Mercruiser 4.3 1989 Compression

[bluesdude]

I purchased this boat with no history except that it would not start. After going through the systematic troubleshooting, I found that the compression in the cylinders was 80-90 psi and adding oil to a cylinder increased compression to 120. My question is...is 80 psi compression too low for the engine to even start or do I continue looking?

 

[Bondo]

Re: Mercruiser 4.3 1989 Compression

That motor Really Needs a Rebuild or Replacement,........<br /><br />But,... It should kick over,+ Possibly Start........

 

[waterone1@aol.com]

Re: Mercruiser 4.3 1989 Compression

From your compression test it sounds like you have bad piston rings. What do the spark plugs look like, are they fouled with oil ? I agree with Bondo, it should still start, but only if the plugs are clean.

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

The plugs are new, don't appear to be firing and are coated with oil; however I have good spark when checking with a timing light. Have a friend coming over tommorrow with equipment to do a pressure test. Thanks guys.

 

[Don S]

Re: Mercruiser 4.3 1989 Compression

With oil on the plugs and low compression that came up when oil was put in the cylinders, you don't need any more tests, you need an overhaul.

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

Started tearing into the engine. Decided to check valve timing first and timing marks aligned. Pulled distibutor cap and rotor was 180 degrees from #1. When I checked with a timing light earlier, timing was around 8 degrees BTC as spec. What is going on???

 

[Don S]

Re: Mercruiser 4.3 1989 Compression

The distributor was put in and the wires put on the cap wherever #1 came up. It has absolutly nothing to do with your compression problem.

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

I now have the engine stripped down to just the short body block and oil pan. The Seloc manual says that the outboard drive must be removed before the engine. There is about 1 foot of clearance in front of the engine to manuver. Will the engine not just disconnect from the bell housing and pull out and up?

 

[waterone1@aol.com]

Re: Mercruiser 4.3 1989 Compression

To answer your question, yes, if you can support the weight of the engine, it can be slid forward and pulled. You need to remove the drive prior to re-installation of the engine to check alignment, so why not just remove it now....it will make things easier.

 

[Don S]

Re: Mercruiser 4.3 1989 Compression

You put the shifter in forward, remove the cross pin for the trim ram, remove 6 nuts and pull the drive off. 5 to 10 minute job, and a lot easier than trying to remove the bellhousing bolts. Plus you don't take a chance of damaging that $300 coupler that you have to remove the engine to replace.

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

Block and heads are now in the machine shop. Outdrive is hanging on a cherry picker.Spent most of the day cleaning out the water jackets on the exhaust manifolds; they were totally clogged. Any tips on the re-install. The alignment tool is expensive. Is there a better way to do it?

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

Block and heads are now in the machine shop. Outdrive is hanging on a cherry picker.Spent most of the day cleaning out the water jackets on the exhaust manifolds; they were totally clogged. Any tips on the re-install. The alignment tool is expensive. Is there a better way to do it?

 

[Don S]

Re: Mercruiser 4.3 1989 Compression

If the manifolds and risers were plugged up that bad, forget cleaning, replace them. All that stuff that plugged them is rust. Next will be a hole that allows water into your engine and you then have a dead engine.<br /><br />Yes the alignment tool is expensive, so are manifolds, risers, and engines and drives and..... <br />"is there a better way" ...... NO.<br /><br />BOAT = Break Out Another Thousand

 

[waterone1@aol.com]

Re: Mercruiser 4.3 1989 Compression

"alignment tool is expensive" ....not sure where you have checked, but go to www.mercstuff.com If you still think that is expensive....have you priced gas lately ?

 

[cslaufer]

Re: Mercruiser 4.3 1989 Compression

your compression should be around 160psi

 

[bluesdude]

Re: Mercruiser 4.3 1989 Compression

Rebuilt engine is in and running great. Thanks guys