VH45 valvetrain...cam grinding and base ciricle Q's

[Olderthanme]

I was thinking about cam grinding and then looked at the VH45 valvetrain today...

Just looking at the VH valvetrain... How would I compensate for altered valvetrain geometry if the base circles on the cams was changed more than a little bit?Can the rollers in the rocker arms be replaced by rollers with a larger diameter? Are there lash pads under the tips of teh arm right at the top of the valve?

Thanks guys!Dan

[defrag010]

You put shims under the lifter, and use lash caps on the top of the valves.

[T45]

You put shims under the lifter, and use lash caps on the top of the valves.

Lifter = HLA

[Mettler]

You can't really fit larger diameter rollers to the finger rockers, there's no room for them. I'm not sure they were designed to be rebuilt either. Custom finger rockers maybe?

Altering the angle of the finger rockers is detrimental in a couple of ways. Firstly, it increases the risk of having the finger rocker thrown out of the assembly at high revs (I've heard of this happening in the odd stockcar motor).

Remember this valvetrain has a dynamic rocker ratio due to the arc that the finger rocker tip swings through as the cam profile rides over the roller. You'll be changing the dynamic rocker ratio slightly with shimmed HLAs, though I don't know how much by and I think this matters less.

Also, remember there is a tiny patch of machined spherical surface (large radius) on the finger rocker that sits directly atop the valve. Changing the angle of the finger rocker would potentially place this surface at such an angle that only an edge of the finger rocker rests on top of the valve, rather than the smooth machined surface.

Ultimately, I consider cam grinds to be slightly dodgy for this type of valvetrain... which is why I'm designing my own cams with a factory base circle.

[Olderthanme]

Just for me... I don't really like hydraulic lifters. If I could I'd put in lifters from some other engine that were solid, I would. I doubt that it is really feasable.

I was thinking about getting custom made cams but with a cost around $250+ each the cost is quite prohibitive. Maybe I could have the cams built up with welding at a custom cam place (Webb cams or Isky?).

Thanks guys! I'd like to hear more thoughts! I know the dangers of messing with rocker arm angles which is why I want to make sure to get it right.

[Mettler]

I hear 4G63 lifters are almost the same.

Perhaps get your own solid lifters machined?

[Olderthanme]

I hear 4G63 lifters are almost the same.

Perhaps get your own solid lifters machined?

Hmm... Thanks!I'll check that out this weekend at the junkyard!

[SuperHatch]

Hmm... Thanks!I'll check that out this weekend at the junkyard!

I have 4G63 and VH45DE lifters sitting in my garage. I will take pics and measurements this weekend for you.

[Olderthanme]

Superhatch,That would be sweet! Thanks!

BTW I'm looking at adapting a LT1 T56 to my VH45. :-D

[defrag010]

You guys are making this way more complicated than it needs to be. The only thing you have to do is shim under the lifter (HLA for those semantically objective people) and put a lash cap on the tip of the valve so your geometry is the same as stock.... altering and correcting rocker geometry with overhead cam/roller follower heads is easy. There is nothing wrong with smaller base circle cams, the VH is no unicorn motor and regrinds will work just as well if you adjust for the correct rocker geometry.

4g63 lifters aren't solid, and they are narrower and longer than VH lifters. To get solid lifters, you could just tap the stock lifter bore, machine the top of the bore flat, and use L28 style screw-in solid lifters with a lock nut. For a street car or an average/mild motor setup, it's not worth it, and you will see no gains over the hydraulic lifter.

[Olderthanme]

4g63 lifters aren't solid, and they are narrower and longer than VH lifters. To get solid lifters, you could just tap the stock lifter bore, machine the top of the bore flat, and use L28 style screw-in solid lifters with a lock nut. For a street car or an average/mild motor setup, it's not worth it, and you will see no gains over the hydraulic lifter.

I already have 2 sets of L28 style solid lifters(rocker arm pivots...) so just one more set would have me ready for the swap...I'd call my engine a more than mild setup as I'm going to rebuild with forged slugs and prepare it for boost(450-500~ish hp).

[T45]

The only thing you have to do is shim under the lifter (HLA for those semantically objective people)...

Sorry, I think I've been hanging out in the Q45 forum too much.

[mtcookson]

Nah, there's no lifting going on so its an HLA.

[Mettler]

You'd want to drop the base circle diameter down by 2mm radius to allow the peak of the lobe to achieve 12.7mm (1/2") valvelift.

This means reducing base circle diameter to 26mm, actually undercutting the bearing journal's diameter of 26.5.

I would want to investigate clearance to the finger rocker at all stages of lift just to make sure that the body of it couldn't interfere with the cam (probably sweet as)

[Johnny Rocket]

You would need new cores made.........call cammotion in Baton Rogue Lousiana......got money?

[SSDwellah]

I agree that for a high-reving race motor that gets rebuilt often, having self adjusting low maintenance HLAs is a downside. I would say that you should check out a KA24DE or solid SR20DE valvetrain. They were designed around the same time so things might be close than you think (I have already heard that the SR20 GTiR springs can be used on VH, unconfirmed).

Anyway, at least it will give you ideas. Here's an example conversion kit for SR20 HLA http://www.more-japan.com/JUN-....html

[camgrinding]

I was thinking about cam grinding and then looked at the VH45 valvetrain today...

Just looking at the VH valvetrain... How would I compensate for altered valvetrain geometry if the base circles on the cams was changed more than a little bit?Can the rollers in the rocker arms be replaced by rollers with a larger diameter? Are there lash pads under the tips of teh arm right at the top of the valve?

Thanks guys!Dan

If you change the roller diameter, you will change the duration of the cam lobe. Imagine using a larger roller, and imagine it's sitting somewhere on the base circle of the cam lobe. As the cam rotates under the roller, and the opening ramp approaches the roller, the larger roller will contact the opening ramp just a little bit earlier than the smaller roller would have. The effect will be largest when the pressure angle is greatest, i.e. along the middle of each side of the lobe.

We started grinding cams in 1970, and now we are the leading cam grinding company for industrial engines.

We have software that will convert profiles based on the size of the follower, so it is certainly possible to take the roller size into account and grind the appropriate cam profile to use a larger diameter roller.

ClayKams, Inc. - cam grinding for industrial engines

[Mettler]

Good point Clay!

Have you got any opinion on the performance difference between a cam designed to provide the engine with a high dynamic compression ratio, or with a longer duration & overlap for peak power?

I'm sure if you could offer a cam solution for the VH engine with a standard base circle, people all over these forums would jump on them!