Author Topic: 340 Engine Build... it all started with a rear main seal leak! (Read 1889 times)

Tonker1 · « **on:** November 19, 2018 - 11:40:22 PM »

Opened up my '72 low compression 340 because of a rear main seal leak and now I'm doing a full engine rebuild!! There were lips in the cylinder bores, one of the piston rings was snapped, and there were cracks in the valve seats that are getting ready to enter the water jacket!

I'm looking for some help working out what pistons to buy with the cylinder heads and if the cam and carb are too small. I drive the challenger to work everyday so I get most of my fun in the lower rpm range and I'm looking to build some low end torque, but I can't afford a daily driver that constantly needs filling up on 100 octane fuel either!

The first thing is to bring the compression ratio up from 8.5:1. My summers are about 95F. I considered a full new rotating assembly and stroking it as that would build a heap of low end torque, but that will break the bank too much!

My other thought was that ported iron heads would be better for the low end than new aluminium heads, but I can get a set of assembled edelbrock 63cc 60779 or 65cc 60179 with the extra .060" clearance. I have a friend who will sell me a set of either unused at a really good price. For pistons I was thinking hypereutectic aluminium by KB as I won't be making that much power and don't have plans to go bigger.

If I was looking for about 9.5-9.7:1 would that work on 87 octane pump gas with the aluminium heads and that cam?

To get a quench of 0.040" would I be better off using a flat top piston that sits proud of the block with the 60179 head or a shorter piston with the 60779?

Engine currently
-Bored: 0.030 over for 4.070"
-Carb: Holley 670 street avenger w vacuum secondaries
-Cam: Lunati 10200702. 220 int./226 exh @ 0.050" lift, total lift on stock 1.5 rockers 0.475 int./0.494 exh, lobe seperation 112
-Intake: Eddy 7576 performer rpm dual plane air gap
-Ignition: MSD 6AL, MSD Billet Dist, MSD Blaster 2 Coil

To reuse
-Cast crankshaft
-Forged connecting rods, #3418645 318/360 rods, fitted for 0.9842 floating pins. No offset. (jimynick)
-Stamped nonadjustable 1.5 rocker arms (jimynick)

Other components already on car
Tko600 trans, 4.10 diff gears, 2.5 inch exhaust and some no name aftermarket headers.

Cheers in advance. I've been working through a pile of books on hot rodding and rebuilding small block mopars, but I need some help understanding which way to go with it all!

Beekeeper · « **Reply #1 on:** November 20, 2018 - 11:09:33 AM »

If you like your current camshaft, I�d reuse it but if you do, it is imperative that each lifter go back to the same lobe. Not sure if you bothered marking them during breakdown. Mixing them is guaranteed failure.

Anyway, given what you are trying to do, I�d focus on getting your compression up to 9.5 to 1. Won�t need special fuel and it will allow most cams to really perform. They have compression calculators online to help but I�d sit down with your machine shop on this. Let him order your new pistons. Cast pistons are way better today than in earlier years and will easily handle the kind of power you are looking for. Spend the money saved on heads. Also, make sure your shop resizes the rods using new rod arp rod bolts. A good insurance policy. Don�t be afraid to have the new heads milled to achieve the correct CR. If you wind up under 9:1, I�d go with a cam designed specifically for low compression motors to give you decent low end.

If the machine shop is good, they should be checking the actual ccs of your new heads (they are rarely what is advertised), adding in the right gasket thickness (they sell thinner ones to help increase CR), and carefully selecting pistons that will not sit too low in the bores killing CR. That cam will really wake up with the extra compression.

On overheating, I know a lot of guys disconnect the vacuum advance. Trust me...don�t. Set it up so that it kicks in under cruising and idling conditions (when the engine is pulling max vacuum). The engine will love you for it and run so much cooler. I used to always disconnect and then constantly struggle with high temps even on cool days. Once I rediscovered how important it is, I�ve run these cars through 110 degree deserts with no issues.

Beekeeper · « **Reply #2 on:** November 20, 2018 - 11:14:48 AM »

Oh, and I think that intake and carb should work nicely. If you have overdrive trans, definitely 3:73 gears or 4:10. Good choice on the msd ignition stuff.

I�d go with HP iron manifolds. Headers suck. Even when they don�t leak, they add tons of heat into an engine compartment, are way louder inside the car, never seem to fit very well causing ground clearance issues, and they make it harder to work on the car later. Since you want a low end stump puller, headers aren�t really all that necessary.

70chall440 · « **Reply #3 on:** November 20, 2018 - 12:30:40 PM »

Some good advice there. If you are not in a hurry, spent some time port matching the intake to the heads and the manifolds to the heads. Don't need a lot but it will help the engine run as good as it can. On the exhaust side, you need to have a good system all the way back, probably do not need to go larger than 2 1/4.

Tonker1 · « **Reply #4 on:** November 20, 2018 - 08:04:57 PM »

Thanks for the replies!

