How can I tell a '91 4.3 from a '92 4.3?

[Darkhorse1201]

How can I tell a 1991 4.3 (no balance shaft) from a 1992 4.3 (balance shaft) with looking inside the engine? I have a 1992 Sunbird with an4.3 and I am curious to find out whether or not I have a '91 or a '92? Sometimes they would put a different (as in previous year) engine in a later year boat (due to supplies on hand) and I need to know. Anyway of identifieing them from the outside? Perhaps someone knows of a website where I can decode the ser.#. Thanks in advance.<br />Yay - spring is here - off to the beach!!!!!!

 

[mkast]

Re: How can I tell a '91 4.3 from a '92 4.3?

Get the casing number off the block or heads.

 

[Bondo]

Re: How can I tell a '91 4.3 from a '92 4.3?

My sources tell me the balance shafted motors were Introduced in Mid-year 1993.......

 

[bruceb58]

Re: How can I tell a '91 4.3 from a '92 4.3?

I have seen both 92 and 93 quoted as the start of the balance shaft.

 

[bruceb58]

Re: How can I tell a '91 4.3 from a '92 4.3?

1992 WITH BALANCE SHAFT: The L35 balance shaft engine was introduced in ’92, so the block was modified to make room for it above the camshaft. The lifter retainer was changed to the tunnel design because of the balance shaft; it had two bolts on each side instead of the two in the middle.<br /><br />There were two versions of the balance shaft blocks in ’92. The "first design" block had a needle bearing on the back of the balance shaft that was lubricated by the oil mist from the valley. The "second design" had a sleeve bearing that was pressure fed through an additional drilled passage in the back of the block.<br /><br />All of the 1992 "first design" (c/n 10105903) and "second design" (c/n 10224834) blocks were missing the two bolt bosses, one on each side, that were used with the reinforcing struts for the automatic transmission on some of the ’93 and later applications, so they can only be used in ’92. Be sure to double-check the 10224834 "second design" blocks, though, because some of them came with the strut bosses in the later years so they can be used for the ’93s and ’94s.<br /><br />1993-’94 WITH BALANCE SHAFT: Things got more confusing with the balance shaft blocks in ’93-’94. All of these engines have to have the two extra bolt holes for the strut bosses and 10 bolt holes for the tin front cover. See photo. There are five castings that may or may not be right:

 

[bruceb58]

Re: How can I tell a '91 4.3 from a '92 4.3?

Apparently there are non-balance shaft motors until 1994. Here is info for pre-balance shaft:<br /><br />1987- ’94 WITHOUT BALANCE SHAFT: In 1987, a roller lifter cam was installed, so the block was changed again. Two bolt bosses were added in the middle of the valley for the lifter retainer that kept the rollers properly located on the cam and perpendicular to it. This same basic block was used through ’91 for everything, and in ’92 through ’94 for all of the engines without balance shafts except for one small difference – some of the blocks came with four bolt holes for the tunnel style retainer beginning in ’92. There were several different castings used, including the 10105867, 10172756, 14099073, 14093683 and 10066011 with the two-bolt retainer, and the 10172756, 14099073 and 10066061 blocks with the four-bolt retainer.

 

[Bondo]

Re: How can I tell a '91 4.3 from a '92 4.3?

I was going by the Bam, Mercruiser parts Look up........<br /><br />The Balance shaft motors come into the listings in the 93/95 listings,.....<br />'Course,... They go by Serial #s,...... So, it's hard to pin down a Year............<br /><br />I don't know where Bruce got His Info,....... But it's Better than Mine.........

 

[Darkhorse1201]

Re: How can I tell a '91 4.3 from a '92 4.3?

Thanks guys. So basically according to Bruce (great info and big thanks by the way!) if the block has casting # 10105903 or # 10224834 its a balance shaft and any of the other casting numbers are a non balance shaft? Thanks

 

[I/O WALDO]

Re: How can I tell a '91 4.3 from a '92 4.3?

Does the balanced engine's timing cover have a hump on the top of it to clear the b.shaft?