Rebuild or swap? 1970 Valiant

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skitzoid

skitzoid

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I have a 1970 Valiant 225 with a 904 3spd auto. I have had this car for several years and it was first car when I turned 15. While the 225 is bulletproof, no working odometer and no oil sensor can be a bad combination for a first time car owner. It got a knock, and so I swapped in a matching 225 and 904 but now the second engine is having some other major concerning issues, it stalls and backfires even after having it tuned by an expert( water jacket issues? Not sure).

I've looked at rebuilding my numbers matching 225(and my second if I feel inclined), but from videos I've seen there's a whole lot to go wrong. I'm mechanically inclined, but only for common repairs/ maintenance over the past 5 years that I've owned cars. It looks very daunting, and I'm debating just selling my 2 engines and trannies and putting in a professionally rebuilt 225 or 318.

Is rebuilding a 225 as difficult/complicated as it seems in in videos like this?


And since a rebuilt 318 is similar in price to a 225, how would the 1970 904 auto handle the extra power? If not what transmission would I need to swap in?

Any advice is welcome, thank you
 
The slant 6 and small blocks do not share the same transmissions. Their bellhousing bolt patterns are completely different, so that solves that issue. There's nothing "daunting" about building a slant 6, although the manifold assemblies are a little intimidating if you've never removed or installed them, but you're in the right place. Lots of us here can help you along the way if you get hung up.
 
You can't put a price on sentimental value. If it is strong then the money doesn't mean anything. I am a sentimental kind of guy. Since it's only original once, I would consider rebuilding the original motor.
 
keep in mind swapping from a /6 to V8 you'll need to consider all the peripherals: exhaust, motor mounts, transmission, fuel line, wiring, cooling just to name a few.

then you'll need to track down all kinds of fiddly bits like kick down linkage, throttle cable bracket and return spring mount, a new throttle cable, things of that nature.

even if you sourced a complete take out air cleaner to oil pan with a transmission attached you'd still be looking at several hundred dollars in associated costs.

if I were in your position I'd break down the one motor and have a machine shop do the head and rebuild the bottom end and supply it as just a short block. that way you can do most of the heavy lifting and learning along the way and not be too outside of your comfort zone.

that'll get your wheels back for not a ton of dough and you can decide if you want to dig deeper and do the other motor or save up and collect parts for a V8 swap.
 
Your K frame is also different. You'll need a small block v8 or simpler still conversion mount kit for the slant 6 frame. Take your motor apart and see how bad or good it is. If that's too much send it out.
 
skitzoid said:
...but now the second engine is having some other major concerning issues, it stalls and backfires even after having it tuned by an expert( water jacket issues? Not sure).
Click to expand...

Stalling and backfires aren't a water jacket issue. Those issues are probably a timing problem of some type.

Assuming the "expert" is competent but failed to check, might be worth checking your cam timing and make sure the timing chain didn't skip a tooth. If so (and it hasn't crashed the valves) it's just a timing chain and gears to fix it, not a full rebuild.

Just bring the number 1 cylinder up to top dead center on the compression stroke and see where the timing mark is. There are tricks to finding the compression stroke, like putting your finger in the spark plug hole and turning the motor until it puffs at you. Then bring the piston to the top using a wooden dowel or something to watch it.

Not saying there aren't other reasons you could be having the issue, just tossing it out there.
 
I would have a competent mechanic/person checkout the health of your engine, as in compression/leakdown, and IF good, get it running as it should. If bad, its your nickle as to what to rebuild, but like mentioned there is a lot of things to change if going v8 from that slant. Plus the cost of the SB.
 
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