I'm looking at three options for heads and pistons!

Option 1:
Head: Eddy 60179 65cc
Piston: KB 243-030 hypereutectic aluminium
Head volume: +6cc
Above deck: 0.020
Gasket bore: 4.180
Gasket thickness: 0.060 (quench 0.040)
Static compression: 9.844
Dynamic compression: 8.468-9.12

Or option 1A with different gasket thickness
Gasket thickness: 0.070 (quench 0.050)
Static compression: 9.61
Dynamic compression: 8.26-8.91

Option 2:
Head: Eddy 60779 63cc
Piston: KB IC9975-030 forged aluminium
Head volume: +7cc
Below deck: 0.008
Gasket bore: 4.180
Gasket thickness: 0.04 (quench 0.050)
Static compression: 9.747
Dynamic compression: 8.177-9.03

Or option 2A:
Gasket thickness: 0.050 (quench 0.060)
Static compression: 9.510
Dynamic compression: 7.983-8.44

To work out dynamic compression ratio I've a whole range of calculators (KB pistons, Wallace Racing, Port City engines and like 3 others) I understand it is only a theoretical value and is influenced by a whole range of factors. But those differences in numbers are values are huge! Is dynamic compression ratio something I should really concern myself with.

I think the second options are generally better as it uses a forged piston and the piston does not stick proud of deck height.

I assume with that cam, stock rockers and the springs that come on assembled eddy heads valve float will occur somewhere around 6500-6700rpm? Which would be above peak power and the shift point of that cam anyway?

My 5th gear is a really nice 0.64:1 so the 4:10s are still nice on the highway!

70Chall40, I'm currently reading David Vizards how to port and flow test cylinder heads!

70chall440 · « **Reply #5 on:** November 20, 2018 - 09:01:12 PM »

Tonker - excellent, I think that it is beneficial.

jimynick · « **Reply #6 on:** November 20, 2018 - 10:29:32 PM »

Reading this thread a couple of things came to mind. The pistons which come out of the bore .020" and you say the gasket is .060- is that the compressed thickness? Not likely and the common thickness for a compressed gasket runs in the .030 range, which, if so in this case, would leave you with approx. .010 piston to head clearance- and that isn't enough, especially when I read about 6500 rpm engine speeds. You also mentioned cast rocker arms. Stock 340's use a stamped steel arm, but the early LA's could be found with cast rockers that're adjustable; which do you have? HyperE pistons run with very close tolerances and don't like to be shocked much either, so machining is, as it should be, even more critical and the final hone can make or break the ring sealing. Your connecting rods will not be cast either. "
FWIW,...Info from page 45 of "How to rebuild your s/b mopar" says (forging#) 2899496, (floating pin, .100" offset), were used on all 340s as well as 72-73 318" but Bee's advice on the rods is good and you should take it. Something else to consider is the oem Chrysler "308" casting # head that Chryco Psycho claims are good for 30 HP over the X heads. With a daily driver, I'd also weld bungs into the header collectors for a wide band O2 sensor to get the mixture optimized to cut down wear on that soon to be new engine. Just my

Tonker1 · « **Reply #7 on:** November 20, 2018 - 11:09:59 PM »

Quote from: jimynick on November 20, 2018 - 10:29:32 PM

Reading this thread a couple of things came to mind. The pistons which come out of the bore .020" and you say the gasket is .060- is that the compressed thickness? Not likely and the common thickness for a compressed gasket runs in the .030 range, which, if so in this case, would leave you with approx. .010 piston to head clearance- and that isn't enough, especially when I read about 6500 rpm engine speeds. You also mentioned cast rocker arms. Stock 340's use a stamped steel arm, but the early LA's could be found with cast rockers that're adjustable; which do you have? HyperE pistons run with very close tolerances and don't like to be shocked much either, so machining is, as it should be, even more critical and the final hone can make or break the ring sealing. Your connecting rods will not be cast either. "
FWIW,...Info from page 45 of "How to rebuild your s/b mopar" says (forging#) 2899496, (floating pin, .100" offset), were used on all 340s as well as 72-73 318" but Bee's advice on the rods is good and you should take it. Something else to consider is the oem Chrysler "308" casting # head that Chryco Psycho claims are good for 30 HP over the X heads. With a daily driver, I'd also weld bungs into the header collectors for a wide band O2 sensor to get the mixture optimized to cut down wear on that soon to be new engine. Just my

Any all advice and info before I open up my wallet is really appreciated!

Those were the compressed head gasket numbers. For gaskets with compressed height above 0.060 I was looking at using cometic.

The rockers are stamped nonadjustable.

