Model Year: 1956-1968
Subject: Connecting Rod Bolt Usage
Source: Chevrolet Service News
Date: August, 1968
A new connecting rod assembly incorporating a 7/16" diameter connecting rod bolt is being used in late built Corvette R.P.O. L-88 (427 cu. in., 430 H.P.) engines and heavy duty M4 service engines. Early built R.P.O. L-88 engines and all other 427 cu. in. engines incorporate the 3/8" diameter bolt. The connecting rod nut used on the 7/16" diameter bolt should be torqued to 70 ft-lbs.; the 3/8" diameter bolt nut should be torqued to 45 ft.-lbs.
Due to considerable variance between connecting rod bolt usages, a chart has been included in this article giving a listing of connecting rod applications by model year and by part number.
| Connecting Rod Bolt Usage Chart | ||
|---|---|---|
| Year | Application | Part No. |
| 1968 | ||
| Corvair | 6255636 | |
| 4 & 6 cylinder engines (except 292) | 3892670 | |
| 292 cu. in. engine | 3789421 | |
| 307, 327 & 350 cu. in. engine | 3916399 | |
| 366, 396, & 427 (except Corvette RPO L-88 2nd Design) cu. in. engine | 3862720 | |
| Corvette RPO L-88 2nd Design (427 cu. in., 430 H.P)1 | 3942409 | |
| 1967 | ||
| Corvair | 6255636 | |
| 4 & 6 cylinder engines (except 292) | 3892670 | |
| 292 cu. in. engine | 3789421 | |
| 283, 327 & 350 cu. in engine | 3892670 | |
| 366, 396 & 427 cu. in. engine | 3862720 | |
| 1963-1966 | ||
| Corvair | 6255636 | |
| 4 & 6 cylinder (except 292 engine & 1963 L-6 engine used in K Series Trucks) | 3892670 | |
| 292 cu. in. engine | 3789421 | |
| L6 engine used in 1963 K Series Trucks | 3916399 | |
| V-8 engines (except 348, 409, 366, 396 & 427) | 3892670 | |
| 348 & 409 (except Special High Performance RPO Z-11) | 3732718 | |
| Special High Performance 409 engine (RPO Z-11) offered in 1963 | 3837689 | |
| 366, 396 & 427 cu. in. engine | 3862720 | |
| 1962 | ||
| Corvair | 6255636 | |
| 6 cylinder engines (except Chevy II) | 3836670 | |
| Chevy II 4 & 6 cylinder engine | 3892670 | |
| V-8 engines (except 348 & 409 engines) | 3892670 | |
| 348 & 409 cu. in. engine | 3732718 | |
| 19562-1961 | ||
| Corvair | 6255636 | |
| 6 cylinder engines | 3836670 | |
| V-8 engines (except 348 & 409 engines) | 3892670 | |
| 348 & 409 cu. in engine | 3732718 | |
| 1: Also used in Heavy Duty M4 service engines. 2: For model years prior to 1956 reference Parts Catalog under group 0.623. |
||
| Connecting Rod Bolt Configuration | ||
|---|---|---|
| Part No. | Thread | Torque. |
| 3732718 | 3/8-24 x 2 | 45 FT. LBS. |
| 3789421 | 3/8-24 x 1 29/32 | 45 FT. LBS. |
| 3836670 | 3/8-24 x 2 1/4 | 45 FT. LBS. |
| 3837689 | 3/8-24 x 2 25/64 | 45 FT. LBS. |
| 38623720 | 3/8-24 x 2 1/8 | 45 FT. LBS. |
| 38923670 | 11/32-24 x 1 7/8 | 35 FT. LBS. |
| 3916399 | 3/8-24 x 1 39/64 | 45 FT. LBS. |
| 3942409 | 7/16-24 x 2 1/8 | 70 FT. LBS. |
| 6255636 | 5/16-24 x 1 57/64 | 25 FT. LBS. |
Article ID: 686
Created: August 1, 2014
Last Updated: August 1, 2014
Online URL: https://www.corvetteactioncenter.com/tech/knowledgebase/article/1956-1968-corvette-service-news-connecting-rod-bolt-usage-686.html