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Closed38 replies

351C trouble.

G Guest
I am experienceing some trouble with my newly rebuilt 351C 4V engine.

For some strange reason i get backfires thru the carb once the engine reaches normal operating temp. and the engine starts to feel very weak when i drive the car...when this occurs i just shut it off.

First i thought that it was an ignintion related problem but after doing all the tweeks in the book with no results we started looking at the valve adjustment.

The valve adjustment was done after Cranecams specs. with the new lifters installed zero lash and then 1/2 to 3/4 turn on the rockernut. Anyway now to the strange part. A bickfire thru the carb would suggest that one or more of the intake valves doesnt close properly right ?
But when i remove the valve covers after i have warmed the engine up to operating temperature the rockerarms are so loose that i can lift them out of position and even remove the lashcaps on the valvestems...realy strange.

And since the rockers are this loose i cant understand how the valves could fail to close since the rockers barely is able to open them with this loose adjustment.

Now we have tried to set the valve lash both the slow way by turning the crank and adjusting the and also the messy way with valvecovers removed with no luck.

On thing that i also is confused by is that the "springy" feeling that the lifters had when i installd them seems to be gone and the lifters feel "solid" even though the valve is in non-lift and the rocker is very loose.

I know that the backfire is somehow related the the valves but not how..so if someone could shed some light on this i'd be more than happy....summer is slipping away.


My engine combination looks like this:

351C Block
4V Open chamber with 2V valves "mildy ported"
Compcams 305H cam 0.585 lift int & exh
Compcams matching springs % anti pumpup hydraulic lifters.
351C stock Crank
351C stock connecting rods
Speedpro Flattop Pistons
Hastings cast iron rings
Crancams guideplate pushrod kit.
Harland Sharp roller rockers
Ferrera Stainless valves
Edelbrock Torker II intake
Barry�grant SpeedDemon Carb
MSD Billet distributor
MSD Blaster 2 Coil
MSD 6AL ignition control

/Jonas W
Original Post

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H hemip (Guest)
Wonderful, i see we have another Swede here!
Alright, backfire throught the carb is a LEAN condition. Backfire throught the exhaust is a rich condition. Naturally, some other faults may show the same effect.
Set the lasch to zero and 3/4 more turn. The 351C has pedestals, so this type of adjustments is not possible. But imagine it to be so when thightened to the pedestals.
If not, the pushrods is the wrong lenght.
Goran Malmberg
S Soulcollector (Guest)
Hi All !

Thanks for your replys.

( Hej G�ran kul att man inte �r ensam svensk h�r ! )

I might not have been clear enouch in my post so i'll try to clearify the problem.

The carb is not to lean as i get a slight blackish exhaust while reving the engine the carb is a brand new Speed Demon 750 and we have tried to alter the mixture back and forth with no result either.

The valvetrain has been alterd from the original pedestal design to adjustable roller rockers by the crane cam conversion kit.

Now here's a picture showing how loose the rockers are just after the valvecovers are removed with and engine at operating temperature. http://www.realvis.com/jonte/looserockers.jpg

Forest: Interesting that you write that the backfire can be caused by the exhaust valve not opening. When we had the valvecovers of and did the adjustment we could hear how it was popping back thru the carb while cranking it without the coil attached. then we started tightening the exhaust valves down a bit and the pops disappeared.
But since it was impossible to say wich of the rockers that rattled i can't say that adjusting the valve-lash while the engine runs is a very good solution but then again i cant adjust it with the engine of either since the spring action in the lifter just isn't there anymore or at least not on all of the lifters.

Anyway what i don't understand is if the rockers could be this loose or if there is something that just dont work as it should...and if the backfires now comes from a non-opening exhaust valve why does this occur...sudden drop in oilpressure or some other variation that takes place once the oil temperature rises higher.

I started reading on other forums too and saw that some people had problems with the cam-lobes beeing grinded down...This sounds unlikely since the cam,lifters,pushrods and other valvetrain parts are brand new and installed by the book. and broken in over a period of 20 minutes as specified.

