xceleratemaroq

push rod's to long not alowing the valves to close all the way.. esp exhast valves i would inspect that if you installed a diffrent rocker arm or thicker head gaskit this could be your problem..

Saabster

iTrader: (2)

I personally keep coming back to the rocker arms. If I were to take a stab at it I'd say you have a couple lifters that are pumping up. Just my guess I suppose, good luck man.

five7kid

iTrader: (14)

How would too-long of pushrods keep the valves from closing? Longer pushrods, the rockers would be farther up the studs when adjusted, that's all. Geometry might not be ideal, but that won't keep the valves from closing.

Lifters don't "pump up" at idle RPMs.

Gummy valve stems is a possibility, but still doesn't sound very likely.

Saabster

iTrader: (2)

Well if they were way too long, the lifters wouldn't be able to adjust down far enough and would hold the valves open. That doesn't quite explain how they were fine before storage and are now too long.

Yeah, not very likely I suppose. I was thinking more that they were jammed fully extended for some reason.

xceleratemaroq

i was under the impression that some engine work was done.. like replace the cyl head's just trying to help.. i would remove the rocker arms and use a dead blow hammer and tap the valves down look for a valve that is "sticking" or not returning as quickly ie.. bent valve.. i belive that is where your problem lie's

lewandom

is it poss. the timing chain skiped a few teeth???

DNSTA

All very good suggestions but if you read the whole post you will see that none of them apply. The problem was present before the engine was taken apart to find the problem. Heads, rockers, gaskets, timing chain, cam, pushrods, all the same. The engine ran last year and now it doesn't. Changes were electrical and exhaust both of which have been ruled out.

A bent valve is not the problem. Heads have been off and inspected. I know we missed something. Now to find out what.....

Soon....

DNSTA

Ok, finally an update. I'll be pulling the engine and getting it on the engine dyno this Saturday. I'm not sure we'll have time to start diagnosing the problem but at least we'll have it out and ready to go.

DNSTA

Motor out and on the dyno. We didn't have time to do anythign to it yet but at least there's some progress. Maybe some time this week we'll get it running enough to start figuring out the problem.

DNSTA

Sorry about the long delay in updating the thread. Here's what's going on now.

I finally got some time to get to the dyno shop and get things going. (Actually, I had to take vacation time to do it but...) Anyway, we got the motor on the engine dyno and got everything hooked up. Remember, the reason we're doing this is to verify that the car, (wiring, fuel system, accessories) were not causing the off-idle bog.

We got it fired up and got everything tuned perfectly. Cracked the throttle and.... NO! STILL THERE!! It's slight but still completely unacceptable for a car that's supposed to go down the drag strip. Plus it didn't do it last year so what the hell.

So we're kind of back to square one. We defiantly know what it isn't. It's not the fuel system, the electrical system, the carb, or any type of drag from the transmission or the accessories. That leaves what? The internals and the valve train.

We had it apart before it went on the dyno so we know the crank, rods, and pistons are good. The heads have no crack, compression is beautiful (~270 psi average per cylinder) and the leak-down test showed an average of 3%. Looks great!

So now were left with valve train right? Cam? Lifters? Pushrods? Rockers? Springs?

We pulled the cam and put it on v-blocks to measure the lobes to verify we didn't wipe any and it was fine. We then rolled and measured the pushrods on the v-blocks and found nothing out of the ordinary.

I guess that leaves the rockers, the lifters, and the springs. Weak springs could cause it but they're brand new Comp pieces with less than 1,000 miles on them. The lifters are also new Comp roller conversion pieces so replacing one at a time is not an option.

Give me ideas!! I need help and apparently so does the owner of the shop.

hectre13

iTrader: (4)

who knows.. maybe defective springs :\

DNSTA

They're coming off in a few days and going to a shop that has a spring rate machine. We'll see if anything is out of whack. How bad would they have to be? 10%-20% from advertised rate?

sweetaq

iTrader: (1)

Could someone please tell me how this can not be a ignition problem. A bad connection in the coil or something or a bad distributor? You guys seem way more experienced than me by a long shot so I am just wondering how this isn't being brought up more. With the exception of the wierd *** loosen the rockers thing could a bad ignition cause these issues.

