90 HP Chrysler . High compression wont allow the motor to turn?

[Andreea]

Hi
Nice to meet you.
i just replaced the head gasket in my '75 in my 907 BB outboard Chrysler. After reinstalling, with a new battery ( 900 amps cold crank) , the motor won' turn fast enough to start. Removing 1 spark plug will make things better, removing all 3 spark plugs will make the motor turn properly. Is it possible that the compression of the motor is so high than will push against the pistons not allowing the motor to turn? Is there a valve somewhere that is supposed to open during initial start of the motor?
I would like to thank you for the attention .
Thank you
Dragos

 

[jerryjerry05]

Usually if the starting systems good and it won't turn the motor over??
Then the compression on one or more cyl. is low.

Do a compression test and post the results.

Check the starter(clean) and load test the battery, check the cables for weak spots or bulges.
A battery with a bad cell can still read 12v and be bad.

Also if the bearings are dragging or the lower unit is locking up it will do the same thing.

 

[Andreea]

Thanks a lot. This forum is amazing and I have tons to learn !
The battery is brand new. The motor turns perfectly with the spark plugs removed ( no compression build up inside the cylinder). Once I add the spark plugs the starter has a hard time turning the motor for the initial start. As you say I will check the cables , I will clean the starter ( brushes ? ) . I cant to a compression test ( dont have the gauge yet) but I think that a low compression will let the system to turn easyer 9 correct me if I am wrong, I am very new at motor maintenance).
Thanks a lot

 

[kbh121956]

Rent a compression tester from AutoZone. As Jerry stated one for more cylinders with low compression and the starter will drag. Pull all the plugs when doing the test and post results.

 

[Andreea]

Thank you. Will do...

 

[blackd]

My guess you will find the starter dirty/defective/poorly connected. Occasionally, the starter solenoid or relay will go bad, but I've found that to be much more rare than the starter.

Believe Jerry about the bad compression in 1 cylinder.

 

[kbh121956]

Andreea, if you don't know how to do compression testing, there are video's showing how it is done on youtube.

 

[Andreea]

Wow guys , you are amazing
Priority - compression test ( how can it be corrected if bad, low readings ?)
- clean brushes on starter .
I will keep updates here and I hope I am not ( too ) annoying

 

[jerryjerry05]

You wrote

I think that a low compression will let the system to turn easyier 9 correct me if I am wrong,​

"

Yup your wrong, I know it doesn't seem right but it's true.

On my 88 85hp If the compression dropped lower than 10-15 # in one cyl? The motor did the same thing as yours.

Your problem could be the starting system?? Maybe not??
Do the compression test and post the results???

These motors have high compression ratio's.145-165#
If one drops it makes it harder to turn.

Now if you had a v-6 Johnson the comp is much lower and easier to turn with a bad cyl.

 

[Redbarron%%]

When you spin it over with the plugs out do you happen to get water out of one or more cylinders?
Water in a cylinder will give very high compression and indicates other problems as well.

 

[Andreea]

Thanks. I am working on doing the compression test. There is no water getting out the cylinder.Thanks again. The way I see things:
1. The power supplied to the system is not enough ( new battery, cleaned up all the connections and checked all wires. I will try to find new starter-maybe is not strong enough. Can I use a generic much cheaper starter or its got to be Chrysler?
2. The resistance of the moving system is to high ( bad, or I should say uneven compression,bearings resistance....)
Thanks again, if you have any more ideas and if you don' mint too much please put me on the right path , I am lost
Thank you

 

[jerryjerry05]

You have to do a compression test and find out if that's the problem????
I gave you all the answers in my first post.


Bad starter, weak battery, bad connections, bearings in the lower unit seizing,

A new battery can be bad(not likely, but???)
Until the comp test, you can take the starter apart and clean the contacts.
The starter would be the #2 reason it's turning hard.

Check the gear oil and see if there is water in the oil or excessive metal shavings??
Do NOT remove the screw on the side of the lower unit.
The drain plug is on the very bottom and might be hard to find??