Here's a picture of the whole machinery. http://www.soulcollector.se/nemesis/jpg/panterastuff/351cEngineInstalled01.jpg
forestgforestgMember
I'm not sure I want to try to explain why non opening exhaust valve causes popping back through the carb because I would probably be wrong and everyone would feel obligated to waste a bunch of bandwidth pointing out why I was wrong. The reason I noted that it can happen is that I noticed it happening on my trans am when an exhaust lobe went flat. I believe it has to do with pressure being trapped due to exhaust not opening and then relieveing into the intake when the intake opens.
C charliemccallMember
I don't know how the rockers could get that loose.... I'm sort of with Ron - are you sure that you are preloading them while on the flat part of the cam? If you are preloading the rockers while on the "hump" of the cam, then as it comes around to zero lift you'll end up with a lot of slack.

You could also get a lot of slack if you've bent a pushrod... Take a loose valve and doublecheck that you haven't bent a pushrod?

------------------
Charlie McCall
1985 DeTomaso Pantera GT5-S #9375
"Raising Pantera Awareness across Europe"
http://briefcase.yahoo.com/gt5s_1985
S Soulcollector (Guest)
Charlie: Yes the method i used for the adjustment is the very same as Crane suggests and exacty as Mike Dailey does on hit web site. http://www.panteraplace.com/page131.htm

In fact i have the exact same lifters that he installs on that website of his and he also uses the crane adjustabe valvetrain conversion.

I am going to florida next week and i'll try to get in touch with compcams over there and sort out what the heck is going on with my valvetrain.

How tight should the rockers be when you turn off the engine and remove the valvecovers...should they be loose at all when not in lift or does the plunger in the lifter bottom out over time after the oil pressure goes away and that's why the slack occurs ?

Anyway to me it seems a bit dangerous that the rockers are that loose at any time since let's say i go on a ferry that vibrates quite a bit the rockers might get dislocated and crack !!! when the engine is started again. Something must be wrong with either the cam , lifters or both.

I read on another forum that if something goes wrong with the lifters during the breakin period the cam lobes can go flat in 15 minutes wich in my case would explain why the rockers seem to get more and more loose if it's that way i guess i will have a 0.050 max lift pretty soon.
S Soulcollector (Guest)
G�ran: The lash seems to stay the same even if i check it the next day. I thought that i could get that springloaded feeling in the lifter back and re-set the lifters but that does not seem to work.. my lifters feels solid now no matter how long i wait.

Ill tear the intake off and have a look at the lifters and an also check if the cam has been damaged by this...I guess that the easiest way of checking the camlobes is to place a dial indicator on the edge of the lifter and then make it "zero" when the lifter is on the heel.

To me this whole problem seems as if the plunger is stuck in the bottom of the lifter at all times until it randomly gets released by heat,vibration and or increased oil pressure.