I have an innovate motorsports wind band 02 sensor and vacuum gauge that i use to tune the carby with, I need to retune winter and summer as temps vary from 19-95F

So just checking the forging number on my rods, they are 3416845 which is the 318/360 rod. Which should have a 0.9480 wrist pin. However measuring the OD of the pin and ID on the rod show with my bore dia gauge shows pin diameter of 0.984 which is the size of the 340 rods!!! If the numbers on the reverse to the forging are the batch set, the conrods were not made together. The wrist pin definitely floats on the con rod. This means I would not have the 0.100" offset of the 340 pushrods, does this mean the piston would being trying to tilt in the bore? Looking at new con rods on summit racing they do not list an offset and the applications include both 340 and 360 motors. I'd greatly appreciate if someone could explain this to me!

Option 3: I'm not sure on the valve clearances, what do people think
Head: Eddy 60779 63cc
Piston: KB 243-030 hypereutectic aluminium
Head volume: +6cc
Above deck: 0.020
Gasket bore: 4.180
Compressed gasket thickness: 0.054 (quench 0.034) I have an unused set of these already
Static compression: 10.18
Dynamic compression: 8.753-9.43

jimynick · « **Reply #8 on:** November 21, 2018 - 10:54:29 PM »

The 340's used a floating wrist pin that was moveable in the rod bore and held in place by circlips in the piston wrist pin bore, so it sounds right for your 340. Nobody advertises piston pin offset as it's non-variable and meant to load the piston to one side of the bore versus having it "flopping" about were it dead nuts in the centre. I don't claim to be any engine "guru" but, from what I have read, your last combo sounds doable to me, especially as it incorporates aluminum heads which'll allow you to run that 10-:1 CR that'll give you some decent power. Talk to your machinist as well and do your homework and you'll be ok. Vizard IS a wizard for my

Tonker1 · « **Reply #9 on:** November 21, 2018 - 11:36:28 PM »

That makes more sense, the offset is in the piston itself as opposed to the connecting rod.

The more I look at Option 3 the better it looks to me.

I'm still reading through Vizards book and absorbing as much knowledge as I can!

My only concerns for this were
1. the quench distance of 0.034", is this too tight? With material expansion and piston rock could the piston hit the head?
2. would there be sufficient valve clearance from the KB243 piston with the eddy head, is there anyway to work this out before buying the parts.
I've been reading through this thread and it seems like a viable option! http://www.cuda-challenger.com/cc/index.php?topic=55521.30

Option 3: I'm not sure on the valve clearances, what do people think
Head: Eddy 60779 63cc
Piston: KB 243-030 hypereutectic aluminium
Head volume: +6cc
Above deck: 0.020
Gasket bore: 4.180
Compressed gasket thickness: 0.054 (quench 0.034) I have an unused set of these already
Static compression: 10.18
Dynamic compression: 8.753-9.43

jimynick · « **Reply #10 on:** November 22, 2018 - 09:15:16 PM »

Based on what I've read, 35 thou seemed to be nearly optimum and they said that once you get over about 40 thou you start to lose the effect. I'd call Edelbrock, after gathering the specs on the cam and talk to their technical department. They'll likely be able to give you a max lift figure and knowing the rocker arm ratio, you can determine the clearance. You'll need to know if that +6cc dome is an issue and I'd also call KB'd tech department to see if they can shed any light on the subject. The final arbiter would be to fit a rod/piston assembly up and install it, putting the piston at TDC you could then used a dial indicator to see the depth that the valve goes before it contacts the piston and do the math from there. A bit of screwing around, but necessary to give you satisfaction and peace of mind.

Tonker1 · « **Reply #11 on:** November 25, 2018 - 09:41:08 PM »

Cheers for the advice!

I'll call Edlebrock on Monday, I've also messaged Trick Flow to see if there is any progress on their new heads as well!

I'm definitely going to perform those checks once I have the parts. The satisfaction and peace of mind are an absolute must!!

jimynick · « **Reply #12 on:** November 26, 2018 - 11:33:30 PM »

I'd say you're well on your way to doing the job right and making yourself happy. Good luck!

Author Topic: 340 Engine Build... it all started with a rear main seal leak! (Read 1889 times)

Tonker1

340 Engine Build... it all started with a rear main seal leak!

Beekeeper

Re: 340 Engine Build... it all started with a rear main seal leak!

Beekeeper

Re: 340 Engine Build... it all started with a rear main seal leak!

70chall440

Re: 340 Engine Build... it all started with a rear main seal leak!

Tonker1

Re: 340 Engine Build... it all started with a rear main seal leak!

70chall440

Re: 340 Engine Build... it all started with a rear main seal leak!

jimynick

Re: 340 Engine Build... it all started with a rear main seal leak!

Tonker1

Re: 340 Engine Build... it all started with a rear main seal leak!

jimynick

Re: 340 Engine Build... it all started with a rear main seal leak!

Tonker1

Re: 340 Engine Build... it all started with a rear main seal leak!

jimynick

Re: 340 Engine Build... it all started with a rear main seal leak!

Tonker1

Re: 340 Engine Build... it all started with a rear main seal leak!

jimynick

Re: 340 Engine Build... it all started with a rear main seal leak!