairs for the old carby heads, two front and two back, if you swap them around does it get any better?

All the aftermarket rockers I've seen for early heads are symmetrical and fit the same no matter how you swap them around...?

[ari666]

yep, mine are symmetrical, never head of a front or back. if its the case, i guess i just 'lucked it' and got them all right without trying.

?

[VR38]

It states 2x front and 2x back pairs for each head in Yella Terra's fitting instructions and to check you have not mixed them, don't make me dig them out and quote the actual differing dimensions they state.
As from the above photo, maybe you did not pay enough attention when fitting.

[VR38]

yep, mine are symmetrical, never head of a front or back. if its the case, i guess i just 'lucked it' and got them all right without trying.

?

What type are they?
You may be alright with some other types but not race style shaft mount, they come in the box 4x one and 4x the other and will not line up correctly if installed in the wrong place, it will still work and it is not much but it will wear unevenly on the tip and valve guide.

[VK_3800]

I'm pretty sure its the later (VN) heads that have the different ones like you're describing, not the early heads

[VR38]

PFI heads are symmetrical. ie there is no alternating of valve arrangement between the inlet and exhaust.

[ari666]

mine are yella terra shaft mount. they all fit beautifully. all identical. all on old VK style heads.

[VK_3800]

PFI heads are symmetrical. ie there is no alternating of valve arrangement between the inlet and exhaust.

I don't disagree with that, its the slight offset of the valve in relation to the pedestal. There is a photo around somewhere (can't find it at present) which shows it nicely on the Yella Terra rockers, one of each pair has the roller tip slightly off centre