3ac to 4ac swap; have motor and questions...

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overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

I cut out a chunk and that gave me the room I needed to get more rotation on the distributor. Test drive time!
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Good times!
Bruce
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overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

That worked!!! Now on to tuning the Weber!!

Good times!
Bruce
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ARCHINSTL
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Re: 3ac to 4ac swap; have motor and questions...

Post by ARCHINSTL »

Where does your PCV hose attach?
Is that another horn attached to the front top X-member?
Tom M.
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overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

Hi Tom! Yes, another horn. I discovered the original still existing but not functioning behind the headlight, but haven't swapped them out yet Previous owner evidently added one after the other quit. I put my PCV on the intake manifold-here's pictures. I left the PCV hose long and don't run it hanging down like that but it tucks nicely on the back side of the air filter, out of the way.
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Then attached the breather line in the air cleaner. I put the weber on the old 3ac 4 years ago so I have forgotten about the mess I replaced when I converted from original carb and all that goes with it!!

Good times!
Bruce
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Petros
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Re: 3ac to 4ac swap; have motor and questions...

Post by Petros »

you should not have to alter the distributor to get the timing correct. If you run out of travel that usually means the distributor gear is off a tooth or two, or the timing belt is off a tooth. it will not run properly if either is the case, you need to check your timing belt (cam sprocket should line up with marks when the engine is at TDC based on crank shaft front pulley mark per the FSM), and than follow the procedure in the repair guides to get the distributor installed correctly.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

Hi Petros, yea I did all that and went back and forth with the distributor between teeth. The belt is perfect! I suppose the cam/dist gears could be worn down?

Good times!
Bruce
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

I used the 3ac distributor from my original engine. I have checked the belt three times. However the belt timing seems logical for what the "symptom" is! But after checking the belt timing, and then taking the cover off and checking again the next day - before cutting the hold-down on the dist, I could not get the timing dialed in as I described earlier. Anyhow I am able to get the ignition timing retarded to a point where no detonation with the extra few degrees that the extra rotation gave me. I went back and forth with the distributor between teeth a half dozen times minimum. I've got 50 miles on it now. But I think I will pull the cover off and check the belt timing ONE MORE TIME!! It only takes 30 minutes!

Good times!!
Bruce
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Re: 3ac to 4ac swap; have motor and questions...

Post by jimcrazy »

run in to the same problem in my fwd wagon, blamed it on gas getting shiter , had to keep retarding the timing to get rid of the spark knock till I ran out of travel, ended up being the mechanical advance in the dizzy was seized up,, freed that up dizzy back in about the middle of the adjustment slot
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Petros
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Re: 3ac to 4ac swap; have motor and questions...

Post by Petros »

good point Jimcrazy, come to think of it that was a problem in a few others.

check for free play of the distrubtor weights, and us the timing belt to see if the spark advances when you rev the engine with the timing light pointing at the timing mark. If it does not advance the spark with rpms, than the mechancial advace is stuck. you need to fix that because it will get poor fuel economy and eventually could cause damage to the exhaust valves or head gasket.

usually if you soak it in penetrating oil you can work it free so it it will freely advance. Other times you have to take it all apart and clean the parts so they advance freely.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

OK GREAT!! I just rechecked the timing belt for the 4th time-perfect like the last 3 times! And the seized advance seems like that is it now to think about the driving characteristics that actually were present with the previous 3a-so I'm going to go pull it now! Thanks Jimcrazy and Petros!

Side note- I have had so much fun and re-connected with the little wagon that I ebayed some Sterling oversized pistons and rings and some valve guides for a overhaul down the road...this motor seems to be OK but the rod bearings compared to my 3a with 35,000 miles since rebuild (re-ring only) which looked BRAND NEW make me want to start gathering.

Good times!
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

I don't have a timing light. I have the distributor out and the vac advance pulls the mag pickup plate smooth and far! I hear the mech weights flopping back and forth under the plate and can see the springs and weights and they look dry and crusty but weights are flopping around!

EDIT- The mechanical advance is seized! Lubed it up good and see what happens! The distributor was seized 3/4 advanced! No wonder! I have worked it over for the last hour and a half working it back and forth with silicon spray and it has loosened up to be able to pull itself back to the stop! So back together it goes!
THANKS GUYS ONCE AGAIN!!

Good times!
Bruce
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

This has been asked before, but I need to hear it again...is the 3ac head the same as the 4ac cyl head-meaning the 3ac head will work on the 4ac block? My 4ac is plugging along but has one really bad cylinder. I have the 3ac sitting here The crank on the 3ac looks perfect and the bearings, although w/30k, looks super excellent! The 4ac bearings I pulled for inspection looked well worn and the crank will need at least polished! I'm considereing using the 3ac crank in the 4ac build which is right around the corner-Christmas present for the wifee! If I can use the 3ac head, I can freshen that up as well with less down-time before pulling the other motor. I believe all this will work, right? I have new oversized pistons and rings, and a good machinist too!! The other option of course is to put new valve seals in the 3ac and drive on with a slow build on the 4ac. Thanks for the info!

Good times!
Bruce
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Re: 3ac to 4ac swap; have motor and questions...

Post by teranfirbt »

They're close enough that it's a direct swap. 3AC and 4AC parts are pretty interchangeable other than pistons, at least as far as the larger assemblies go. Hell, I'm using my old 3AC block, crank, and rods for my 4AFE.
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Petros
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Re: 3ac to 4ac swap; have motor and questions...

Post by Petros »

the crank is identical, but the 3ac/4ac head is different though it will interchange. The combustion chamber must be smaller on the 3ac because both the 4ac and 3ac have the same compression ratio and same stroke, which means with a larger piston dia (bore), you would need a larger combustion chamber in the 4ac to get the same CR.

Also, the water jacked is different, the 4ac cools better around the exhaust valves, which was one of the problems I found with the 3ac with high compression, it causes premature head gasket failure. Putting a 3ac head on a 4ac will run, but you will have very high CR which means you must run premium fuel, and likely get head gasket failure in 3 to 6 months because of the uneven cooling around the exhaust valves.

Also, it is a lot easier to replace the valve stem seals on the engine in the car that swapping out a whole head. Keep the matching head on the engine and replace the stem seals, and take your time to do the head properly.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
overs10ded
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Re: 3ac to 4ac swap; have motor and questions...

Post by overs10ded »

Thanks Petros! I pulled the head on the 3a today as I'm going to use that crank, and possibly rods since I could get the new pistons set up for the 4a before pulling it for the rebuild. I can scavenge the 3a heads for cam, spings, valves, ect for the 4a if needed, correct? I have new exhaust valves and guides as well for the 4a rebuild. Thanks for the information!!

Good times!
Bruce
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