Rebuilding OLD V4 powerhead

[Droll]

I plan to rebuild my old V4 powerhead. <br />But what happened ?, wrist pins on port pistons got loose and really did some damage to the cylinders , starboard pistons were still good . <br />

<br /><br />The questions to you is:<br /><br />Why did the powerhead fail? I got some theories <br />The thermostat house was repaired by the previous owner ( inserted tube )see pic<br />

<br />Would this repair restrict the water to this part of the powerhead ?<br />Upper/lower seal was worn out,wrong mixture to top/bottom cylinders ?<br />The lower mixture needle on carb was bent ( only the part outside carb? I think )<br />The cam in the distributor were destroyed, had to make a replacement ( worked fine (homemade ), but was later replace by an <br />electronic ignition from an Audi 80 )<br />To high RPM ? , 15-foot boat, prop 10 x 12 .<br />Other things? <br /><br />Other things to consider when rebuilding?<br /><br />I got new bearings / seals org. OMC<br />new gaskets, mainly org. OMC<br />New pistons /rings org. OMC<br />Block will be bored up .020<br />Replacing distributor ( used but whith new points, cond. ,rotor ,belt ) <br />New water pump (whole) ( the old one is still usable with almost new impeller , but…) <br />Rebuilding carb ( new high/low speed needles, gaskets )<br />New rod bolts , ( not yet rodbolt but I will )<br /><br />Still missing some parts but I think I got all those hardtofind parts ,thanks to some people here + Ebay + others.<br /><br />Thanks<br />Arne Kjetil

 

[R.Johnson]

Re: Rebuilding OLD V4 powerhead

Before you get to far into this project you may want to consider the carb. Parts are no longer made for it. Needles and seats you can probably find, but gaskets could prove to be a problem.

 

[Droll]

Re: Rebuilding OLD V4 powerhead

I aready got the the parts for the carb + one extra carb .<br />Only missing some gasket for the mid section, got all for the powerhead + lower unit.<br />Only missing the easy parts + some time to do the work

 

[Joe Reeves]

Re: Rebuilding OLD V4 powerhead

Arne.... The picture of the piston above indicates that the failure (most likely cause) was due to what most mechanics refer to as a "washout".<br /><br />This is caused by faulty, erratic, or non existent ignition. The fuel/oil mixture is constantly being drawn into the cylinder, and since the fuel is the greater portion of the mixture ratio, eventually the gasoline overcomes the oil portion.<br /><br />In essence, the 24/1 or 50/1 mixture is eventually reduced to something like 200/1, 300/1, 400/1 etc.... you get the picture I'm sure.<br /><br />This creates a great amount of friction, the results of which depict the piston above.

 

[Droll]

Re: Rebuilding OLD V4 powerhead

So if I this picture right ,when rebuilding the engine whith a rebuildt distributor up to spec. this engine will run until ....<br />How about the thermostat housing ?,the port cyliders got the smalest hole out ( inserted pipe ) , it got 3 - 4mm increase in the diameter of the input.

 

[Joe Reeves]

Re: Rebuilding OLD V4 powerhead

The thermo hsg should have identical passageways. I don't know if you would have a problem with the one you have or not. I'll check to see if I have one and will get back to you ASAP.

 

[Droll]

Re: Rebuilding OLD V4 powerhead

Already got a replacemet for lower part of the housing ,just trying to find out why it broke down , but thanks .