Could a bad connection or too much resistance cause the spark to be delivered late and there for retarded?

naf

iTrader: (7)

Any difference in charge speed due to resistance or reduced current is going to be several orders of magnitude below anything we could measure with a timing gun. We can assume that the speed remains constant or that increased resistance will not retard timing.

DNSTA

It's not an ignition issue. The problem exists with two sets of plugs, two sets of wires, two dizzys, and three coils. This work is being done in a fully equipped shop. We have the car on an engine dyno with a snap-on scanner on it for the ignition at all times. We even went so far as to remove the plug wire from one cylinder at a time to see if maybe one cylinder was causing the problem. The test was inconclusive but the fact remains that we are quite thorough in our testing unfortunately we aren't coming up with anything.

Back to my last question though. What's everybody’s thoughts about the springs?

jjlabinski

This may or may not have any bearing on your situation but I wanted to share with you the fact that I wiped out a brand new valve train on a 10,000 engine with less than 4 hrs running time due to those piece of **** comp cams retro fit lifters with link bars.

DNSTA

The cam has been taken out and checked on v-blocks. It's fine.

Back to the springs question. Anybody? five7kid?

DNSTA

bump for help.....

sgreen3

iTrader: (4)

could be bad valve guides, bad guides can cause real low vacuum.

DNSTA

Sorry, forgot to put that piece in. After the removed the cam and checked it and put it back in we regained our vacuum, or at least most of it. The guides seems to be just fine. Thanks for the idea though.

I need a Dr. House. He mas be an *** but he's always right.

sweetaq

iTrader: (1)

yeah but house isn't right until after he has tried 27 different theories first, sound familiar? LOL

DNSTA

Very good point! I believe I'm just about there.

DNSTA

Still in need of some help....

DNSTA

Please. Someone help me get this car on the road before it snows!

CamarosRUS

Sorry man this sucks royally.


After reading through (I am NO expert) it could possibly be some shitty lifters....do you have access another known working set you can try to throw in there.

Have you run the motor with the valve covers off to actually see the rocker action?


Triple check the timing set is lined up properly and check those valve springs to make sure they are all up to snuff. Can't tell you what snuff is but knowing what they should be and what they are; I'm sure you could infer for yourself.

jjlabinski

I suggested a while back to suspect your lifters and I am going to hold to that premise.

Have you entertained the idea of your timing set actually being a "set" and that a gear from another set wasnt used inadvertently?

Again on those lifters mine hung up in the lifter bores while the engine was running causing the same condition you described before wiping out the cam.

86LG4Bird

iTrader: (1)

Sorry for a late response here, but I just now noticed this thread.
"~270 psi average per cylinder" sounds very high. I know it's almost a 12:1 motor, but that would be a very small cam to make that cranking compression. And your previous mph doesn't suggest you're running such a small cam.
Have you re-degreed the cam since the problem started? It appears that it's overly advanced to give such a high cranking pressure. I know you may think it would only be retarded if it jumped a tooth or two, but it's just as likely to jump the other way with a kickback at an attempted start or at shutdown (times when any slack in the chain is being whipped).

DNSTA

Thank you everyone for your responses. We have still not been able to identify the issue. I am leaning towards the lifter as well but need to collect the funds for a replacement set as they are not cheap.

86LG4Bird - The compression is closer to 13:1 ;-). The cam has indeed been re-degreed and a brand new timing set is being used. The cam is indeed very small. The main focus on the build was streetability and we most definitely achieved that. The MPH is most likely due to the 4:11 gears and the gobs of low end torque.

Here are the cam specs:

Camshaft Part # 12-422-8 Grind # XR270HR-10
Duration @ 0.006": 270° / 276° Duration @ 0.050": 218° / 224°
Max Lift w/ 1.5RR: .495" / .502" Lobe Separation: 110°
Lobe ID#'s: 3313 / 3314 Intake Centerline: 106°

Ryan3834me

I know it was 4 years ago... Did you ever resolve this?