Having trouble getting my rebuilt 455 to generate good power. I thought I was having timing issues, then carb issues, but no, looks like engine vacuum readings indicate something else.

Engine is a 70 455 block with lo-comp pistons (.030), C heads with all new big valves, springs, guides, push rods, rocker arms. W31 cam with all new lifters, timing set, oil pump etc. Carb is built to 70 specs.

Engine has good consistent compression (147-150 lbs.), starts if you barely touch the key, and is not backfiring or dieseling. Is not running hot (so far).

My mechanic who put the vac. gauge on it - why did I not do this myself - says that at idle the gauge is rapidly vibrating between 3 inches up to 10 inches. I've looked on line at all the vacuum gauge charts, and I can't find one that indicates this symptom. The closest I've seen is the one indicating a massive intake or carb leak, but mine is a vibrating reading, not constant. I didn't like the way the valley pan fit when I installed it.

Anyone else had this condition? An help would be much appreciated.

 

Does your gauge act like any of these senarios????
http://www.secondchancegarage.com/public/186.cfm


go thru each choice and see if your gauge matches the actions of any of
these .... Hope this helps diagnose the problem

Nufo(Fred)

 

New rebuild with new cam/lifter/springs? If everything else checks out out and no vacuum leaks, check cam for flat lobed(s).

 

Thanks for the link Fred. I didnt see a scenario like I detailed above. I'm going to put a vacuum gauge on it myself when I get it home and see what readings I get, and how they change over engine speed. I think it's going to be either a manifold leak issue, or possibly a cam to crank timing issue. Anyone knows what the symptoms are of the cam to crank being one tooth off?

 

Bump

Could the above vacuum readings be caused by the cam to crank being literally one tooth off from being correctly aligned?

 

I believe a somewhat easy way to check crank timing is to get #1 piston at Top Dead Center than confirm the timing marks line up at zero degrees.

 

Joe, a couple things...

1. Where are you attaching the gauge
2. Is that a NOS W-31 cam or a regrind
3. Does the car have power brakes
4. Have you pulled any plugs to read them

 

When you say the vacuum gauge is sweeping between 3 and 10 inches; do you mean the 3 and 10 inch marks or a 3 to 10 inch variance from whatever the idle vacuum is. If it is the latter it sounds like a vacuum leak. check around the top of the intake with propane of whatever you like. also block both breather holes on both valve covers with your thumbs to make sure there is no vacuum in the crankcase. this would indicate a vacuum leak on the bottom side of the intake.

 

Have confirmed no. 1 TDC matches 0 deg. on balancer.

 

1. Gauge is getting manifold vac from the intake fitting in front of the carb
2. It is a new cam made by the OE supplier to Olds. Have used another one out of the same lot with zero problems.
3. Yes - just rebuilt by Steve Gregori
4. I've pulled all the plugs to check compression. It ranged from a low of 147 to a high of 151.

Thanks for responding. I'm stumped on this one!

 

I recorded a video of what it's doing. At starting it settled into a high idle (1100 rpm) and showed a vacuum reading of 10 inches with a very slight pulsation- maybe 1 inch pulse. After kicking it down to regular idle at 750 rpm, the needle becomes a blur reading between 2 inches and 8 inches.

The reason I keep mentioning the one tooth thing is that I remember when I was putting the motor together that the timing marks did not exactly align with each other no matter what teeth I indexed on. It wasnt a lot off, but it wasn't exact. I used a Melling select set that has the three keyways on the crank. I for sure used the 0 deg. one.

 

Does it seem to be misfiring? A broken/weak valve spring can give you normal compression readings while cranking and will allow the valve to float with the engine running. I know the valve train components are new, but sometimes new parts fail.

 

1. If the fitting you are referencing is ON the carburetor disregard; however if it is on the intake runner try moving the gauge to a different runner to see how steady it is. OR, UNPLUG the power brake hose and connect there. Just try a different source of manifold vacuum.
2. From what I understand the W-31 cams are lopey at idle...750 rpm with a high duration cam is pretty low idle and can indicate the readings you are having.
3. See question number 1.
4. Did any ONE plug have more oil on it than the others?

I am inclined to think that the engine is lacking performance because you don't have enough compression for that cam...

I am also inclined to think that the low idle rpm combined with that cam is causing the varying vacuum readings. You said it evens out at a higher idle (1,000 rpm +).

 

The W31 cam was for 350 engines, not 455's right? Are you sure you didn't mean W30 cam? Both the 350 W31 (308° cam) and the 455 W30 (328° cam) will run rougher and will not develop the vacuum you need for PB.

 

An easy way to check for vacuum leaks at the carb and intake is to spray carb cleaner around carb and intake while it's running. If the idle speeds up when you are doing this then you've found one of your problems.

 

Yes Al, but you can run it in either engine.

 

Did you ever figure this out?

 

Not yet, but I have eliminated a vacuum leak and the carb as potential culprits. After I got the car back, I hooked it to a GOOD vacuum gauge off a centrally mounted vacuum port and found the reading is still bad, but not what the shop made it out to be. The vacuum level, at idle is more like 10 inches, and the needle flutters irregularly from about 9 inches to 13 inches. I've got one more thing to do before degreeing the cam and that's to pull off the valve cover and see if I have any installed valve stem height issues, or if the pushrods are all the correct, same length.

