Engine: ROD BEARING HELP! and PlasticGuage

[Gregor]

Don't laugh, my first time at rebuilding an engine. I am working on a 6 cyl 170 lark (1961) engine. I don't like the looks of the rod bearings even though the journals on the crank look good.
When I use plastic guage, I realize it will tell me what clearance I have on the rod bearings. How does this translate to tell me what size bearings to buy? I do not have a mic to mic the journals. Another words is Plastic Guage tells me (as an example), .001 or .003, whatever, I realize that is the clearance of what I have, but what should I buy to replace them? The same?

Thanks for not laughing, at least I didn't hear you!!
Gregor

[Mrs K Corbin]

I'd pull the crank and go to a Decent machine shop.... You'll get an idea if the crank needs turned in any way..
They should be able to mic it and determine if the journals are out of round/tapered as well....
They should also be able to help you order the proper bearings if needed.

[jackb]

tread softly grasshopper..... and I'm no expert, but here's my advise: don't rely on this group here to rebuild your engine or advise you of the same. Tho there appear to be several folks on the forum that know what they're talking about, its another thing to have them looking at your engine in your garage, or wherever it is right now. I foresee another 20+ questions for a newbie to ask experienced folks here, but you need someone with their hands on the engine, or better yet, take it to their or someone else's shop for the important decisions that a good rebuilt (freshened) engine deserves to be reliable for another 5K miles .....or more.....GL In the same vain, I wouldn't want anyone's rep to be questioned if "you", the newbie doesn't follow or ask the pertinent questions...... and if I were that someone who could advise you properly going forward with your project, I wouldn't want to place myself in that position...especially if it were my livelihood....

[rusty nut garage]

We won't laugh no dumb questions here. If you've never rebuilt an engine, it would be best if you had a in person mentor who could walk you thru this. If your a better then average shade tree mechanic you can probably do it yourself.
1. Get a STUDEBAKER shop manual. These manuals are very well written. See http://www.studebakerparts.com for all your manuals and parts needs he's my favorite vendor.
2. Take the block, rods crank cam, to an experienced machine shop for measurements and inspection. Use the plastigage on your final assembly to check clearances.

Don't laugh, my first time at rebuilding an engine. I am working on a 6 cyl 170 lark (1961) engine. I don't like the looks of the rod bearings even though the journals on the crank look good.
When I use plastic guage, I realize it will tell me what clearance I have on the rod bearings. How does this translate to tell me what size bearings to buy? I do not have a mic to mic the journals. Another words is Plastic Guage tells me (as an example), .001 or .003, whatever, I realize that is the clearance of what I have, but what should I buy to replace them? The same?

Thanks for not laughing, at least I didn't hear you!!
Gregor

[Mike Van Veghten]

First thing, was the engine running while in your posession ? Was it running well, no nasty sounds from deep below..?
On the backside of each bearing shell there should be a number stamped in it. It might be VERY fine, but it'll be there. Such as...std., .010, .020 etc.
This will tell you "that" bearings size.

IF...you have the correct sized Plastigage (there are several sizes), then this should be close to telling you if you have the correct sized bearings. You say that the bearings are bad. Depending on what you mean by "not liking the looks" means...the plastigage might "not" fill the gap. and you'll need the next size larger.

My advice is that of Mrs. K. Take the crank out and have a shop measure it for you. You may have to do some sweat talking to them...but give it a try. This is the only way of really knowing what the diameter is.
Also, ask them to check and make sure the journal is still "round".
Might be a better thought....just take the engine to a reputable shop and have them rebuild it. Normally less headaches this way.

Good luck.

Mike

[greyben]

To answer your question, Remove one of the bearing inserts and check on the back. It should have the size stamped, i.e. std, 010, 020, or 030. If it had an older rebuild it might even have .001 or .002 stamped. These smaller undersizes were used back then to compensate for minor crank wear on inexpensive rebuilds. Make sure all the sizes match. Occasionally an engine would spin a bearing and only one journal would be turned.

I commend you for undertaking the work yourself. A lot of engines were rebuilt back then by amateur mechanics. It's a worthwhile experience even if the only thing you learn is not to do it again. A good shop manual is a must, either a factory manual or at least a "Motors" manual.

At least if you do it yourself and something goes wrong you'll know who to blame.

[StudeRich]

All of this so far is good advice, you also need to remember that the Cyl. Heads on these OHV 6's were problematic, so it needs to be Magnafluxed, and Dye Checked for cracks at a Machine shop before investing in a good 3 angle Valve Grind, New Valve Guides and possible surface machining.

