SBC timing issue

[madmooney]

Hello all. I have a new 388 sbc scat 6" bottom end,DSS flat tops, Profiler 64/195's and a Howards 110981-08 HFT cam. I let the mach shop assemble
the shortblock. So I get it home and start to put it together and notice the cam is in straight up ( I asked for +4 ). OK I thought we'll see how it runs.
Get it in the truck drop the dizzy in at 6 before and it won't start and acts like it wants more timing. So we pull the dizzy and give it another notch
on the gear, motor then lights up and cam break in proceeds with no issues sounds good no heating ect. Shut down and inspect for leaks and
when we try to restart it kicks back and won't start, back off timing it fires up drive around block revs ok seems down on torque. Won't start the
next morning kicks back and blows the gear off the starter. Ok so I go to starter store and return with the mondo geardrive starter, this starts it.
By now I'm freaking out as we've timed a million sbc's with a vac gauge and never had a problem so I put my old timing light on it and it says
30 before! I go get my buddy with his good timing light and it reads the same. The camshaft has to be really off for this to happen,Right? What if they
installed the crankshaft gear @ 4+ and installed the chain & cam gear straight up could it cause this? I did not check the key index at the crank. I'll
be taking it back apart as soon as I can get some help or my sore back allows. Anyone have any ideas about or seen this before? Thanks in advance
for any replies.

[bobmc]

do a cranking compression test before tearing down, as I understand you have the initial timing at 30 deg? turn it back to maybe 22 deg

[Baprace]

madmooney, you are confusing cam timing with ignition timing, your cam may well be advanced like you wanted regardless what bushing you found , I like initial ignition timing around 20 - 24* initial and with not having any experiance with your cyl head I would start at 34* total timing, some heads want more and some want less timing, depends on the spark plug location and the fuel being used. The torque may feel less than a stock cam at low rpm's but you are not racing at low rpm's some BIG cams don't make any power until the engine is at 4000 + rpm's. Don't panic until you have some time on the combination , then you may notice that the fuel jetting is a tad off , torque converter is a little tight , the rear gear may not be exactly what is needed. Keep us posted on your updates and let the members help you get that beast running.


bobmc , understands what you need for a decent starting point.

[steve cowan]

Can the machine shop tell you what centreline they put cam in at ??
The spec recommends in at 104 icl
Cannot just assume to put it in at 4 advance
I have had timing sets go in-2 to get advised ICL of 104 -108 as an example.
Did you set total timing when doing cam breakin?? Total around 32-34 is where i would be shooting for.

[Geoff2]

Most shelf ground cams have 3-5* of advance ground into them. So if all the machining was in spec & the cam installed 'dot to dot', then the cam is advanced as you wanted.
As far as idling etc, that cam is probably going to want AT LEAST 30* of timing at idle for best idle quality. So not surprised that more timing was needed to get it to idle well.

[BillK]

Something that nobody else has asked is ..... are you running a vacuum advance distributor ? I personally dont think you can run most engines on the street without it.

[madmooney]

I was shooting for +8* cam to crank (cam advanced) as this was where the 360 with Howards 110971 (5* less duration than current) that
we just took out of the truck ran best at. The 30* reading is at 8-900 rpm no vac advance if you back it off to 18-20* it acts retarded
and dies won't start/backfires. It would like to idle closer to 40-45* but kicks back and won't start there. have not heard any pinging or
other weird noises, plugs appear normal if kinda rich as carbs are not tuned. Only gonna pull timing cover and oil pan at this point to
degree cam and check rod bearings.

[jeff swisher]

Large runner heads with a weak carb signal and large overlap cams will like a lot of idle timing.

You know that probably.
Here is something you really need to check for the starter kick back issues you are having.

I have seen this a few times.
After you shut off the running engine i have seen the rocker arms all get pushed back up and pushrods get pushed into the lifters this happened with lifters that could not handle the valve spring pressures.
I have seen it with 110 seat pressure Z springs and generic hydraulic lifters.

Pull a valve cover and crank the engine over ...It does not need to start ...then sit for a few seconds and watch the rockers and valves..
Are the valves slowly closing???

If yes you have an issue that can be fixed easily.

Hook a kill switch to negative or positive side of coil.. Kill the power to the coil and crank the engine over with the key for about 3 seconds then flip the switch to allow power to the coil.

No more starter kick back and she should bust right off.

If you are setting timing to 30 and it jumps to 70 before without you doing anything you could have another issue I have seen.
That issue was the distributor was not siting deep enough.
I had to remove material off the base where the distributor gasket goes.

You did not mention that issue though.

