Standard or Low Octane (Low Compression) Head Gaskets?

[kevin88]

I have an 1974 Evinrude 135 HP v4 that I've been troubleshooting several issues on with the help of this site and now I have a new question. <br /><br />My head gasket on the starboard side started leaking water badly and it needs replaced. When I went to a local marina to order the parts they asked me if I wanted the standard gasket or the Low Octane one and I couldn't answer him.<br /><br />I am thinking that I need the low octane/low compression gasket because my motor has shown signs of pre-ignition. Earlier this year I took it out to the lake and abruptly lost 1 cylinder. The spark plug in the #3 cylinder had the electrode completely burnt off. I replaced that and the motor has run decent since. <br />When starting it kicks at times like a backfire but the timing is correct @4 deg and the problem is not persistant. It also idles badly at times.<br />And last but not least when in the water the maximum RPM I can get out of this motor is 4200 RPM. The boat is a 17 foot semi-tri hull LUND and I am using a 13 X 19 Stainless prop which is what Michigan Wheel recommends for my boat.<br /><br />In your professional opinion which gasket should I use when replacing my bad one(s) and why?

 

[Dhadley]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

The standard gasket should be fine but your motor has some fairly serious issues. You need to start with the basics -- compression test is #1.<br /><br />Theres something going on that isnt allowing the motor to reach the proper rpms. At 4200 youre 1600 rpm short of your target. Thats more than a prop change. We also need to check spark to make sure all 4 are firing and probably clean the carbs. You really dont want to lean out a cylinder.<br /><br />what plugs are you using? Champions only in that motor!

 

[00000dan]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

not meaning to butt in, but what plugs for this motor. someone is barrowing my manual(so cant look up in book) and i need spark plugs???? mine is a 76 135

 

[kevin88]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

I'll have to replace the gasket(s) before doing a compression test. If standard gaskets will do I'll use them for sure because they are a good $10.00 a peice cheaper.<br />The spark plugs on this outboard are L77JC4 Champions on 3 cylinders and QL77JC4 which replaced the one that burnt.<br /> All 4 cylinders are firing normally. I lost 2 power packs before I found the real cause of my spark problem as seen on my other posts.<br /> I've so far replaced the stator, rectifier, power pack, all the spark plug boots, and one coil and it's running the best I've ever had it which is 35 MPH @ 4,200 RPM Wide Open. <br /> I'm about to pull the heads off and inspect them and I've noticed something. The overheat sensor is on the Starboard head under the head cover gasket. Is there any way to remove this without having to replace that gasket as well? It doesn't appear to have a quick connector anywhere in the wire that it can just be disconnected with. Can a quick connector be put on this line without damaging the integrity of the sensor?

 

[ddbyrd3]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

Your temp sensor should have a connector that you can disconnect. Is there a black boot anywhere on the wire? If so slide it up or down and you will expose a twist connector and you can separate the wires.<br /><br />My black boots are real tight to the wire its a chore so slide them down...<br /><br />You should be running QL77JC4 plugs. Gapped at I believe .040<br /><br />Kevin, based on DHadley's advice, when I replaced my head gaskets last week I went with stock, and I run 87 octane fuel.<br /><br />When I did a plug reading after a few WOT runs all looked good.. I would recommend the stock head gaskets...

 

[Dhadley]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

Dan, the (Q)L77JC4 is a good plug for your motor or Kevins.<br /><br />Kevin, while youve got the heads off change the 4 deflectors. The little pieces of rubber hose in the water passages. 322411 is the part number.

 

[kevin88]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

I'll be checking compression and pulling the heads off this weekend. I'll keep you posted on Monday what the results were. <br />I already suspect low compression on at least one cylinder so that leads me to my next question. If the compression is low but there is no visible signs of scoring in the cylinder can I just replace the piston rings without doing a complete tear down and rebuild of this unit? What are my options? Good and bad?

 

[kevin88]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

#1 - 110 PSI<br />#2 - 100 PSI<br />#3 - 110 PSI <br />and #4 - 65 PSI.<br /><br />The surprising thing about these compression readings is that it was the #2 cylinder that had the pre-ignition problem that burnt the electrode clean off the spark plug.<br /><br />I'll be pulling the heads off sometime tommorrow afternoon and I'll report back what I see.

 

[kevin88]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

Well, after tearing the heads off I can see that the #4 piston is going to need replacing. It appears that the piston ring broke and a small part of it came free busting the side of the piston in the process. The ports all look good and the cylinder isn't gouged, though there are a few small scratches. So I have to ask is there a way to replace the #4 piston and rings without a complete teardown?

 

[Dhadley]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

Nope.<br /><br />Even if you did get the piston out, how would you bore that cylinder? Or even clean the block properly?

 

[kevin88]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

I was hoping to avoid taking it down into 1,000 peices. I've had the power head off once before and it wasn't pretty. <br />Thanks for you help Dhadley.

 

[Dhadley]

Re: Standard or Low Octane (Low Compression) Head Gaskets?

Ah-ha! Youre experienced! Very good. This time should be a piece of cake.<br /><br />What wasnt pretty about it?