as im sure most of you have a saw in previous post my 318 has a knock. i talked to a very reputable guy from work who ran a speed shop and built performance motors for a living for many years with his brother. i had him listen to the noise and he said that for sure it is a bearing in the bottom end. now my question is what would be more reasonable to do. rebuild my bottom end or find a running replacement motor. also what would be cheaper to do i know im looking at about 330 - 350 for the rebuild and can do the work myself so no labor charges. also what can i expect to pay for a running replacement. im just looking to see what you guys think. im open to all offers thanks jeremy
just so you all know the replacement would be used not new

 

Buying used is just buying another mans problems unless you can verify its previous use and maintenance. Rebuilding the lower end, without knowing the condition of the top end, is no better. We can advise you, but you need to do the work. DO A COMPRESSION CHECK! You can usually borrow a compression gauge from the big parts houses for free.

Turning an engine by hand tells you nothing about the internals. You must realize that an engine with low compression and rough bearings can feel the same as an engine with good compression when turned over manually.

 

I do plan on doing 1 but my question is what will it tell me about the top end? Couldnt low compression just mean the rings are shot

 

It can tell you the condition of the rings and the valves if you know how to do it correctly.

 

Wouldnt messed up valves make it not run right? It runs awsome and has great power and lots of torque only problem is bottom end knock

 

Also it doesnt use or burn any oil and only leaks about a quarter qt between changes(valve covers)

 

To answer your question. Valves can leak and cause lower compression. This problem usually happens slowly so that you don't notice the loss of power.

I have given you sound advise. Do what you want with it. Why you seem so opposed to gaining knowledge about your engine puzzles me but it is your engine and you will have to deal with the decisions you make. I wish you good luck with whatever you decide.

 

Im not opposed 2 gaining knowledge a compression test is new to me I thought that only told you about the rings. So how would I no the diference between leaky rings or leaky valves

 

Then you should also do a cylinder leak-down test to see if your valves or rings need work.

 

Do a second compression test on each cylinder if the first reading is lower than it should be. The second test is done after squirting about a tablespoon of oil in the cylinder. The oil will help seal the rings and isolate the bad compression readings to the valves.

A leakdown tester is a device that connects to a compressor and the spark plug hole in the cylinder. In order to leak down test a cylinder, you connect the tester to a cylinder that is at TDC in the compression stroke. The tester applies pressure from the compressor to the cylinder. A gauge then measures how much air is flowing from the compressor to the cylinder (the less air, the better), and the amount of leakdown is meaured in percent. Lower is better. While this is happening, you can then find where the engine is leaking based on where the air is going. Air going out the valves indicates valves that are not sealing. Air going into the crankcase indicates bad rings. Air going into adjacent cylinders indicates a bad head gasket. And air going into water jackets indicates a bad head gasket, cracked cylinder and/or head, or a warped cylinder and/or head. A leakdown test is not necessarily better than a compression test in that it can detect problems where a compression test indicates no problems. But it can tell you exactly WHAT is bad when compression is low. For this reason, a leakdown test is generally used to complement a compression test rather than replacing it.