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G-15, R-16 & H-20 Engine owners

Important technical information is cover here that is critical to proper engine performance of the G, R, and H series engines. A few forum members asked for clarification regarding the differences between early and late 1600 Timing chain sprockets. There are no differences in the timing chains themselves, they are identical. Many roadster owners are aware there was an early “SAE” sprocket set used on the 1500 and 1600 3-main bearing engines. Those engines had SAE and USS fastener threads unlike the later 1600 5-main bearing metric fastener engines. The SAE engines were all the G15 1500 engines and R16 with SN below 40000. R16 engines with serial numbers 40000 or greater are metric, as well as all 5-main H-20 engines.

Nissan changed a few things about the camshafts and sprockets when they switched over to the metric engines: To identify a Metric camshaft is fairly easy. The sprocket bolt is 10mmx 1.5. If a 10mm x 1.5 bolt threads into the cam properly, it is a later “metric” cam. A 10mmx 1.5 bolt will start and then immediately seize in an early SAE camshaft. The reverse test is not good since a 3/8-16 bolt will fit in both cams (it is a sloppy fit in the metric cam), so use the 10mm X 1.5 pitch as a test bolt. Richard Klimmert had the early and late cams profiled and there are very slight differences in lift and duration. Both are on a 109degree centerline. The differences may be due to the emissions modifications for later metric engines. Otherwise the cams are very similar.

As it turns out, Nissan kept the cam sprocket woodruff keyway in the same position relative to the centerline for all the cams (to within a fraction of a degree). This has been verified by multiple measurement methods.

However-this is very important: When Nissan changed to the metric engine, they moved the timing marks and the positions of the teeth by 3 cam degrees (equal to 6 crank degrees) on the cam sprocket and 6 degrees on the crank sprocket relative to the keyways. The metric sprockets are easy to identify because the timing marks are perfectly aligned with a tooth. On OEM and correct aftermarket SAE sprockets, the timing marks are 3 or 6 degrees mis-aligned with the teeth. See the attached photos. The two changes cancel each other out and make the cam timing essentially identical when the correct PAIRS of sprockets are used. This means if the metric sprockets are used as a pair or the SAE sprockets are used as a pair, the cam timing will be the same and correct to within less than one degree. See the photos to identify the various sprockets. The SAE crank sprocket is easy to identify since a tooth is directly over the keyway, where as the metric crank sprocket tooth is more counter clockwise near the left edge of the keyway.

Most importantly, you never want to combine an SAE sprocket with a metric sprocket. The timing changes to the individual sprockets will cause a serious timing error with advance or retard of the cam by 6 crank degrees depending on the combination. This will make the engine run very poorly! The safest bet is to keep metric sprockets with a metric cam and correct SAE sprockets with an SAE cam. Also, be careful when purchasing “SAE” labeled sprockets: One roadster parts supplier is (or was) selling METRIC sprockets incorrectly “marketed” for use with SAE engines and providing a 3 degree camshaft “offset” woodruff key. Since the metric sprocket pair was already the same timing as the SAE pair, the offset key produces a significant timing error! If you used an offset key with this setup, your cam timing is incorrect. (either advanced or retarded depending on which way the offset was installed.) This error can make your engine run very badly and be very difficult to diagnose.

So to summarize, the early SAE cams can be used interchangeably in later engines and vice versa as long as metric sprockets are used as a pair or SAE sprockets are used as a pair.

A few other practical details are worth noting: 1)The early SAE cam sprockets also have a very slightly smaller inside diameter to fit the very slightly smaller nose diameter of the SAE cam. The woodruff key is also 5/32”, not 4mm. 2)The dimensional differences above will make the SAE cam sprocket a “press fit” on a metric cam and require a puller to remove. 3)The metric sprockets are just slightly loose on SAE cams, but probably not enough to cause a concern or timing error. 4)The metric crank sprocket is fairly loose on the 3-main SAE crank nose. For low rpm/unbalanced engines, it may not matter. For high rpm/performance engines, the SAE sprocket is a better fit and choice on the SAE crank. 5) The SAE crank sprocket is a very tight (press) fit on a 5-main crankshaft. Once pressed on a gear puller would be needed to remove it. 6) Nissan shows different part numbers for the camshaft retaining plates, so SAE and metric plates may differ in thickness by a few thousandths. If you are mixing up parts, be sure to verify that the camshaft has some free/end play and the cam sprocket does not bind at all on the plate. This is important since binding would cause a major failure. The factory spec for axial end play is .003-.010”. A little loose is better than too tight! 7)Here are the Nissan part numbers for the metric and SAE sprockets:

  • SAE crank sprocket 13021-32200
  • SAE cam sprocket 13024-32200
  • SAE cam plate 13010-76203
  • Metric crank sprocket 13021–73601
  • Metric cam sprocket 13024–78200
  • Metric cam plate -13010-78201

Again, the safest bet is to keep metric sprockets with a metric cam and correct/genuine SAE sprockets with an SAE cam. Never mix Metric and SAE sprockets in the same engine.

Here is what will happen if you mix up SAE and Metric sprockets: SAE crank sprocket w/SAE cam sprocket – cam timing is correct SAE crank sprocket w/Metric cam sprocket-cam timing is advanced 6 crank degrees Metric crank sprocket w/SAE cam sprocket-cam timing is retarded 6 crank degrees Metric crank sprocket w/Metric cam sprocket – cam timing is correct

Thanks to Richard Klimmert, Curtis Marsten, Stan Chernoff and Dave Premo for their research and contributions to this topic!