These "C" heads originally had the small valves. I had the machine shop install the bigger ones, and I'm hoping they botched the seat cutting and I didnt notice it while putting the motor together - this would be much preferable to having to pull the motor to change the cam/crank relationship.

 

I know what you mean! I'm pretty sure if the cam timing was off a tooth in either direction the vacuum reading would be steady but low, If the engine started at all. I think you are on the right track looking at the valvetrain. Usually large needle movments on the vacuum gauge indicate an intake valve problem, a small nibble on the needle indicates exhaust valve trouble.

 

The plot thickens. Pulled the driver's side valve cover off this evening. Laid a true straight edge across the top of the tips, and the two valves on the ends of the head (one each of 2 and 8) are low about .014 at the tip from the other valves. I don't know if this is significant enough to be causing my problems, and haven't yet figured out if those two valves' assembled height is too low, or if all the other ones are too high.

 

Try pushing each valve down by hand - lets you know if a spring is weak or broke.
Next step, for me, would be a compression test.

 

sounds like the vac gauge doesn't know what to do. most cylinders creating a vaccuum and possibly two cylinders applying pressure to the gauge. follow the bouncing ball. Poor gauge.... it's gotta be really confused... you get my point Costpenn. I think you found your culprit. Two valves not closing all the way....


Nufo(Fred)

P.S. this is an almost totally unprofessional assesment.

 

Trying one last thing before pulling the motor. Does anyone have the spec let's say for a 68 W-30 using the 402194 cam (308 duration) that is detailed in the CSM for when you are checking valve timing without pulling the cover? It's the procedure you do on the #4 cylinder by measuring the height of the intake pushrods at two different places in the cycle.

 

Subscribed

 

Latest update:

Bought the Mondello installed valve height gauge and all valves check within spec. Did not mallet test the springs, but didn't see anything obviously wrong. Did the CSM test on the intake pushrod travel length and

Travel difference between two readings should be .210
Travel difference between two readings actual was .075

Even allowing for the +/- .030 tolerance specified in the CSM, there's a problem.

Will pull the fan and pump off and attempt to degree the cam to confirm, but I think it's pretty certain to be a timing set issue.

Is it worth it to pull the radiator and front end off the motor and drop the pan to fix this without pulling the engine out of the car? I really dont want to pull the whole motor.

 

I am a rank amatuer but w incorrect travel how will degreing the cam help wouldnt it be more likely to be a wiped lobe ???

 

I'm going to degree the cam as a check to the test I did on the pushrod travel. I'm pretty sure the issue is the cam is not opening and closing the valves at the right times because they are not timed correctly due to crappy timing gear mark placement.

 

Joe, the issue I have is trying not to scratch paint while working on the motor, I say pull it out. Also, I'm wondering if the W30 cam is suitable with your compression?

 

Wow!!! this thread is convincing me that I need to buy more measurment tools before I assemble my engine.

 

So what's the verdict? Flat cam lobe?

 

 

Gary,

A few weeks ago, we did the CSM test on #4 intake pushrod. The travel should have been around .200 between the measuring points. Turned out to be only .075. It might be a flat cam issue, but with all the other clues listed above I'm pretty sure it is a cam to crank timing issue. Anyway, I'm going to pull the front of the motor off when I get back from our Zone show and do an in depth degreeing of the cam and will advise as to the results.

 

Degreeing the cam should always be done during engine assembly.

Before going thru all that, though maybe try 2 things

1) retorque all the intake to head bolts. Go 'round 3-4 times.

2) advance the timing a little. Worked wonders on the high compression 403 I was working on last year.

"I am also inclined to think that the low idle rpm combined with that cam is causing the varying vacuum readings. You said it evens out at a higher idle (1,000 rpm +)."

This leads me to believe you need more timing. When the idle is higher, the MA system is advancing the timing and the engine is much happier.

I ended up with VA hooked to the manifold vacuum, so the initial was set back for easy starting, then when it starts, the timing advances quite a lot, and the MA then adds more with RPM increases. The MA had to be modified to suit, and the VA canister replaced with travel-limited aftermarket unit dialed down to ~10 degrees.

Non-stock compression and cam and whatnot required non-stock timing curves to match.

Much happier now. With stock curves and settings, below ~800 rpm, the idle would just deteriorate to crap and then stall. Low vacuum was allowing the power piston to richen the mixture, which only made things worse.

You may find that securing the intake and advancing the timing will cure your ills.

 

Not trying to hi-jack, have a similar issue with a new build 455, if I set the timing to 10-12 degrees it will crank to slow and not start, any ideas?

 

Thanks Chris, but I've tried the retorquing together with spray ether testing, no difference. And, I've tried every possible initial and secondary ignition timing combo under the sun with no improvement.

By the way, that intake nipple you sold me for converting my iron intake over to a correct 72 455 MT design worked out great!!!

 

" Carb is built to 70 specs" which 70 specs? The W-30 and 31 cams used a special calibration in the Q-jet to work with the long .050 duration. Let me know if you need me to look at your carb.

Danny

 

Costpenn, I've been following your thread intently. Is there any progress on your vacuum readings and performance issues?

Chris

 

Can we still find NOS cams??? I really want to throw a NOS cutlass 's' cam in my cutlass whenever i rebuild it. I'm not looking for power, if i wanted power i'd throw in a 455

 

Tony maybe cutlassfi might have an NOS cam. He is the cam man on here and a cam grinder, he may have some originals that he uses for templates.

 

He should be able to make one - drop him a note.

- Eric