Magically increasing bearing diameter

[Richter12x2]

Alright, I give up! We pulled the new GT6 engine apart to clean, it turned perfectly with a tool. All the bearings were in brand new condition, so we didn't change them, just to keep things easy (supposedly). Everything was numbered and matched carefully.

Now, put them all back in in the correct order, lubed and torqued to spec, and can't turn the engine even with a breaker bar. Plastigage'd all the rod bearings, and 3 of them are still what I'd call perfect, at .0015, but the other three are below .001. Nothing was changed! Any ideas on what happened and how to fix? After the last time, I'd just as soon not take the crank to a machine shop, since we don't know which one screwed up the last crank.

 

[MikeP]

Not to sound like a smart a$$, but you sure the bearing halves all went back where they came from?? To me sounds as if there was some slight variation between them and they got mixed up.

 

[Deleted member 8987]

Or you crossed up a rod cap?

 

[jsfbond]

How about the shims on the end of the shaft? That happened to mine on a rebuild.

 

[TR3driver]

Just to cover the obvious, have you tried taking the bearing shells back out, cleaning and reinstalling? .001" isn't very much, just a tiny bit of lint from a shop rag could hold them out by that much. Or if an insert didn't get quite seated into the keyway.

Hopefully you double-checked that the numbers on the rod caps matched the numbers on the rods BEFORE taking it apart. I have found engines with two #4 caps and only one #4 rod.

 

[UmmYeahOk]

Just to cover the obvious, have you tried taking the bearing shells back out, cleaning and reinstalling? .001" isn't very much, just a tiny bit of lint from a shop rag could hold them out by that much. Or if an insert didn't get quite seated into the keyway.

Hopefully you double-checked that the numbers on the rod caps matched the numbers on the rods BEFORE taking it apart. I have found engines with two #4 caps and only one #4 rod.

I'll respond for him. I personally saw that each rod and rod cap had numbers carved into them, and yes they were all installed in order before the tear down. (no extra #s or anything) I don't know if that means that it had been rebuilt before. I would suspect not since I was told that it was a low mileage engine.

When he could not turn the crank I witnessed him take apart everything a second or third time, clean everything, even tried polishing them himself in the off chance that .00001 extra would cause this issue.

Hopefully it is just something quick and easily overlooked like the other above mentioned possibilities.

 

[PeterK]

Did you have the big ends of the rods trued to round at the machine shop?

 

[UmmYeahOk]

Did you have the big ends of the rods trued to round at the machine shop?

we havent taken this to a machine shop, and are avoiding doing so a all cost..

Are you talking about our original motor? Cause those are .020 and as far as we know are fine (since we can't get beyond the cracked main cap issue)

 

[bgbassplyr]

Un-torque all the rods and mains, not loose, just not torqued.
Will the engine move now? If it will:
Torque center main, still turn?
Torque rear main, still turn?
Continue in this manner with mains and rods until you find the one that is binding.

 

[dklawson]

I agree with Jim. Tighten them one at a time to locate the problem bearing(s). I also agree with Randall that it doesn't take much in the way of lint or a spec of dirt behind a bearing shell to close the gaps up.

 

[Richter12x2]

Un-torque all the rods and mains, not loose, just not torqued.
Will the engine move now? If it will:
Torque center main, still turn?
Torque rear main, still turn?
Continue in this manner with mains and rods until you find the one that is binding.

Oh I checked already, it's 2, 3 and 6 that are binding. I might have suspected that maybe I got one bearing mixed up, but I doubt I got three out of order. With the rod bolts untorqued, it turns fine with a little drag.

 

[Richter12x2]

I'll check again tomorrow, and pull them all off. Everything seemed really clean, but I'll get out the digital caliper and take some readings and see if I can figure out what's going on.

 

[Richter12x2]

How about the shims on the end of the shaft? That happened to mine on a rebuild.

The ones that set endplay? I've got one on the inside and one on the outside, and they're both the same thickness. Or is it a different one?

 

[dklawson]

If they are the same thrust washer "shims" that were in there before, it is unlikely that they will have contributed to anything... particularly since you now know the problem lies with rod ends 2, 3, & 6.

 

[UmmYeahOk]

I know its been a while, but I felt that I should post in case someone else should have the same issue.

After my husband gave up and told me that we'll have to find ANOTHER shop, and have pay them to build my 2nd engine (which from what we inspected, had nothing wrong with it) Since it was my engine, and my money, I stared at the block for a while. I noticed that two of the rod caps were facing the other way (the factory part numbers were facing opposite of the others.) I thought that maybe there could be two things wrong. Either 1) the caps are backwards, or 2) the pistons are. I read up, and noticed that all the pistons were facing the same way (arrows), so that couldnt be it. I then checked this thread and saw that the issue was with 2,3 and 6. I looked, and they were all facing opposite from 1 and 5... ...meaning 4 was also facing wrong. I removed all 4, faced them the other way, and retorqued them down to 46ft/lbs. The engine could now turn!!!

I think what the problem was, is that we mistakenly believed that the position number engraved in the piston rod and cap were done so on the same side of every part. All the rods had 1-6 carved all on the same side. This however was not true for the 1 and 5 caps. So they were all in order, but concentration was given to the engraved number, rather than the factory

Not to sound like a smart a$$, but you sure the bearing halves all went back where they came from?? To me sounds as if there was some slight variation between them and they got mixed up.

Or you crossed up a rod cap?

As quoted above, the answer was given, just misunderstood. Since all the parts had numbers engraved into them before removal, they of course had to be in the right order. We both assumed that was what was meant. Did not realize that could also mean, right order, wrong spot.

 

[HerronScott]

How about some pictures?

Scott

 

[angelfj1]

Niki: So happy you got this sorted out! Good luck

 

[startech47]

The tangs in the bearing must both be on the same side of the journal to prevent the bearings from spinning. You really need to take all of the rod caps off and check this. Probably also the center main cap.

 

[Roger]

You guys are really going through the "Learn by experience" school, aren't you?
Years ago I used to rebuild old engines, like pre-WW2 Austin Sevens. I learned pretty quickly not to take any notice of what was stamped on big ends, but used a centrepop to mark the rods and caps so I knew which came from where and which way round. As long as you don't pop in a highly stressed place this is pretty much foolproof.

 

[TR3driver]

Personally, I prefer to look to be sure the marks are correct before disassembling. Then if something doesn't match, I can both correct the problem, and look to see if some other issue is lurking.

Since it's a pretty good chance I'll be the next rebuilder as well as this one, that saves me having to check next time.