1967 327/300HP engine balancer

[Timothy B.]

Is the 300 HP balancer in 1967 the 3896904 and when did the stepped version with the rivets like 1963-4-5 change to the later style.
'
My 67 has the later version that looks identical to the new 3896904 I have in the basement and I want to be sure it's correct. Also, is the single groove 3755820 lower pulley painted black or orange?

Thanks for the help

[Jeff S.]

Re: 1967 327/300HP engine balancer

Tim

3896903 is replacement for 66-67. I don't know the difference in a '904, and it does seem odd that the higher part number is listed for the earlier model years ... the 903 is for press fit (no drilled/tapped blind hole in crank). I'm not sure about the 904.

I was able to find an NOS '903 at a reasonable price after some on-line searching about 2 years ago.

My pulley ('66) is not painted Chevy orange. It's either semi-gloss black or perhaps that real dark green shade.

[Jack H.]

Re: 1967 327/300HP engine balancer

On paint/color issues like this (was it shot Chevy orange?), a good rule of thumb is to open up your copy of the AIM. If you see the part is called out for assembly in the AIM.

If so, that means it was NOT part of the engine sub-assy shipped from Flint/Tonawanda and therefore wasn't present when the engine was painted...

[Timothy B.]

Re: 1967 327/300HP engine balancer

I am confused, the 1972 parts book calls out a 3896904 damper for 57-65 and 3896903 for 1966-67 low HP cars. The crankshaft on my 67 is not drilled so my thinking is it should take the tighter 904 damper. Did the crankshaft OD change in 66 for this 3896903 damper or is there a error in the parts book?

I just measured a new 904 damper ID at 1.265" with a venier guage. What is ID for #903??

When is the approx. change over from the stepped riveted style damper like on my 63 to the new style damper like 3896904? I want to be sure everything is correct.

The reason I asked about the lower single groove pulley is because mine is painted orange with no traces of black or glassbeading underneith. It's also painted on the backside where it bolts to the damper so someone obviously has been there.

Thanks for all the responses

[Joe L.]

Re: 1967 327/300HP engine balancer

I am confused, the 1972 parts book calls out a 3896904 damper for 57-65 and 3896903 for 1966-67 low HP cars. The crankshaft on my 67 is not drilled so my thinking is it should take the tighter 904 damper. Did the crankshaft OD change in 66 for this 3896903 damper or is there a error in the parts book?

I just measured a new 904 damper ID at 1.265" with a venier guage. What is ID for #903??

When is the approx. change over from the stepped riveted style damper like on my 63 to the new style damper like 3896904? I want to be sure everything is correct.

The reason I asked about the lower single groove pulley is because mine is painted orange with no traces of black or glassbeading underneith. It's also painted on the backside where it bolts to the damper so someone obviously has been there.

Thanks for all the responses

Tim-----


The correct balancer for your application is the GM #3896903. This balancer was first used for the 1967 model year, although I suppose it's possible that very late 1966 also were equipped with it. Otherwise, the GM #3896903 is SERVICE for 1966 model year Corvettes with 300 hp.

The 3896904 is a SERVICE-only balancer applicable to all 57-65 Corvettes except 62-65 with SHP.

[Timothy B.]

Re: 1967 327/300HP engine balancer

Joe, I thought all undrilled cranks used a tighter fitting balancer and that would be 3896904 because that's the part to service 57-65 low HP cars. Does 3896903 have the same interference fit? What's the difference??

The crankshaft in my 67 does not have the retaining bolt.

[Timothy B.]

Re: 1967 327/300HP engine balancer

Jeff, Thanks for the picture of the 903 balancer, it looks like what's on my 67. The new 904 I have looks the same so I am courious what the difference may be.

[Jeff S.]

Re: 1967 327/300HP engine balancer

Tim

I don't know the differences in 903 or 904 & my 903 is installed at this time & not available for measurements. These are more difficult to find than 904 ... you might have better success at a Camaro parts vendor, as 903 was used on '67 327/210HP. Two more pics follow.

[Joe L.]

Re: 1967 327/300HP engine balancer

Joe, I thought all undrilled cranks used a tighter fitting balancer and that would be 3896904 because that's the part to service 57-65 low HP cars. Does 3896903 have the same interference fit? What's the difference??

The crankshaft in my 67 does not have the retaining bolt.

Tim-----


I used to think that, too. However, I've recently come to question that. For years I've been intending to re-measure the ID of the '903' and '904'. But, I never got around to it.

