Starting my 2.4 after top end rebuild

[neilca]

I have finished my rebuild of my 2.4 race engine and tried to fire it yesterday. Something is out of time. The engine backfires when cranking. Now for some background.

My engine is run via a Megasquirt 3 with a crank trigger, oil temp sensor, air temp sensor and a throttle position sensor. I have two distributors, one in the stock location the other is at the end of the cylinders 123 camshaft. The crank sensor tells the MS3 when to fire the two MSD's that then go to the distributors to fire the twin plugs. All of this worked properly prior to the top end build.

I had blown all but one head gasket while running 12.5:1 pistons with too much timing. I have reduced the compression to 10:1 during the rebuild. So when I timed the cams I started with the 123 cam. This set which TDC would be the firing stroke. The distributor to cam relationship is one way, it cannot be assembled 180 degrees out. Following Wayne's book, I then set the cam timing on the 456 cam.

So now something is out of time. I disconnected the stock location ignition since it can be timed 180 and tried to fire the engine. Same thing plus a big orange fire ball from somewhere.

What I think is that the 456 cam is timed 180 degrees off. I think the MS3 triggers every time the piston comes to TDC so the 456 side is firing on the exhaust stroke. Is this possible? Can I pull the chain covers and check elative positions of the keyways to verify if they are 180 out?



Merry Christmas all,

neilca

[Lapkritis]

A 12v OHC dual bank 6cyl will run with a single cam out 180° under some protest. If you have bad backfires then I would double check the firing order/plug wires in case a couple were mixed up.

If the plugs wires are in order then I would move to confirming the cams are in time... I would pull an upper or lower valve cover to on the bank for 4-5-6 and confirm the lobes are correctly phased at #1 tdc. No need to pull the engine nor timing covers.

If those check out then double check your engine and ecu grounds...

Merry Christmas.

[neilca]

I have checked the firing order of the wires. They were correct. Guess we need to check cam timing.

[swade]

Merry Christmas,

The way you have your intakes numbered in the top photo (#1,#2,#3) is reverse of normal. Number one cylinder is nearest the distributor. Maybe just a wire swap away.

Wade

[neilca]

The stacks were just thrown on there for the picture, they are out of order. I will go back and verify the wiring. One thing I have learned about trouble shooting one of these engines, verify everything you know.

[swade]

I had a long troubleshooting period when I set up my 2.4 with twin plugs, a very frustrating time. I had my engine out twice to figure it out. I had what I thought were timing issues but in the end my (new) lower valve covers were just enough closer to the valve adjusting screws that they were keeping them open a hair.

Keep at it, you'll find it

W

[neilca]

Well I figured it out. I did time the cams incorrectly. The 456 cam was firing as the intake valve was opening. This is because I set both cams to the same TDC. I know that may sound weird but in a 4 stroke cycle the piston is at TDC twice in the cycle. One cam gets set to one of these TDC's, the other is set to the other TDC. I have decided not to remove the engine again and set the timing in the chassis. It is an incredible PITA since the chassis is a 914. I hope to have it done today.

[304065]

Yes, one is up when the other is down, not made any clearer by the threads out there.

Here's a chart I made that helped me think through it. Glad you fixed the issue.

Cam timing chart

[swade]

Did you get it running?

[neilca]

Yes and no. The engine did start and ran. I put a timing light on it to verify the computer was reading the actual timing. I couldn't see the timing mark. I had the light hooked to the #1 top plug so I checked the indexing of the distributor and found it to be one plug off. So I fixed that and it wouldn't run. So I changed the settings in the MS3 for timing offset back to where it ran before and it wouldn't run. I increased this amount and it fired up. But now it misfires when I try to rev it. I am going to look at the trigger wheel today. I know perseverance will pay in the long run.

[swade]

Just a thought, could you disconnect one of the ignition systems and focus on just getting it running as a 6 plug, then later bring in the other 6 plugs? Maybe they are firing at different times? Really just thinking out loud. I don't understand why you have a trigger wheel and 2 distributors though, it sure is a nice looking installation.

[neilca]

Swade,

I am running a Megasquirt 3 ECU so the trigger wheel feeds the data to the computer. The computer triggers the two MSDs for the twin plug heads. Why? it was the cheapest way for me to get twin plug ignition and electronic fuel injection.

The engine is working fine now. I warmed it to 200 degrees F. Ran fine even at high RPMs. Next step is the dyno.

Thanks,

neil

[Lapkritis]

Good to hear. What was the fix???

[neilca]

The best I can tell was the proper indexing of the two distributors. The problem with infinite adjustability is the right answer is finite.

Happy New Year!

neil