honda 90 compression

[kenneth m]

I have a 1998 honda bf 90 with 1000 hours on engine. The book say the compression should be 214 psi (which seems high to me) I have 135 to 145 per cylinder. Shooting oil in the cylinders will not bring the compression up past 145 psi. Since all cylinders are so close in the numbers is it possible the valves are bad on all 4 cylinders? The valve lash has been checked twice and is within specs. The engine will run fine, idle ok and run at top speed but it don't have the power it should have. Takes forever to get my 16.6 key largo boat on plane with two people in boat. any ideas???

 

[JB]

Re: honda 90 compression

Hi, Ken.

Welcome to iboats.

Technique and gauge make a lot of difference in measuring compression. On a 4 stroke, for example, it makes a lot of difference that you warm the engine beforehand, have all spark plugs out, use a fully charged battery, turn her over at least 5 times per cylinder and have the throttle at WOT.

We need to know the exact technique you used, but. . .

All cylinders are within 5% of each other, which tells me the engine is fine but the test is flawed.

 

[pvanv]

Re: honda 90 compression

How are you pitched?

 

[kenneth m]

Re: honda 90 compression

Hi, Ken.

Welcome to iboats.

Technique and gauge make a lot of difference in measuring compression. On a 4 stroke, for example, it makes a lot of difference that you warm the engine beforehand, have all spark plugs out, use a fully charged battery, turn her over at least 5 times per cylinder and have the throttle at WOT.

We need to know the exact technique you used, but. . .

All cylinders are within 5% of each other, which tells me the engine is fine but the test is flawed.

I warmed the engine before hand throdles wide open. all spark plugs out. battery charged, cranked at least 7 or 8 times. Is it possible the book compression of 212 is incorrect??

 

[kenneth m]

Re: honda 90 compression

How are you pitched?

The prop is the same one on the boat for the last 14 years. Still can't understand why the compression numbers are so far out from the specs.

 

[JB]

Re: honda 90 compression

You used a different gauge than they did. Your engine is okay. Don't get paranoid about it. There is no way, even in a 4 stroke, that 4 cylinders all go bad by the same amount at the same time.

This is exactly why most makers refuse to specify compression numbers.

 

[multimech]

Re: honda 90 compression

Compression tests can be notorious for not giving you an accurate reading of the engine health. Do a leakdown. You should have no more than 10% leakdown. You see the compression guage "builds" because it has a check valve in it. You could still have valves that are not seating correctly, but will show good on a compression check. I do leakdown on two strokes as well.

 

[Harvey Bergen]

I have a 1998 honda bf 90 with 1000 hours on engine. The book say the compression should be 214 psi (which seems high to me) I have 135 to 145 per cylinder. Shooting oil in the cylinders will not bring the compression up past 145 psi. Since all cylinders are so close in the numbers is it possible the valves are bad on all 4 cylinders? The valve lash has been checked twice and is within specs. The engine will run fine, idle ok and run at top speed but it don't have the power it should have. Takes forever to get my 16.6 key largo boat on plane with two people in boat. any ideas???

Hello Kenneth, when your engine was running well in the past what rpm did your motor operate at? it should with normal load be around six thousand rpm. this is a normal operation. If it does not your prop has to
much pitch. also any barnacles on the bottom of your boat will slow you down a lot. Regards hope this helps. Regards Harvey Bergen.