Greetings again,
I'm now in the process of pulling rod caps off , inspecting, measuring w/ a micrometer & doing the same with the crankshaft bearings.
Is there any does/dont's, tips, special info, special numbers that I will need to complete this task? Engine is a '98 4.3L vortec with 309k miles.
much appreciated for all info.

 

I use plastigauge to double check before final assembly. It gives a measurement across a a wider part of the bearing. It's cheap, easy, and the peace of mind is worth it.

 

So this is on the 98 4.3 that you pulled out to put into your 1999? You should just keep the same thread for your vehicle instead of making new ones all the time. Difficult to keep track of you if things are spread through many threads.

Big question I have is why you are disturbing the engine bearings - or doing anyting with the bottom end? Does this engine have a problem? Why are you in there? What all have you done to it? Please advise so we can help. I worry that you might be in over your head.

 

I appreciate your concern. The main reason for looking into the bottom end is I quit running the engine with 309k miles ( due to getting my '99 s10 blazer 4x4) and it doesn't run anything like it should). So we figured while the engine is out, put a fresh set of bearings in it. Also I had to replace & shim the crankshaft sensor( in the '98 engine).

 

To do a proper job with micrometers you will need an appropriate set of bore gauges as well, then you may skip the plastigage, else that's the way to go.

As Lesmyer suggested working on the bottom end is quite an undertaking.

If you're still into this there is this guide being very helpful in having a good look at your bearings:
https://www.mahle-aftermarket.com/me...s-brochure.pdf

 

Greetings again & thank you so very much for all the help & info.
so here's another question; is there any particular brand of bearings ( connecting rod / crankshaft) that are better/ or more preferred to use than another? I have noticed that a couple brands are mentioned several times ; EngineTech, Mahle/Clevite, so is there any difference in what is installed?
and again, thank you for any & all help.

 

My engine shop normally uses the Mahle/Clevite. That's also what I have ordered for my build.
They don't like KING.

Clevite are nice bearings, good quality, very precise, good crush and good coatings.

And I fully agree with Lesmyer.

 

I think you need to worry more about getting a reground crank in that 300K motor. Crank kits come with bearings.

New bearings by themselves are not going to live long running on a worn old crankshaft (no matter what kind you buy). Old bearings were matched by the wear between the two. New bearings will only contact the top of the grooves in the old crankshaft. SOP typically also includes resizing the rods and at least checking line bore. You really shouldn't have taken a good running high-mile motor apart (if that is what it was) unless you intended to go through it.

A question...... How are you intending to change bearings out....... with crankshaft in place? or by "spinning" crank in with all pistons/rods in place? or are you removing/reinstalling pistons? If you remove the pistons you will need to at least re-hone the cylinders and install new rings. But then again, it's a 300K mile motor and will undoubtedly need bored with new pistons. To do this you have to hot tank the block and have new cam bearings and balance shaft bearings installed. Then might as well resize the rods. Now you're into the short bock for a lot of cash. It's a slippery slope once you start taking high mile bottom ends apart to freshen them up.

IMHO your best bet at this point (if this was a good running motor) is to spin a crank kit into it with the pistons/rods in place and ignore the rest. Unfortunately spinning a crank in is NOT a job for a novice - it's pretty tricky and easy to screw up by dinging the crank or bearings, or by getting dirt in where it shouldn't be. I predict you are going to need experienced help to get it done and not have a bearing failure. But I think you will probably not listen to my advice and will try to replace just the bearings. That's OK - it's your vehicle. I just thought it needed to be said.

 

Just being honest with you, I listen & take in account not only ur advice, but everyone who lends great advice to me. To answer ur question- yes we plan on replacing them with the crank still in. We didn't figure on removing the pistons since the engine has excellent compression. Side note: I wouldn't need to be going through any of this if I could figure out why the engine in my '99 is so sluggish & weak when it's under a load ( like going uphill. But anyway, I do appreciate your advice.

 

From experience the first question that comes to mind is:

Are your bearings shot at all?

If the bottom is not producing a knock and the bearings look good you can simply put them together again in the exact same location. As long as they are within specs and not damaged otherwise.
If the bearings are scored or show signs of failure an overhaul of the bottom may become necessary to get a good engine.

Sluggish engine on hills can also point to other issues. What comes to my mind is (EGR, ignition misalignment, detonation due to other issues, TPS) you name them. The bottom of an engine being very seldom a problem except if damaging a bearing and then you have to do a proper job on the whole to get it back up running.

Last year we pulled a pair of rod bearings and a pair of main bearings of a 63 Studebaker Avanti because the engine was said to be "rebuilt" but we had no papers for it. Turns out the engine was rebuilt. Bearings were looking o.k. So we put all back together.
The bearings showed little trace of foreign particles embedded in the first layer (soft one) which is meant to do exactly that. Crank had some minor scoring as well.

My engine build had about the same traces. Some foreign particles which turned out to be mainly casting sand and casting particles were embedded, the crank also showed scoring within limits. Could probably have been put back together and held another 80k miles.