You may get by with a Overhaul on this engine after everything is checked.
But a "REBUILD" means EVERYTHING is done including Hot Tanking, Boring and replacing the Pistons, Rings, Cam Bearings, Timing Gears, Oil Pump (Rebuild), Turn Crank, Rods and Mains, Valve Grind, Core Plugs, etc.

[wittsend]

If I'm reading you correctly, you assume that the bearing clearance readings will equate to purchasing bearings that are the correct size. Something like, 'you are reading .004 clearance and the clearance should be .002.' So, you need to buy a bearing that is .002 smaller than the one you have now. Generally it doesn't usually work that way.

Bearings that are in small increment (.001, .002 etc.) are likely hard to find. Also, the wear on your crank journals may be tapered, grooved or oval. The reading may not be identical around the entire journal.

The common practice is to remove the crankshaft, have it measured and then have the journals ground the minimum amount to correct the problem - or to bearing sizes that are available. Typically those bearings are .010, ,.020 or .030 undersized to compensate for the metal ground off the crankshaft. Sometimes .010 will clean up a crank, but only .020 bearings are available (unfortunately).

Lastly those small increment bearing sizes do have a limited and not necessarily ideal purpose. If say a single bearing had issues and the crank could be clean up with fine emery paper then a small increment bearing might be used. It is not ideal, but there are times where the engine can be made functional for a smaller dollar amount.

BTW, when using Plastigage I prefer to put it on the rod side of the bearing. Often when torquing the end cap pressure is exerted downward and can skew the reading. If it is put on the rod side those downward forces won't read. Just be careful to release the end cap by tapping on the bolt for the same reason. Pulling the cap off can skew the readings also (if the Plastigage is on the rod side).

Hope this helps. And, these are not questions that make me laugh. They make me happy that you are wise enough to ask.

[rodnutrandy]

No one mentioned you need to mark your rods to which cylinder they came out , mark your main caps if not already marked and keep the bottom of rod (caps ) on the rod they came off of . If your bearings are std. than you could buy new standard bearings and plastigage the new bearings . that would eliminate the wear on the old bearings . Best advice is get someone who as rebuilt several and has a good history or go to a good machine shop if engine is out . All good advice above !

[Dan Timberlake]

As soon as the rod caps are off I put some snug fitting thinwall vinyl tubing or "bolt boots" over the rod bolts to keep them from getting the chance to knick the crank. Bolt knicks can be carefully eased down with the right tools and technique, but far better and easier is to prevent it happening in the first place.

If I approve of the clearance and taper shown by a full width strip of plastigage I can measure the insert thickness to compare to any insert markings, and my interpretation of them help judge the size to order.

This shows someone using a regular mike near the end of the insert to reduce the interfering impact of bearing curvature.
http://www.fixrambler.com/arts/beari...stdbearing.jpg
The problem with that is the insert ends are by design often 0.001" or so thinner than the hard working middle. That would not prevent determining whether a bearing is 0.010" or 0.020" undersized but a + 001 might be mistaken for standard, etc.

Far better is to use a fancy ball mike in the middle of the insert.
http://www.autocarepro.com/Content/S...0000048938.jpg
A regular micrometer and a ball bearing are a perfectly functional substitute.
http://www.lotustalk.com/forums/atta...g-imag0557.jpg
So is a dial indicator on a decently flat steel plate.
http://www.benchtest.com/images/dial%400.jpg

The nominal insert thickness of the insert used to be in the Clevite bearing book. Might have to work backward from rod big end size and journal size now .

Looks like V8 rod bearing spec is still available.
http://fme-cat.com/overlays/part-det...=#.UvEhuPldUf0

[Stude Rookie]

I am probably wrong but it would seem to me that if you use plastigage you are only measuring half of the clearance that actually exists. There could possible be a built in adjustment on the paper comparison mark but I haven't seen it mentioned.
Stude Rookie

[Dan Timberlake]

Bearing and piston clearance are both "diametral" clearance, and could be found by subtracting the diameter of the journal or piston from the bearing or cylinder ID.
The forces on rods and pistons when in service keep the components pushed one way or the other. Pressurized oil or even much more powerful hydrodynamic oil films don't really have any interest in "centering" the shaft or piston in the bore.
Plastigage pushes the rod away from the journal so there is zero clearance on the other side.

Radial clearance is useful to consider in relatively few instances. One is the clearance and centering of the front main seal relative to the crank when located within a few thousandths of an inch by the main bearings. The assembly process of "centering" of the front cover is attempting to equalize the clearance before securing the cover in place, so when the crank moves a few thousandths this way and that it won't open a gap in the seal or rub the cover .

[Gregor]

Thanks for all the info, I can apply a lot of it and move on down the road. I appreciate it.
Gregor