Olds/uk455

Hi guys,have a problem with my rebuilt 455 that is driving me mad !
Short story - engine will idle and rev up ok but as soon as you lift off after revving it the engine cuts out

Longer story - I rebuilt my 455 some time back to go in my Bullnose Firebird from parts from two 455 engines,Used block from a 76 engine with the nodular crank,rods,Ga heads and intake manifold from a 72 engine.
Had block bored +30 thou,fitted silverlite higher compression pistons,had parts balanced. Fitted Comp Cams K kit parts
https://www.summitracing.com/int/parts/cca-k42-222-4
XE262H Camshaft,fitted timing gear straight up on the O mark (didn't degree cam) new HEI dizzy,leads etc and a rebuilt Rochester Quadrajet carb. Also fitted adjustable roller tipped rocker arm kit
During cam break in engine fired up ok but did overheat towards end of break in period as brand new thermostat didn't open ! Used high zinc break in oil during cam break in. Removed this oil and cut open oil filter after break in - all clean,no trace of metal. Refilled with high zinc oil and engine still ran ok. Then refitted inner valve springs that were removed for cam break in period and reset valve lash. Since then have had this problem of engine cutting out after you rev it. Have reset valve lash twice since then but no better. Since this problem started have fitted vacuum gauge - only have 11" vacuum at idle which seems a tad low for this fairly mild cam ? Have checked for vacuum leaks using smoke test and propane run around all gaskets etc,no leaks found. Even changed the turkey tray intake manifold gasket for thicker composite ones fitted with VHT copper gasket cement - no better. Compression test - all cylinders within 10psi of each other with all adjacent cylinders within 5psi of each other,all between 185psi and 195psi. Engine still only has few hours running time on it as car it's in isn't ready for the road yet.
Can't get engine to idle smoothly either ,revs go up and down a bit all the time.Revs also do same if you hold revs at around 2500rpm.
Have tried four sets of spark plugs gapped between 40 and 60 thou,no better. Have tried a known good HEI dizzy cap and ht leads out of the 403 Olds in my TransAm on the 455,no better.
Timing chain aligning marks haven't moved as whipped front cover off for a look see. Have tried varying ignition timing,currently at 22btdc at idle,no change,engine still cuts out after you rev it.
Even thought it might be carb problem so fitted Fitech Fuel injection to it,no better,exactly the same problem !
Engine now fires up instantly from cold with the Fitech fitted almost before you turn the key to the start position,so am guessing the fuel and electrical systems must be pretty spot on but engine still has low vacuum at idle,uneven idle and cuts out after you rev it.
Engine does rev up very freely though without hesitation.
Am thinking it must be mechanical problem but what ?
Have done another oil and filter change since break in,again cutting filter open,but no sign of any metal,debris or sludge so don't think any cam lobes have worn down. Cam lobes also all looked ok when I removed intake to fit composite gaskets.
So guys,before I remove intake,valve covers and maybe water pump and front cover to investigate further have any of you got any other ideas of what's causing engine to run like this ?
PS - no oil in coolant or coolant in oil and rad hoses dont pressurise so am guessing head gaskets are still ok
Apologies for length of post but the thing is doing my head in !

VC455

You've looked very thoroughly at most problem areas.

What is your total timing and all in at what RPM?

How many degrees of vacuum advance at what vacuum?

Olds/uk455

PS - have even removed each plug lead one at a time with engine idling and revs drop the same amount each time.
Oh and I swapped the entire HEI distributor plus cap and leads from the 403 Olds not just the cap and leads - no change.
Am considering stripping engine down to have a proper look at condition of cam and lifters

Olds/uk455

Last time I checked it had all initial and centrifugal advance in by 2800rpm ish with vac advance plugged,think it was around 34 degrees all in then
Don't know how many degrees of vac advance. Have tried running it with no vac advance and with canister connected to ported and full manifold vacuum. No change,still runs enevenly and cuts out after you rev it.
Still think only having 11" of vacuum at idle with this fairly mild cam is too low.
The mild cam in the 403Olds in my 79 TransAm gives 20" of vacuum at idle

oldcutlass

There was a member here that had similar problems and it turned out he aligned the wrong marks on the timing gear. The only other thing that would come to mind is too much rocker preload.

Olds/uk455

Ah,guess as it ran ok when I first fired it up to break in cam with inner valve springs removed and the fact that the timing marks on crank and cam sprockets still line up now the timing gear is still aligned ok.
Prob only started after I refitted inner valve springs,which was either just a coincidence,or maybe I do still have some of the rockers with too much preload.
Did wonder if this was the cause which is why i've reset preload again since I refitted inner valve springs. But maybe I still have them set too tight.
Would too much rocker preload cause my low vacuum at idle ?


Here's pic of timing gear taken since problem started. Still in same positions as when I first built engine when it ran ok during cam break in

VC455

Too much preload will not allow the valve to close completely, which could explain your problem

Olds/uk455

Ok guys,what's the best way to adjust preload then ? Have adjustable roller tipped rockers fitted. Should I again follow the method given by Comp Cams ?
Which looks like hasn't worked the last couple of times if valve lash is indeed still too tight.
Or shall I try setting valve lash with engine running ? Do have an old pair of valve covers I can cut a section out of their tops so I can run engine without squirting oil everywhere.
If I do the engine running method how much should I tighten them after they start ticking when loosened ?

oldcutlass

This is the clean method:
http://www.hotrod.com/articles/ccrp-0702-camshaft/

With engine running method:
What I do is warm the engine to full operating temp first. Then pull the valve cover and do one bank at a time. Loosen until it starts to clack, slowly tighten until it stops, then give 1/2 turn and lock it down. Move from rocker to rocker, front to back. (Note, som cam manufacturers recommend from 1/4 turn to 3/4.

Olds/uk455

Thanks for that. Think i'll give the engine running method a go,hopefully some time during the next week or so.
Will post on here whether doing this cures my uneven running,low vacuum at idle and cutting out after revving engine. Fingers crossed it will

TripDeuces

What about the dash pot?

Olds/uk455

Have only just had time to start looking at the 455.
Decided to remove intake and camshaft oil splash shield to have a look at lobes of camshaft.
Def no intake leaks at intake gaskets when I removed them by the way.

All camshaft lobes look ok and all lobes have same wear pattern.
Does wear pattern look ok to you guys ?
Will remove valve covers when I get time and reset preload

Olds/uk455

Thinking too tight preload on valves might be causing my problems reset valve lash on all valves half a turn past when pushrod stops going up and down
(basically setting them half a turn looser than Comp Cams lifter paperwork said do )
Just fired it up - no change. Still uneven idle,low vacuum at idle and engine cuts out after you rev it.
This problem only started after I refitted the inner valve springs after camshaft break in,ie,all I changed from when engine was running ok was I added the inner valve springs that came in the Comp Cams K kit and reset the valve lash.
As it doesn't seem to be a valve lash adjustment problem,could it be that the inner valve springs are too strong ?
Would having too strong valve springs fitted cause these engine running problems ?
Am thinking my next move is to remove these inner valve springs and fire up engine with just the outer springs fitted,like when it ran ok during cam break in,and see if it runs ok then.
Am running out of ideas as to what else to try