This one is a little hard to explain — bottom line is MAZDA changed things and never told anybody + did/does not always supply the correct parts !! — in addition to that, if you purchase a NEW front side housing for your 86-88, it will PROBABLY come with the 89-92 casting style!
What you are trying to prevent is having the gasket and O-ring squeezing out of place and blowing the oil (under pressure) into the front cover instead of through the engine. SYMPTOMS of this problem are lower oil pressure at all times, but especially when the engine is hot. A slight “squeeze-out” can give 10-20 lbs at idle, 40-55 at 3500rpm, and drop to 35lbs at 5000rpm. A large “squeeze-out” can give almost zero at idle, and maybe 35-40lbs above 2000rpm.
The summary of all the following (our recommendation – others shops may differ) is:
If you have the earlier front side housing style, assemble the front of the engine with the O-ring, no front cover gasket, (use silicone instead), and maybe a little Hylomar to hold the O-ring in place during assembly (and throw away the white teflon ring that comes in the gasket set). If you really WANT to use a gasket, then use the 79-85 one, which needs to be purchased separately.
If you have the later style front side housing, use the gasket, rubber O-ring, and white teflon O-ring (and we prefer some silicone) — gasket CAN be left out, and use silicone in place of it.
|This is the 86-88 style of casting – note the size of the casting around the O-ring.|
|This is a close-up of the O-ring area of the EARLY casting.|
|This is the 89-92 casting – note how much larger the casting is in the area of the O-ring.|
|This is a close-up of the LATER casting – scale is the SAME as the close-up above!|
|This is the rubber O-ring and Teflon ring.|
|On the LEFT is the gasket supplied with 86-92 gasket sets. On the RIGHT is a 79-85 front cover gasket.|
|Note how much larger the hole is where the gasket goes around the O-ring area.|
|Early casting ready for silicone and assembly.|
|Good shot of how much metal is there for gasket/silicone support on the LATER castings.|
|Later casting ready for silicone and assembly (or you can leave the gasket out).|
|WRONG – this is early casting with teflon ring and 86-92 gasket – the teflon ring will hold the front cover off too far, and notice how there is NO casting to hold the gasket up.|
|Same as above, but shows how little (none!) of the casting will hold the gasket. You can also see how the rubber O-ring sits below the teflon ring.|
|WRONG WAY – this is 86-92 gasket with early casting and no teflon ring. It does not have enough support for the gasket, which will break out and most likely let the O-ring squeeze out.|
|WRONG – here is 86-92 gasket, later casting, and the teflon ring left out. There is nothing to keep the rubber O-ring in place.|
|We hope this page may have been of benefit to anyone assembling their engine, or anyone tracking down low oil pressure with an engine assembled by someone else.|