Alright, more engine rebuild questions

[Pir0San]

So, I think I might finally dive in and do my engine rebuild. I'm going to utilize the numbers matching block and pistons,but use the crank and rods out of my spare engine. I am not sure if the engine I have in the car right now has the same bearing clearances as the stock block, so I was considering pulling the engine, taking the oil pan off, and comparing the rod and main bearings from the current engine against the numbers matching engine. Would there be a visible difference between oversize bearings and stock bearings? I've read in Wick Humble's book that he recommends using plastic gauge, but I have never used it. Anyone know how to use it and explain it to me?

Also, if the original block didn't burn oil, and the rings were in good condition, do I have to get the block checked out for correct ring clearances, or should I not even worry about it?

Thanks guys, I'm just about ready to take the plunge.

By the way, does anyone in Sacramento, or even on this board, have a Colortune they want to sell for a good price?

[jfairladyz]

Dont use Plasti gauge. The best (and only way IMO) is to use a micrometer to measure internal engine parts. To get a rough feel for the size of something (cross referencing parts) you can use a set of dial calipers. but dont use them for final clearance measurements.

As far as seeing visual difference in the size of oversized bearings: No not while they're installed. Not unless you held them side by side to a standard size bearing to compare which was slightly larger. But at that point the bearings would be free of the engine and they should have their thickness stamped on them so you can just check that. But the best way is to measure the crank journals with a micrometer. Then measure the bores of the mains, and the rods to determine the clearance. That will tell you what size bearings you need.

[Arne]

My opinion - if you are going to go through the work and expense of pulling and refurbishing the motor at all, do it all and do it right. If you don't have the proper professional measuring tools (and most of us don't), take the parts you want to use to your chosen machine shop and have them tell you what you need. If I were going to go this far on mine (and I was planning on it until I bought my parts car with a good motor in it), I would automatically replace all the bearings, probably have the crank polished, the rods checked, new rings properly end-gapped, and either a light hone on the cylinders with the original pistons, or bored over-size with new pistons, depending on the wear in the bore now. Probably a new oil pump, and maybe have the crank/rods/flywheel balanced.

While the head was off, new guides, timing chain kit, and hard intake seats (if they haven't already been replaced). Probably all new valves and springs. Reuse the cam and rockers if they are good, but a new cam oil rail if the cam is not drilled.

The thing is that you only want to do this once, so don't take any shortcuts. If there's any doubt about a part, replace it.

[240ZX]

What Arne said is so true! Regarding doing the measurements on engine components......there is more to it than just mic'ing a part. There are specific areas and measurements from different angles that will provide you with the correct information. So as mentioned, if you do not have the specific tools and experience to do the task....take it to a reputable machine shop that does this work on a regular basis.

Tom

[240ZMan]

Jeremy, I just did a proper rebuild of my L28 this summer, after doing more or less what you are suggesting the summer before. I really thought I could cheap out in a bunch of places but in the end, I was very unhappy with the results (burning oil, poor compression). I'm not suggesting you replace everything, but you should evaluate everything, and replace ALL the parts that need to be. I think this is most important with the bottom end since it's the most work by far to repair. Plus, any time you take the crank out, you should be changing the bearings, so you have that expense again if you have to go back in.

On the top end, I think a good head shop can measure your valves, guides, etc. and help you decide what needs to be machined or replaced. In my case, my valves and seats were all in good condition, and I just needed to have my guides cleaned up and add new seals.

BTW, if you haven't already got a copy, you should get "How to Rebuild Your Nissan & Datsun OHC Engine" by Tom Monroe. You could go crazy doing everything he recommends, but at least you have all the best practices in one place, and then you can decide how much you can afford to do for your particular case.

FWIW, before I did my first "rebuild", I asked on this site for advice and was told what I'm telling you now. I didn't listen, and this story tells the rest.