Inliners International Forums General Discussion Engines 216 v 235 rocker arms

just wondering if 216 rockers will interchange with 235/261 rocker arms?

only if the 235 was a 41-49 version.

So no, the hi-lift rockers on ebay right now are not for the later 235/261 engines...

Mark,

The Master Parts Catalog, (page 139) (page 140) shows different part numbers for the 216s and 1950 and later 235s and 261s. I should know what the difference is, but I can't recall what it is. i will consult my Hollander. Brian finally shamed me into getting one.

Hoyt

It's been suggested I build roller rocker assembly's for the 235 and 261 engines. I built the entire rockers/shaft/stands for my GMC and they work great. After 20 pulls on the dyno, 6 runs down the strip and numerous times starting, the lash stayed perfect.

I wondering if there's a market for them. I'd appreciate comments.

Ron

I do know a few people looking for them.

Why not conduct a poll to see how many people would buy them.

I'd take orders with 50% up-front before committing the build.

As you are aware, they do pop up on eBay from time to time.

I never knew the difference b/w the rocker arms, just thought they were indeed different.

Thanks everyone.

I'd be interested in a GMC set if they don't cost too much. Do you have any idea on price? Tom

Tom,

The set I built was labor intensive and would cost too much. If I could build several sets I'd farm out some of the machine work and get the costs down. The ones on my engine have a ratio of 1.85:1 so I could get the lift I needed. However, the ratio could be whatever someone needed.

Panic is correct on cam loading being directly related to spring pressure and rocker ratio.

I'll do some more research into this and see what I can come up with regarding cost.

Ron

I actually made new rocker stands and located the larger (1.00") shaft closer to the pushrod hole to get the 1.85:1 ratio. I used the existing stand mounting holes in the head (2 bolts per stand). The roller tip offset for the intake and exhaust was achieved just as Panic said in step 5 above.

I did open up the pushrod holes in the head to be safe since I went to 5/16 heavy wall, Smith Brothers pushrods.

I used the larger 1.00" shaft to keep things rigid and eliminate the end rockers from moving around like the stock ones do.

I expect the complete roller assembly will be in the neighborhood of $1000. Kinda expensive but their not being mass produced for the GMC.

Ron

$1,000 for a complete assembly is about what I was thinking. That's not too much.

Ron,

I would definitely be interested in a set (maybe two sets) of roller rocker arms and shafts for a 261. I am not looking for much, if any, increase in lift ratio if the pushrod holes would need to be enlarged. I ruined a head once enlarging the holes for a set of B&B rocker arms back in 1957. If the shaft could be offset as suggested by panic in step 7 I would be interested, depending on how much lift could be put in the cam lobes. I would also be interested in a set of roller rocker arms for my 12-port head on my other 261. I understand that the existing rocker arms used by Wayne Horning et al. are from a 1941 Buick straight 8. I live in St. Louis, so a trip to KCMO would be fairly easy for me.

Well Ron it looks like you've got yourself a business proposition going here
I think I could safely say that there'd be another 6 or so guys around who would also be interested in a set, once word get around.

Damn...looks like I stuck my foot in my mouth again. Tell you what I'm going to do; I have some health issues that have to be addressed this week and I won't know my next weeks/months treatment until I see the doctor this Friday. Assuming all goes well I'll see what I can come up with.

Ron

Good luck to you!! We can wait while you take care of yourself. We've waited this long and health is far more important. Tom

While everyone is holding their breath: the possibility of adapting an existing roller rocker isn't great, but it might be there.
1. the O/A length still has to match the stem-to-pushrod distance
2. all aftermarket rockers will have bigger shafts, so either make one or bush them down to .792" for the Chevy shaft
3. the exhausts are easy, since the Chevy stem angle is very close to some existing rockers at 14°
4. the intakes will be tough, since it angles backwards by 5° - I can't find anything useful that does this. A possible cure is to just use a longer adjuster (more exposed body); this isn't suitable for X-high springs, though

the stock ratio is about 1.42 according to my measurements. An honest 1.5 ratio would be nice.

If you can produce a setup for under $500, they should sell fairy well.

Playing the devils advocate, I would want to see some dyno results that show it's worth it though. Most people running these engines don't spin them past 4000 rpms, so I have to wonder about there ultimate necessity...

Ron, when I built mine I moved the shaft over .100" also. I kept the Donovan Chrysler adjuster ball directly over the center of the push rod hole and used Isky roller tips with their pins and keepers. I used a stock shaft centerless ground down .002" to fit 2 narrow roller bearings I bought from King bearing at the time.(gap in the center for oiling) I was trying for a 1.7 ratio but ended up 1.63 ratio measuring the valve lift to the cam lift.

Yours must be farther off-set since you elongated the push rod holes.

I have a 2 sets of original NOS Thomas Hi-Lift magnesium rockers I've never used. They are just shorter on the short side and would need to have the holes larger if using larger diameter push rods. I believe they were intended to use the stock push rods and were probably OK for a stocker looking for a little bit extra power. Some day I'll put them to good use. Right now I'm keeping them from the hoarders.:)....Good Luck JD

I think being able to get all 12 rockers to have the same ratio would be a huge benefit in and of itself. Even the actual error in ratio and consistency in a stock set of 12 is going to make it worth doing. I can CNC a set of either the Chevies or GMC relatively easy, with a minimum of fixturing. Just buying the roller tips and pins and adjusters is the main expense. If Ron has a drawing of what he has in mind for the GMC's, its pretty much a slam dunk as far as me making a set to help out the cause....

