Glad you got it figured out.

Mike

 

Well, 125lbs on the seat is probably not THAT far off from what you need with a hyd flat tappet cam, IF thats what you really have. I would check the installed height and see if they really got it set at 1.9". If not, you may be able to shim up your springs some and get the job done, since you're not running that much lift, you'll just need to watch for coil bind. Also check the open pressure and make sure it's atleast 320lbs or so. If the heads have big heavy Chinese valves in them, you may need more spring pressure. Also make sure to use GOOD oil with lots of zinc.

I think you are on the right track with investigating the valve train/springs, as I mentioned in post #33.

 

Are you absolutely certain that your carb is opening fully when pedal is depressed for WOT?

 

Yep. Had a helper sit in the car and push the pedal while I poked my beak over the carb.

 

I also need to add a spring seat cup. Shaw City Engines put the springs directly on the bare aluminum heads.

 

Wow.. I'd definitely question the work they did then.

 

"Wow.. I'd definitely question the work they did then" Probably my fault. I did not give them specs on the springs- except I needed 0.550 lift capability and that I was on a budget. So- they went low end on the springs. But- undercut ss valves swirl polished, 11/32 stems, 0.100 in longer, stellite seats, 5 angle valve job. SCE has three generations of the family involved in a company around for decades. Immense inventory of heads, blocks, components. If I had given them specs, they would have done better.

 

I'd definitely go through the head setup again. Measure your installed height after adding the spring seats, the addition of the seats may "shim up" your spring pressure a little and that may help you.

You need the correct springs, and the correct installed height for THOSE springs to yield the pressure you need for THAT cam/lifter. Also consider your valve weights and rocker arm weight etc..

I think/hope this is where your RPM problem exists.

 

Agree 100%. Basic cylinder head 101 tells you that a valve spring can not sit directly on the head or it will eat away at the aluminum while running. You must have a spring shim or better yet cup or locator.

 

Parts are ordered. I'm waiting patiently for the FedEx driver to drop off the new springs, retainers and spring cups.

 

I hope so too. I've gone thru fuel, ignition and now valve train to fix an un-expected problem. It doesn't leave much else to check.


This is the first time I did a re-build without sourcing and buying all of the components myself. I think it will also be the last time. I got a good deal on the aluminum heads- and they were first rate- but if allowing the machine shop to pick the valves and springs turns out to be the problem, I wasted a couple weeks on the deal.

 

Did these heads have ProMaxx milled into the ends of them? Also going over the combination. With flat tops, a normal .010" in the hole and with what we see in combustion chamber size on these heads at 121cc this engine is under 8 to 1 compression with a .040" head gasket.

Have you run a compression check to see what it is pumping for cylinder pressure?

 

I'm waiting for spring shims and correct valve stem locks for 11/32 valve stems to arrive, but today I removed one of the offending springs on my heads. I got a ball park installed height with my vernier caliper of 2.15 in (stock height is 1.90 in). I found there actually was a spring shim under the spring that was not visible with the spring in place, so the shop was not as careless as I thought. The specs for the valves state they are 0.1 inch longer than stock and the spring, when removed, is about 0.1 in longer than the Comp springs I intend to install. However, the installed height is still way off. When the micrometer spring height tool gets here I can get some precise measurements and install the new springs correctly. This will be the last time I rely on someone else to do work without double checking it. I have wasted a month figuring out why a simple head installation would not work.


However.....this fiasco does meet my basic motto: "It's a good repair job if you get to buy another tool." New tools for this job: micrometer valve spring height tool, different valve spring removal tool, air pressure fitting and hose to remove springs with head on car. New/upgrade parts: HEI distributor, Holley fuel pressure regulator, Holley billet fuel filter and pressure gauge, Comp valve springs, retainers, shims and locks, Crane valve spring seat, Autometer electronic tach. WTF, it's only money.

 

LOL, I also love buying tools as needed.

 

Well, these are some of the tools I added to my collection. That micrometer valve spring height tool is pretty slick and the valve spring compressor is much faster than the one I previously used. A Moroso valve seat pressure gauge is also on its way. Much of this is due to my haste to install the new alum heads without checking the work done by the machine shop. Changing springs and checking height is easy to do on the work bench. But now I am doing it with the heads on the car and have to take care not to drop any small parts and have to put up with my air compressor blasting away to keep the valves from falling into the cylinder. One side is done, tomorrow will finish, check the actual seat pressure when my tool gets here and then back to the dyno to confirm my high rpm power loss is finally fixed. Fingers crossed. RA

 

Good job Ron!

Its a pain in the *** for sure but it must be done. Verifying spring pressures at a certain installed height, and then setting it to that installed height is the key. Also, remember you lose 5-10% of the spring pressure after the springs are "broken in" so...

I'm pretty sure you're gonna finally solve your problem this time. I'm hopeful anyway. If not, I wouldn't know what else to tell you to investigate next...


Fingers are crossed...

 

Well, I finished installing the new valve springs today. Used a little higher closed seat pressure (153 lbs) and spring rate (354 lb/in) Comp springs and carefully checked seat height with my nifty new spring height micrometer and set closed height at 1.895 inch. With my spring seat cup and assortment of shims, this is as close to the suggested 1.900 spec as I could get. (Note the shop that assembled the heads for me had their springs at 2.150 inch closed height, so I am sure I lost about 50-60 lbs from their advertised 125 lb seat pressure.) I used new Comp retainers and 10 degree locks, switching from the 7 degree locks and retainers the machine shop used. I also carefully checked clearances on all of the valve guide plates and found one that needed a little adjustment by Dremmel. Then carefully set valve lash on the hydraulic lifters. While I had all of the plugs out, I also re-checked compression- 125 psi plus/minus 1 psi in all cylinders. Re-installed the valve covers, checked all wires for connection and started it up. Started in about 1/2 second. Attempted to re-check ignition timing and found my 45 year old timing light finally died. Rats. Well, timing should be OK, since I did not change anything there- will check later with yet another new tool purchased for this job. Next....Road test. I went to my usual deserted two-lane road and with the car properly warmed up, drove in second gear at about 40 mph and then went WOT (usually this is where the power just died at 4800 rpm) . As I tried to keep an eye on the road, the speedo , the tach and watch for cops, things started to happen really fast. I backed off at about 6000 rpm, since I think I was already going about 80 mph. Holy cat shirt! I think the problem is fixed. When I got home I scheduled dyno time next Monday. I will be curious how much HP the car has, now that it revs the way it should. Will post results. My valve spring pressure gauge should be here tomorrow, so I will also check the actual closed seat pressure.


Thanks to all who offered advice and moral support during this puzzling problem. Lesson learned- always check work done by others, even if the have a good reputation. RA

 

valve seat tool


more careful reading at 160 lbs. Camera in other hand


Moroso valve seat pressure tool

Checked the valve seat closed pressure with my new springs and 1.900 inch target height. Actual installed height is 1.895 inch. Specs for springs state 153 lbs at 1.900 inch. Measured pressure is 160 lbs plus/minus a couple lbs, so right on target. Can't wait for the dyno results.

 

Awesome job man! Glad to hear its fixed. Hopefully the dyno treats you right..

As per our PMs, I've done the valve spring dance several times and I know how tedious it is but....it HAS to be right.

Good job on sticking with it and working through the issue.

Keep us posted on the dyno numbers.. I'm guessing it does 350 rwhp...

 

BTW I've never seen that Moroso valve spring tool that checks pressures with the springs on the head and rocker arms still on, thats a handy tool I wouldn't mind having.

I need to check my spring pressure, (although I'm afraid to know).... I have about 17k miles on my springs now and I'm sure they are ready....