So I tore down my spare 153. I was hoping for a "red neck" rebuild, (rings, bearings, valve job), but it doesn't look like this is a good candidate. it already has an .040 overbore and pistons. The tops of three out of four pistons are beat up like it ate something. The cylinders have some taper and are 4 thou over at the largest (3.919), so it would need bored .060 to clean it up. There was a hole in the high end of oil pan and my guess is it died from chronic low oil. Main bearings show some copper pretty evenly and there's some strange wear on the cam. Nylon timing gear looked good, but it broke when I tried to pull it. Must be a trick to that? Also a couple small bits fell out of the block, (not the oil pan) when I had it upside down to push the pistons out. Pics attached. Anybody recognize those little ears? I think my next move is to pull the motor that's in the jeep hoping for something in better shape.
Pretty normal for a used engine. The small pieces you found are ears broken from a cam shaft thrust plate retainer. Cast pistons are not very expensive. The machine work will get you.
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Thanks tlowe. I need all the advice I can get. I pulled the head off the motor in the jeep and found a blown head gasket. I also found .060 over pistons, in excellent condition. So while the motor looks much better inside than the "spare" there is no room for a rebore. My trusted "local", (120miles away) machine shop says maybe 6 months until they would get the spare block bored and decked. So I have a choice to make while I'm waiting. Put in a new head gasket and run it, hoping for the best, (compression was on the low side at 115- 120 prior to the head gasket blowing, the sun sheet says 130 min with 20 max variation), or do a redneck rebuild, (rings, bearings, lap the valves) and hope to get another couple years out of it. I'm wondering about decking it and surfacing the head because of the blown head gasket. That's not big money and a pretty fast turn around. I don't have any good way to check the surface flatness of either. I set my bore gauge to 3.935, (.060 over stock) and did some measuring. Unfortunately I don't have enough experience to interpret the results. All of my prior engine rebuilding experience involved single cylinder 2 stroke motorcycle engines. below is what I found Cyl #1: .0030 over front to back, .0002 over side to side, both taper .0005 more open toward the top until I hit the lip which is about .0020 under the cylinder front to back and .0002 under the cylinder side to side. Cylinder #2: .0015 over front to back, .0020 side to side, very little taper, lip is .0005 front to back and .0020 side to side Cyl #3: .0015 front to back and .0020 side to side .0005 taper. less than lip than I can accurately measure, < .0001 Cyl #4 .0032 and cylindrical with about .0005 taper and .0040 lip
So #1 is .0028 ovaled, and #4 has some more wear than the other three, and more lip at the top. I am wondering what the expectations of accuracy on the rebore would be? And where I'd be if I just ran a ball hone through them all a couple passes and put in new rings?
Just checking in. I got pretty lucky last week and landed a 3.0 mercruiser with only 125 hrs on the meter for a good price. I pulled the valve cover while I was stripping the marine specific parts and it looks like new inside. Compression was 150, 175, 160, 160. I think will should even out once it's run for a bit, (It's been sitting under cover for 15 years). So my plans have changed. I'm going to put a new head gasket in the 153 that's in the jeep, clean up the head a bit and run it through the summer. This will give me time to fab up some decent manifolds for the 181 and I'll swap it in next winter.
I'm pretty sure it's a two piece rear main seal as the serial number is for an '86, and I don't think Mercruiser went to 1 piece seals until 1990? That's important because both of the rear sump oil pans I have are for the two piece seals. It came with a 25lb flywheel which is drilled and tapped for a pressure plate, but it will need to be surfaced as it is currently black paint on the unsurfaced casting. This thing is amazingly clean inside!
I typo'd the earlier post, but corrected it now. What I meant to say was that I'm pretty sure it's a two piece rear seal as they didn't go to the one piece until 1990. Hard to get a good shot of the rear of the block as it's on the stand but maybe you can tell from these
Another question, I have a 120 Mercruiser head that I had boiled, checked and flattened that I'd like to use on the 153 for the summer. I have new valves, springs and seals on the shelf for this head and I was planning to use the keeper plates and shield caps from my spare engine but the plates are worn and the shield caps are cracked, or missing. I cannot find the keeper plates or shield caps online at Rock Auto, Speedway or summit for the 153, and none of the marine parts house seem to have them individually, only as part of a "valve train kit". I can't imagine that these are unique to the 153. Does anyone know what common inline 6 they would interchange with?
Thanks tlowe, How critical are the keepers? Most of them have a little even wear, but the ones that were missing the shields have a little depression where the leading edge of the spring has worn in about .001 The rockers show some wear as well, but nothing I can catch a fingernail on. I was thinking I could smooth that out a little with a piece of 600 grit and some oil. With the hydraulic lifters I am thinking that the absolute overall dimension from the face of the valve to the face of the rocker is not that critical?
I still cannot find a source for the valve spring shields. Every inline chevy I have ever seen has them, every pic of a reman head I can find has them, yet no one sells a valve spring shield for any of the inline engines, What is up with that? Everyone carries them for the 350 V8, are they the same? This is frustrating.
They are listed for the 350 everywhere. Is that the same valve train as the 283/327 motors? I went into the local NAPA today and looked them up under all of the inline six engines. and in the Mercruiser parts book for the 120 and 140, nothing. However, the NAPA guy pointed me toward and engine builder in Hermon, (70 miles away), and I called him. He said he had "all kinds of them". So I'll pick some up when my wife goes to the dentist in Bangor on Monday. Thanks for your help, I'll let you know how it works out.
Just checking in to let you know how it worked out. The engine builder down river turned out to be a good guy and sold me the spring shields and seals out the door for $20. I lapped in the valves and installed the head. Compression with the mercruiser head is 140, 140, 130 and 125. I think I can run with that for this season. I have the manifolds and carb back on and I'm hoping to get the linkages hooked up and antifreeze in today to start it up. I really appreciate the advice I got here!