[This message has been edited by Soulcollector (edited 07-16-2004).]
P paulvMember
I have the same set up, and had the same problem on a couple of valves when I first started the engine. What happened on mine was the rocker studs started to back out of the head, opening up the clearance. The directions state that the studs need to go into a CLEAN, DRY hole, use Loctite and propery torque them. I had a couple back out slightly, causing extra cleance. This might be the problem. Good luck.
Paul #3040
marlinjackmarlinjackThe Machinist #5723 AMARGOSA MACHINE 'Running on Empty- Middle of Nowhere'
Soul!... A couple of things come to mind: 1. Did you 'pre-lube' the Hydraulic lifters before installing them, by pumping oil in the side holes with and oil pumper can?. 2. Could you be adjusting the valves 360 Degrees 'OFF' from the 'True' Top Dead Center (both Cylinder #1 Valves are on the lobe 'heels'); So that you have started adjusting the valves on the TDC of the Exhaust stroke; which is incorrect? 3. I do not think it is correct to adjust the lash on Hydraulic lifters, While the engine is running, as with Mechanical Lifters. 4. On your 'Poly-Locks', you MUST tighten BOTH the Poly-Lock AND it's SET SCREW simultaniously!! Or they will never stay locked, and will back-off. 5. If you have lost the "Springy" feel in the lifters; they have either, NOT 'Pressurized' properly(see #1) or they have collapsed. 6. If you DID NOT completely cover the Cam and lifters with Moly-Disulfide or other 'Break-In' lube; and then run your Engine, on it's initial start-up, at 2500 RPM for at least 20 minutes; Then you have destroyed your cam lobes. Good-Luck with it! Regards, Marlin.
bosswrenchbosswrenchMember
A few things come to mind:
first, spinning the pushrod between thumb & finger while tightening to find zero-lash often doesn't work on fast0bleed lifters (especially new ones empty of oil) because the bleed passage removes most of the normal resistence when you get to zero lash. A modified method is to slightly lift up as lash is reduced until no motion can bes detected. I always hot-adjust lifters (both solid & hydraulic) with the engine running, anyway.
2)- popping thru the carb indicates an intake valve problem, going lean etc Theres no connection between the carb & exhaust unless BOTH valves are hing open. Exhaust pops are heard in the headers.
3)- with roller rockerarms, its possible to install them with the rocker shaft upside down so the flat nut-relief is down toward the stud and the round section is upward. Adjustments will not stay locked in this position.
4)- its also possible to put a pushrod on the edge of the lifter seat and go thru the wholer exercise. Then when you start the engine, the pushrod normally drops to the seat and you got 1/4" clearance on that valve....
Finally, "springy" lifters usually don't have oil in them. Ones that feel solid are obviously full, which is as it should be after firing the engine.
S Soulcollector (Guest)
Thanks for all your replys.


We removed the intake today and the sight was unplesant to say the least. We managed to remove all but 7 lifters the right way and one of them had been chewed down almost 1/4" and that lifter was the only one that the plunger spring still worked in...The cam looked OK on a couple of lobes but all of the lifters was worn in one way or another ?!

Bad cam cast ?

All brand new parts $2000 wrecked in 30minutes.
I'll get in touch with JEGS and Compcams and discuss this. Everything has been assembled based on their instructions. But as usual i'll probably get no compensation from Compcams or JEGS.

How should i proceed...i assume that i need to take the whole thing apart and flush it so i get rid of all the metallic debris ?

PS. I'll post pictures of this nightmare later on..right now i'm busy removing the engine and taking it apart..AGAIN !!! Douh !

Thanks
/Jonas

[This message has been edited by Soulcollector (edited 07-18-2004).]
bosswrenchbosswrenchMember
In your original paets list, you mentioned a bunch of aftermarket parts. By chance was not mentioned an oil restrictor kit? Because the restrictor kits go into the main bearing-to-cam bearing passsages and one is provided to restrict oil to one bank of lifters.... IF you're running a solid lifter cam. If you're running hydraulics, especially fast-bleed hydraulic lifters, you leave that restrictor out. Otherwise, oil starvation will occur to all the left-side lifters.Nothing's free, you know- fast-bleeds use more oil than normal hydraulics. Distasteful though it may be right now, I would totally disassemble the engine and scrub it clean. First, you need to catalgue all the stuff thats wwasted. Second, all that iron went somewhere and is likely just waiting for a chance to pop out in your new motor. Don't be like the racer that blew up seven (7.0) engines in a row in his stock-car by re-using the same not-too-clean baffled pan & oil cooler after each blow-up.
S Soulcollector (Guest)
I did not install a restrictor kit as i had read about the oil-pressure issues that came with it. The lifters are the standard comp-cams 832-16 wich they recomend. and not the fastbleed premium that they also offer..

Anyway i'll get on with the teardown now so that i might get to have a ride in it before the snow starts falling.

PS. Any good tips on speedshops in florida...i'm on my way to miami and i will spend some time shopping too.
H hemip (Guest)
I dont think there is any material or cam fabrication problems. More likley as what Jack says. OR, something with the break in.
One may scuff hte brake in lube away from the lifters by to loong cranking period of the starter. Then if the rpm dont raise to 2000, becouse of idle afjustments on the new carb,the situation become even worse.

THE FIRST COUPPLE OF REVELUTION IS MOST IMPORTANT.

Here the cam lube makes its work, but not for very long if the engine dont fire up.

Goran Malmberg

[This message has been edited by hemip (edited 07-19-2004).]
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