Even if the valves are not closing after you turn the engine off you could possibly fix the kick back issues with the kill switch.

[Ericnova]

I can't restrain myself and just have to ask...Why THAT cam choice??

You got what appears to be a really nice short block, with a pretty darn good cylinder head on it, picked a cam with 241° @.050 duration...but a paltry .470 lift??
You are leaving so much of those heads potential out of the picture with that no lift cam.

Just curious to know why you picked that cam. Using 1.8 ratio rockers or something??

[F-BIRD'88]

This cam will want at least 26 deg base timing at idle
(short 10 deg mech adv curve) 26+10=36
It may well run best with the diz mech advance curve locked out.. Locked timing 34-36 btdc.. Then 10-12 deg vacuum advance using ported vacuum on the carb.

If you are not willing to accurately degree the cam in don't bother moving . it.. Multi keyway crank gears are notoriously wacked out..
Bad cam choice for a hotrodded truck any way.

Much better hot truck hyd cam
Isky 201274 274 Mega Cam 274 226 108 (104/112) .490"

[gmrocket]

Sounds like your dizzy needs correct phasing. If it’s off, it could fire another plug and cause your hard start or backfire problems

Where The cam is degree’d at doesn’t screw up your dist timing.

[rebelrouser]

Quick way to check the cam timing. Roll the engine to tdc on the overlap, measure the rocker arms,one exhaust is closing,intake is opening, if the cam is heads up, the rocker arms will be same height. If the cam is advanced the intake rocker will be open more than the exhaust. I would check your cranking compression just to see how much pressure you are trying to start. That may be the root of your problem.

[madmooney]

Hello all and thanks for the replies. Jeff, I have 115 on the seat and 320 over the nose and the lifters do bleed off but it seems to
take several days for it to make noise at start up. I've seen the kill switch trick and it works pretty good. I have an old HyFire 6 that
will retard 0-10* below 500 rpm and it seems to have no effect. Maybe the starter is spinning it above 500 rpm? Camshaft was
chosen for max midrange torque and long service life on the street, it's designed for 1.6 rockers so .500 lift at valve.

Fbird you may be right about locking the dist but I would sure hate to and this cam is not really that big. The dist has 10* mech
advance all in @ 3500 to allow for cheap gas with the old shortblock. This is in a Chevy LUV so not a big truck like you guys are thinking,
just a street toy. Ran 11.90 with 360 and same cam only at 236 @ .050 dur on street tires.This new 388 is not that strong. I guess I need
to score a piston stop and a degree wheel. I do blame the tunnel ram on Fbird.

GMRocket the HyFire 6 and summit billet dist have been on the truck for years and have worked flawlessly,but anything is possible.
I have rerouted all the plug wires to avoid inductive crossfire although they have also worked for years with prior routing.
Rebelrouser, I had not thought of that,.I can probably hobble out there and get the plugs out and a valve cover off. Thanks all for
the ideas and advice.

[Baprace]

madmooney , I don't know how you are going to degree that cam without a piston stop and a good degree wheel. Second item bobmc asked about cranking compression and you gave him valve spring pressure numbers, Last item, Usualy the numbers on the crank gear are expressed in cam degrees and not crank degrees, meaning if you take the cover off and find the gears on dot to dot using the 0 dot mark on the bottom gear do not assume that you can just move the bottom gear to the 4* + mark and all will be well, on most gear sets moving to the + 4* mark will result in +8* at the crank using a degree wheel, I find the crank gears numbering off on most sets, some of the real high end sets are correct. You have to read the degree wheel to set the cam timing , do not rely on the gear numbers. Last , is this the first time for a tunnel ram intake ? Not sure that I explained the issue correctly for an amature engine builder, I am not knocking you in any way, but some of these cams are just off, I had a SBC cam I ordered for a stock car engine and it degreed in OK on the Intake timing numbers BUT the cam had 10* too much duration on the exhaust and was not usable for the application, the slip had the numbers I wanted, the cam also had the correct code numbers stamped into it, but the cam was incorrect, and this cam was ground by the biggest cam grinder east of the mississippi <sp ?

[madmooney]

Baprace, ya it looks like I'm in the market for a stop and degree wheel, maybe I can borrow one from the mach shop. I have 30+
years in roadbuilding eqp design, manufacturing and service so i understand the basics but am far from an expert. So yes I was
shooting for 8* total 4* at the crank gear and 4* ground in the cam.I suspect you are right about the gear being off and hope you
are wrong about the cam being bad , but something is for sure not right. Have had the t-ram for a couple years now, it's the small
Weiand street ram with 600 eddys. Midrange throttle response is unreal but it's not a high horsepower/rpm deal. I love it.