"Officially", I don' think 66-67 300 hp had the crankshafts drilled and tapped for retaining bolts. In actuality some may have received such cranks, though. However, I feel pretty confident that the interference fit for the balancer would have been based on the "official" configuration of the crankshafts and, as I say, that would be without balancer bolt.

The GM #3896903 was the balancer originally used for 1967 300 hp applications. Ergo, it would seem to me that the 3896903 must have been designed for use with a crankshaft without balancer bolt.

[Timothy B.]

Re: 1967 327/300HP engine balancer

Thanks Jeff and Joe for the good information. I measured the ID of the new 904 I purchased from GM back in the eighty's at 1.265. This was purchased for my 63 but it's not the original configuration. It's still in my basement not installed on the car.

Tomorrow or Monday I will measure the diameter of the 903 on my 67. It's in very good condition so I hope to get a accurate measurement and will post. I was curious of this later style balancer because in my mind I kept thinking about the 63 type of balancer and wondered if mine is correct.

If the measurements are the same between the two, I am curious what the difference is. I will take the 904 over to the 67 and visually compare the two because the lower pulley is off the engine so I can see pretty good.

[Joe L.]

Re: 1967 327/300HP engine balancer

Thanks Jeff and Joe for the good information. I measured the ID of the new 904 I purchased from GM back in the eighty's at 1.265. This was purchased for my 63 but it's not the original configuration. It's still in my basement not installed on the car.

Tomorrow or Monday I will measure the diameter of the 903 on my 67. It's in very good condition so I hope to get a accurate measurement and will post. I was curious of this later style balancer because in my mind I kept thinking about the 63 type of balancer and wondered if mine is correct.

If the measurements are the same between the two, I am curious what the difference is. I will take the 904 over to the 67 and visually compare the two because the lower pulley is off the engine so I can see pretty good.

Tim-----


Yes, the configuration of the 3896904 balancer is considerably different than the low horsepower 63 balancer. For 1963, the 3896904 is a SERVICE-only balancer which replaced the original style for SERVICE in 1966. However, while not of the same configuration as the original, the 3896904 will SERVICE 1963 applications perfectly.

I'll be very interested in what you find regarding internal diameter of the two balancers. In fact, it will save me the trouble. The problem here is that if there is a difference in ID, it's going to be VERY small----about .001" or less so the measurement has to be very accurate.

The way I see it, there are 2 possibilities for difference between the balancers. First, of course, is the possibility of an ID difference. This is what I THOUGHT for years the difference was. Now, as I say, I'm not so sure.

The second possibility is a "tuning" difference. This sort of difference is not apparent, at all. Just how it's accomplished at manufacture I've long-since forgotten.

As far as I know, with respect to apparent configuration, the '903' and '904' are identical.

[Bill B.]

Re: 1967 327/300HP engine balancer

Process of elimination, 903 balancer is for the 327, the 904 balancer is for the 283. I believe this is correct. They have different diameters and thickness from one another.

The first year for the 327 was in 1962 and on, thus 903.

Please correct me if I'm wrong!

Bill

1961 Black/Silver/Red Int. 283/315 FI
power windows. Frame off 65% completed.
1989 White/hard top/Grey Int. daily driver 167,000 miles

[Joe L.]

Re: 1967 327/300HP engine balancer

Process of elimination, 903 balancer is for the 327, the 904 balancer is for the 283. I believe this is correct. They have different diameters and thickness from one another.

The first year for the 327 was in 1962 and on, thus 903.

Please correct me if I'm wrong!

Bill

1961 Black/Silver/Red Int. 283/315 FI
power windows. Frame off 65% completed.
1989 White/hard top/Grey Int. daily driver 167,000 miles

Bill-----


The GM #3896904 SERVICES all 57-61 (and most later non-Corvette) 283's. However, it also SERVICES 62-65 250 and 300 hp 327's.

As far as I know, the OD of both the 3896903 and 3896904 are the same. I think the thicknesses are the same, too.

[Jeff S.]

Re: 1967 327/300HP engine balancer

The 903 has an OD of 6-1/8".

[Timothy B.]

Re: 1967 327/300HP engine balancer

Took my venier guage and tried to measure the ID of the 903 balancer on my 67. I measured 1.240 but it was difficult to measure accurately.

Picture is of the balancer and crankshaft showing no retaining bolt. The 904 in my basement measured 1.265 so I really don't think this one is tighter and not by .025