1983 Cadillac Seville HT410 Pops/Backfires from Throttle Body

[bcroe]

If the Riv is providing the parts, I would take out the half shafts, then
pull the whole engine/trans/final drive package to keep at your project. 
Many junk yards do not want to take the engine off anyway, I got a lot
of free transmissions that way.  Bruce Roe

[Vinny6t6]

Holidays have past, finals have past, parts came in and my son and I tore down the HT4100.  After getting through the vacuum lines and Smog attachments, it tore down like a normal motor.  When we took off the timing cover, the plastic cam gear was worn and the chain was floppier than a puppy dog's ear.   Even worse, when we took the cam out the first lobe was worn down to an almost perfect circle.  Lifters we good except for the lifter that went on the first lobe.  It was almost worn to a U shape. (no Lie.  I kept it because I was in shock).  Now for the best part........Teaching my son how to put everything back.  With my help he has installed a new cam, lifters, pushrods, and full timing set.  He is cleaning every part before he puts it back on.  Intake, timing cover, etc.  What an experience working side by side, teaching him about lining up timing marks, researching the FSM to find torque figures and tightening sequences.  We ordered some more parts that we have to wait to come in before we can continue (Rad hoses, cap, rotor, plugs wires, ETC).  I know it'll still be an HT4100 when done, but the pleasure of passing on this hobby to him and teaching him what to do is priceless.  I'll post when we are finished and the results.

[Eric DeVirgilis CLC# 8621]

Even worse, when we took the cam out the first lobe was worn down to an almost perfect circle.  Lifters we good except for the lifter that went on the first lobe.  It was almost worn to a U shape.

There's the trouble of the backfiring which is what I suspected originally.

I'm surprised the teardown was managed without chunks of aluminum coming apart with bolts as they were turned as had been the case with one I encountered.

Interested to hear how the engine performs & sounds once reassembled and back on the road. There is very little feedback experience from those directly involved in HT4100 rebuilds.

[Vinny6t6]

I will.  I'm trying to post some pics too. Putting the block back together was actually straight forward.  Now its dealing with the miles of smog hoses and replacing split  or cracked hoses along with fixing years of butchered wiring.  Thank god for service manuals

[TJ Hopland]

Its good that you found a/the problem.  Nothing worse than going in that deep and not really seeing anything.  I suspect my 4.5 had a similar issue brewing.  It still smooths out when you start making power so mine must still have a little bit of a bump on it.   Really makes you wonder if that was a bad lifter or maybe that end of the cam was kinda hanging out of the furnace during treating.   Its it actually the first lobe or is it the 2nd one? 

Head bolts are the only ones that really seem to get good and stuck on these but the older they get I'm sure they don't get any easier.   Last one I took that far apart was over 10 years ago now.

Its kinda a shock when you pull the intake on those and see that half the head is part of the intake.  But after you think about it with aluminum intake and iron heads why have iron in places it really doesn't need to be. 

I'm sure the 4100 is like other engines where they are going to try and trick you into putting the dizzy in 180* out.   Timing marks align on the exhaust stroke for #1 so you either need to rotate the crank one full turn or install the dizzy with the rotor pointing to the terminal for the 5th plug in the firing order.   I'm too lazy to go find a manual but I think #6 is the 5th on those engines as long as Who is on first.

[76eldo]

It’s worth whatever you are spending to have that experience with your son. Sounds awesome. Please keep us updated on your progress.

[James Landi]

Soft cams, replacement gasket/bolts (the "special" bolt kit is made to remediate gasket failure at for intake manifold), also, check for worn front main bearing, as these engines developed crankshaft knock (aka deathrattle) as the front main bearing wore and the crank would move horizontally (easy to check by pushing fore and aft on the crank shaft pulley. You likely have to check the flow on the exhaust, as cat/converter gets clogged and lots of exhaust back pressures are bad. Have your radiator serviced--(aka de scaled--- )   Also, I had an 84 4100, that finally died at 317,000 miles--- never raced the engine--- never pushed the throttle --- was babied throughout its life, and I NEVER, NEVER used any cooling system pills that are other than G.M. I also set up an electric cooling system under dash heat gauge, as the idiot light is impossible to read if it goes off on a hot, sunny day. Good luck with your project,   James

[Dave Shepherd]

I would suggest looking at the rod bearings, my experience with these engines taught me that all that metal  from the lobe was not trapped in the filter , some wound up ground  into the bearings.

[Vinny6t6]

Last night my son cleaned the timing cover and replaced the water pump gasket and thermostat gasket even though it was not leaking.  I told him since the gaskets came in the set, do it for preventative medicine.  He even replaced the front crank seal.  When we took out the distributor, I noticed the gear was worn so I replaced it.  He was a little nervous about dropping it in and getting it aligned so I showed him what to do.  With the timing marks aligned on the timing set and the rotor pointing to the #1 cylinder mark that I made, it slid right in perfectly.  I put assembly lube on the gears before I slipped it in and put on the distributor hold down clamp while I had the room and just snugged it. By Friday the valve cover gaskets, radiator hoses, water temp sender (I broke that taking it off), cap, rotor, plugs and wires come in so some time this week, I'll help him put on timing cover and harmonic balancer.  Then the rest is gravy, except for the smog equipment (Grrrrr).  What made me laugh is that the valve covers that came off where chrome and he spent two days, cleaning and shining them until they looked like a mirror.  I tried to explain to him that this is not a 69 GTO, but he's learning. 

[TJ Hopland]

I forgot about the fact that these engines were known to eat distributor gears.  One of those strange things that most other engines found easy to get right.  Something about the oil pump or oil flow design putting extra load on it?? 

While its still apart I would confirm you have the distributor in correctly.   Its easy with the valve cover off, just look at the the rockers/valves.   

If the marks are aligned for installation which is usually crank 12:00 and cam 6:00 I would expect that you will see one of the valves on #1 open (the exhaust valve).   Valves on #6 should both be closed and the rotor should be pointing to the 6 terminal. 

If the marks are at 12 and 12 then both valves on #1 should be closed and rotor pointing at #1 terminal.   Not that you would care at this point but the exhaust valve on #6 will be open.

This is usually how it is and for some reason the manuals don't make that clear that you don't want to install for #1 with the 12 and 6 config.  Its possible that there are engines that are not that way but no reason to take a chance especially since its still apart.   Timing cover off, valve covers off, and no distributor cap its literally just a matter of looking at it.

If you wanted to just for education purposes you could turn the crank 2 turns and follow through the firing order looking to see that both valves are closed when the rotor is pointing at that terminal.       

[Vinny6t6]

I have to check this out!!  I don't remember the position of the valves.  All I know is that the cam dot is at 6 o'clock and the crank is at 12 o'clock and I positioned the rotor to point to the #1 terminal.  I've done all my engines that way.  I have to recheck this