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I have a 1985 Bronco which originally came with a 351W, but at some point a 302 of unknown origin was put in. I don't have much history.
Bronco sat for an extended period of time, but has great oil pressure etc.
There is a bad vibration at about 1700 RPM (definitely a harmonic imbalance vibration) and there is generally a lot of vibration even at idle (probably a combination of vacuum leak/harmonic imbalance).
My suspicion is that the flexplate off the 351W was used (28oz) along with a store-bought 50oz harmonic balancer for the 302....
Is it possible to identify the flexplate weight based on the picture below ? All i can see is C5AE and what appears to be a drill hole on the weight.
Depending on what weight it is I will install the appropriate harmonic balancer
You can't install a 28oz flexplate and then install a balancer made for a 28oz inbalance 302, and expect it to work on a 302 that came from the factory with a 50oz balance.
1st thing to do is determine the year of the 302. It should be over the starter, you might have to take the starter off to see it. Look for any clues anywhere else. The C5AE is a date code. It's a 1965 date code. If that came with the engine, that means it might even be a 289. They did not make a 351w in 1965.
If it indeed is a early 289, then it will be a 28oz inbalance.
Thank you very much. Also,is there a reason why an externally balanced engine cannot use weight matched flexplate and harmonic balancer and be just fine ? In other words if a 302 that was designed for a 50oz used a 28oz flexplate/harmonic balancer it appears that is not OK based on @Franklin2 's response... Ford must have gone to 50oz on the 302s (~81 and on) for a reason, I can't seem to recall or find why they did that....
You are right on the balance.
It all has to do with the crank, rods & pistons.
If they were made for a 28 oz weight then using a 50 would throw off the balance and it will shake its self to death.
Same for a 50 oz motor using a 28 oz weight,
It all has to match
Dave ----
I was able to get the numbers behind the starter. It is E0AE D3C. Looks like a 1980s 302. My other 1984 bronco with original motor has the exact same casting number.
I was able to get the numbers behind the starter. It is E0AE D3C. Looks like a 1980s 302. My other 1984 bronco with original motor has the exact same casting number.
How can I be certain which harmonic balancer should go on this with the 80s 302 ?
Now you are in a real pickle. They changed the balance of the 302 in and around 1981.
See if you can be a detective. You said they most likely used the 351w flexplate. That sounds plausible, the path of least resistance to them. You also said you think the balancer is not original to the engine you have now? Do you know where the balancer came from? If you were confident that the balancer came with this engine, then you know the flexplate is wrong since you have a vibration. You have a real puzzle here. Thanks Ford!
The "bad" balancer that is on currently, its source is unknown. The previous owner stopped using the Bronco after the harmonic balancer was going "bad" and needed replacement. He said warranty provided this replacement motor. He mentioned being happy with it until then, especially with gas mileage. Per him this 302 had less than 50K miles before it was decommissioned. Not sure if that 50K total or 50K on top of whatever else was on the 302 when it was put in.
They also used the alternator bracket from the 351W, the heater hose is squished. Not a high quality swap by any means.
Does the balancer need to be pulled for identification ? I can see it has 4 bolts. I'm hoping I can replace it with the same kind and hope for the best.
If thats no-bueno that means the flexplate will need to match whatever 302 Crank is inside... a lot of labor. Probably worthwhile to find a 351W long block somewhere to bring the Bronco back to original setup. Don't want to go the extra mile to make an unknown 302 work.
Did he drive it with the vibration, or did it start vibrating when the balancer went bad? The balancers will separate sometimes, especially if they get a lot of oil of them and it degrades the rubber. They can actually slip and throw the timing marks off. Maybe the only problem is the balancer causing the vibration?
I took the balancer out, very evidently a 50oz balancer, but the flexplate is a C5AE which we believe is 28oz. Therefore the vibration must have existed all along... I do not know how much it was driven with the vibration (at least don't remember).... It's been a LONG time since I spoke to previous owner. Even his recollection was of a 15 year old memory.
If a lot of driving with this apparent mismatch, then the bearings are suspect and shot... or hanging in there waiting to be rescued. Anything besides bearings to worry about? Oil pressure is very good (at least based on gauge). I also know oil pressure is good because there is a lot of leaking from the old valve cover gaskets
Lastly, do I swap back with a pre-80 28oz 302 balancer or a 28oz 351W balancer? Which has a better shot of reasonable survivability? The flex plate belongs likely to the 351W and is likely 28oz.
I don't think the balancer's interchange from a 302 to a 351w? I haven't been into in years. I was doing a little research earlier, if you are going to pull the engine and tear it down some, I think I read that the 50oz crankshaft will have 2MAE on it I read that the 28oz crank will have 2M or 2MA on it.
Thanks much for the suggestion of identifying crank! Just recently did a 2 piece seal on a 460 and I am not revisiting an oil pan removal again for a while. The 302 oil pan should come out easier but still needs the motor hoisted, blocked off, oil pick up tube coming off, etc. The effort to pull the oil pan is quite excessive on these bullnose trucks.so probably hold off for now.... I would rather wait until a good 351W core comes along.
I also saw that another possible correlation of 50oz vs 28oz is 1 piece vs 2 piece rear main seal. Is there any externally visible indicator of 1 piece vs 2 piece rear main ?
OK i was able to confirm the casting date, had to remove the starter
The casting date for the 302 of unknown origin is 2C30, which corresponds to 1982, March 30th
I also checked my 1984 Bronco for consistency, it shows to be 3H31 which corresponds to 1983, August 31st
It would seem the 302 is 1982 which means it likely has a 50oz imbalance crank, which explains why a 50oz harmonic balancer was installed. The flexplate however is from the 351W at 28oz, no wonder the vibration is present. What is the best course of action ?
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