Based on examining the hot cam profiles, the exhaust is generally hotter by 10-15°, and assumes the same rocker ratio for both.
Current thought is that lift is far more important on the intake valve than the exhaust (where the opening point is the single most important factor), which means that (although consistency is always good) more lift isn't cost effective, especially if it means making a very different piece (ref: geo angle).
However: if you only do the intakes, that automatically increases the intake's effective duration, especially the overlap - so it reduces the in/ex bias.
No easy answers.

Realisticly the benefit from increasing the rocker ratio on a stock engine is marginal at best. Normally the ratio increase is benefitial only when more lift is required to take advantage of better airflow at higher lifts. The trend lately is to reduce the lobe lift and increase the rocker ratio to get the desired valve lift.

The best way is to flow the cylinder head then grind the cam for the duration/lift, you need. Just changing rocker arms won't show an increase in performance if the cylinder head can't use the extra lift. However, in my case Dema Elgin had to gring the cam down to the very core diameter to get the lift I needed, even with the 1.85:1 rockers. Trying to get 0.620" lift on these old engines is pretty difficult, especially with a flat tappet cam.

Does anyone have any flow numbers on the 235/261 heads? From talking to Kevin at the shop the head isn't conducive to porting of a serious manner. Water is pretty close and the short-turn is bad.

It looks like I have some research to do. The GMC is pretty straight forward and I have a working model, etc to work with.

Ron

Ron, I already have an intake and exhaust port model in 3D for an 848 head, and am working on getting some flow #'s for it as we speak. I will be blending 21st century technology with these older heads to see what benefits await to be discovered. I also am going to use some Lump port techniques on them as well. I also have a 302 GMC head to do the same thing to as well. Im sure that you bowl cut under the valves on your head, what size did you end up making the bowls for the intake and exhaust.

I'm trying to find an 848 casting locally bad enough to scrap, but good enough to saw up in a few planes to find where the ports can be improved without getting a bath.
According to Bell, for a siamese port the area should be slightly larger than the valve area, so if a 1-7/8" valve is used, the port should be something like 1.90" ID, which of course is impossible (this is 60% larger than the existing 1-1/2" port). It looks to me that the port ID may be the real choke point that makes any major revision of the intake unproductive.
This is why the lump port works on the 250/292, and not the 235 - the much wider late port has enough area that some can be traded for a better shape; with the 235 there's no room at all.

I agree that more peak lift won't help if the port doesn't flow enough, but a higher ratio also "stretches" the entire duration and especially the overlap triangle area and IMHO will help a mild engine with a stock cam.

Ron, mine ended up .610" at the valve with a flat tappet.

CNC.... As soon as I'm up and around I'll get to the shop and dig out that info. When I was younger I would have remembered it.

Panic.... I agree with your comments. However, I don't feel the cost justifies the small increase in power. Spending the same amount in other areas will give a better return for the buck. I'm a poor boy and have poor ways.

Jimmy six....I've always been impressed with what you've done with your roadster. 216 and change is damned impressive.

NOTE: To anyone reading these comments; bear in mind that the above 3 gentlemen have years of experience and untold amounts of knowledge. Anything they tell you can be taken to the bank. I wish the 4 of us lived close together so we could share our knowledge. I'd be the lucky one since I'd be the one that learns the most.

Ron

Afterthought: on the Gen-3 engines (250/292) the lump benefit (viz. reduced area traded off for improved port efficiency at the SSR) is also partially derived from the removal of an obstruction that doesn't exist in the stovebolt (235): the head bolt boss.
Many engines (Mini, Ford 2.0 L4) have been ported by insertion of a whole new port made from a chunk of Schedule 40 etc. right through the existing iron to intersect the throat at a good place. Since neither the head gasket surface nor the chamber wall is compromised, the seal between the new port and the casting only needs to be liquid-tight against thermostat pressure + safety (30 psi?).
The usual cautionary remarks about pre- and post- heating of cast-iron for welding of course apply, but I don't see why this has to be welded (i.e., fusion using ferrous rod), or even brazed, since mechanical strength isn't the problem. Good silver solder would permit this to be done with far lower temperatures (both pre-heat and actual work conditions), less warpage, less corrective machine work afterward, etc.

I agree that the cost per HP for a roller rocker on a stock engine would be too high - but that won't stop buyers who are simply looking for something to do without a complete R&R!

The rocker is far more valuable for racing, where lack of lift + the flimsy construction of the original make a quality replacement a "must-do", rather than a fashion accessory.
Take my word for it - just because the rocker doesn't actually disintegrate under high RPM and 300 lb. springs doesn't mean that the valve is tracking pushrod and lobe motion accurately. With the stock rocker, a portion of that hot cam never reaches the valve, and another part gets there at the wrong time.

following for results down the road.