2 replies to this topic

[fotostars]

OK,
so I have a spare 1.8L (unknown history) that I'm working on. First time doing an engine rebuild. Trying to learn something out of it.
I measured the journals on the crank, they look pretty good.
Main journal: 4.994 cm consistent across the 5 (lower limit of STD spec)
Rod journal: 4.494 cm consistent across all 4 (lower limit of STD spec)

I then measured the oil clearance on the main bearings with the "old existing bearings" with plastigage:
#1 0.0015" , #2 0.0017", #3 0.0014", #4 0.0014", #5 0.0015"

The book says standard 0.0007"-0.0014" but the "limit for service" is at 0.004" ! , so I'm a little over the standard range but far from the limit.
Am I good to reuse the crank as is? What am I leaving on the table?

I haven't measured the rod bearing clearance yet, let's just assume it's ~ the same (i.e. a bit over the standard but far from the service limit).

Thoughts from someone who's got experience with bottom end: Should I just put new bearings in and I'm good to go?

[FTodaro]

I am not a motor builder but i have rebuilt my street 1.8 for the fun of it. I will give you my answer and let’s see what the pros say. Some builders build motors loose intentionally. So if you within the service limit I would think your just fine. When I rebuilt my motor i just replaced the bearings with std bearing and rings. I was not that concerned with the clearance issues it had lots of miles on it but the block, crank and all other parts were in good shape. I would just replace all you bearings and rings with std sized. I did bring the block to a shop and had it dipped and honed for chrome molly rings. It’s been good to go ever since.

I did however know the history of my motor so gave me some confidence in what i was working with.

[dstevens]

My 1.6 was similar and I did rings and bearings. The greatest performance gains will be the head and things to do with air/fuel mixture. Being your first one, I'd get it back together stock and perhaps next time around seeing if someone will impart some of the tweaks they may use on the bottom.

I haven't worked on the Miata in almost a few months but here are some pics from the engine build I did last summer. It's about 15 posts worth, from pulling it to bagging it on the stand after I finsihed where it's been for the last several months.

http://roaddog.com/r...ade-tree-build/