1993 Johnson V4 rebuild piston help

[jammer729]

Hello guys, I'm new here and could use some help. I am attempting my 1st rebuild on a 93 Johnson 90hp V4. I have torn maybe 15 apart but never put one back togather yet. I feel confident I can do it. Anyway here is my issue. I have a block that needs to be bored out and I have 4 good .030 pistons to use so I plan on having the block bored .030 over. Well I know 2 of the pistons are Sierrra pistons and not sure of the other 2 but they are stamped 030 on top. When I mic them up the sierra pistons are about 3.519 and .006 smaller OD than the other pair at 3.525? Does anyone know the reason for this and will they work with a standard .030 over bore? Also can I use a standard ring set?
I guess the next question is, if I can use them, would you recomend them to go on the top or bottom cylinders?
Thanks

 

[Haffiman]

Re: 1993 Johnson V4 rebuild piston help

I guess that you have two 'forged' or high-pressure casting and two low-pressure casting (Sierra) pistons.
The difference in diameter has to do with difference in temperature expansion.
Personally I'm not in favor of mixing manufacturer when it comes to pistons. However what is the most important is if there are any weight difference between them?
You need to use 0.030 OS ring sets.

 

[dazk14]

Re: 1993 Johnson V4 rebuild piston help

You need to use 0.030 OS ring sets that fit each specific piston you have.

You need rings that will specifically fit a piston.

I wouldn't put a motor together with pistons that are off .006. Maybe match the 2 best pistons with 2 new.

Are these used pistons? Since it sounds like you need rings, it isn't that much more to just new pistons. Vertex would be my 1st pick, but I believe Pro-marine is the only importer I'm aware of. There's plenty of piston options and you may be able to go only .015/.020

WSM and others have a coated hyper-eutectic that only runs around $50 ea.. That what Mar-Fab usually uses in their rebuilds.

You should track down boobie, he can get what you need.

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

The pistons are used. I measured the rings and they are the same on both pistons. The 2 better pistons are the ones I don't know what brand they are so will be hard to match. Plus being my 1st build I don't want to stick to much $ into this in case I blow it up my doing something wrong. $50 a piston is fairly cheap and might consider since rings seem to be around $20. If I succeed I will surely use new stuff on future builds. I weighed them up and they are really close (within a few grams) so that shouldn't be an issue.
So I know the sierra pistons are cast so could the other (larger ones) be forged? From what I read I thought the forged pistons were actually smaller than cast? Or an I backwards?
I was planning on using 1 matched set on the top and the other match on the bottom to limit any balancing issues.

 

[emdsapmgr]

Re: 1993 Johnson V4 rebuild piston help

I'm with Haffiman. I wouldn't mix differrent pistons in a powerhead. Your machinist must make allowances for the expansion rates of various manufacturers' pistons. You are asking for trouble if you mix two different types that may be of two sizes. Not to mention the potential differences in weight.

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

I agree but I am somewhat confused at the same time. I have heard and seen many of these motors rebuilt with different size pistons. My machineist said they only bore bad cylinders and hone the good ones, so if 1 or 2 cylinders are good, they told me to re-ring those and only buy the pistons needed. In that case many rebuilt motors out there have different size pistons in them. My block has 2 scored cylinders, but figured since I have 4 pistons just have all 4 bored out. So if 2 cylinders are good should I re ring the stock pistons and use the 2 better .030 pistons? Or is this not right either, because being .030 bigger they have to weigh different?

 

[dazk14]

Re: 1993 Johnson V4 rebuild piston help

In theory all over-sized pistons will weigh the same, hence it is no problem running different sized bores. But - it must be checked.

Why don't post some good pics of what you have there. Pistons do wear. I can appreciate you're trying to minimize your downside.

What are you being charged a hole to bore/hone AND chamfer the ports?

To answer your forged piston question, the older Wiseco's were approx. same size as stock - which created a problem since the forged pistons expand more. Wiseco now supplies pistons that are slightly smaller than stock, so they fit perfectly when warm in a factory dimensioned bore. Even with that, some builders go a mil or two oversize on the bore to prevent sticking a piston from owners that can't follow instructions.

There are many builders that wouldn't think twice about using various brand cast pistons, presuming the weight is the same - but they would want know who makes each piston.

Modern pistons are often cam ground which means they are not round and will indicate different diameter dimensions - depending on orientation. There can also be taper, the crown will be narrower than the skirt, because the crown will expand more in use...

See why it gets a little more complicated in a quality rebuild. To simply put together a solid runner, you may have adequate materials there.

Amongst other reasons, I don't mix forge pistons with cast simply because forged tend to rattle when cold and at low rpms and hearing a rattle every 4th firing is not good advertising.

 

[emdsapmgr]

Re: 1993 Johnson V4 rebuild piston help

You have heard correctly. You can mix pistons of various bore sizes in one engine. A .030 over piston can be mixed with three standard-as long as they are all from the same manufacturer. Each manufacturer makes their oversize pistons so that they weigh the same as the stock pistons. Theoretically, these pistons are all made identically (except for bore) and will have the same expansion rate when running in a block. The concern regarding your opening comment was that you have pistons from two manufacturers (different manufacturing processes will yield different expansion rates when heated up.) And they are different dimensional sizes at that.

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

Why don't post some good pics of what you have there. Pistons do wear. I can appreciate you're trying to minimize your downside.

What are you being charged a hole to bore/hone AND chamfer the ports?

The machine shop charges $60 per hole to bore and not sure about honing and chamfering? I was just figuring $240 complete. I took some pics and will try to load them. The 2 on the left are the sierra pistons and actually have very few hours on them. The 2 on the right still had over 120 psi compression before I pulled it apart.

 

[emdsapmgr]

Re: 1993 Johnson V4 rebuild piston help

I'd hate to see you overhaul your engine and not fix the problem that caused the original piston damage. There is something definitely going on with two of those pistons. Are they both on the same side of the block? Have you pulled the head cover off the see if there is any debris inside which would affect coolant flow. Have you torn into the carbs to check for debris in the jets that feed the two low compression pistons? Are any of the water bypass rubber deflectors out of position in the block-that would disrupt water flow around those piston's cylinders?

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

The 4 pistons are 2 sets were from 2 different motors which both had overheated, and the block I am rebuilding lost a ring, or I do have another block I might use from a 94 evinrude that someone forgot to add oil? I was going to let the machine shop decide.

 

[Faztbullet]

Re: 1993 Johnson V4 rebuild piston help

The ones on the left do not look like Sierra pistons.....

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

The ones on the left do not look like Sierra pistons.....

They are both stamped 18-4100 and 030 on the face of the piston and when I look that up it is a sierra part #.

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

What are you being charged a hole to bore/hone AND chamfer the ports?

Is $60 to bore a cylinder average?
Is there somewhere the block can be sent and bored cheaper?
Or does anyone know of somewhere in Wisconsin that is cheaper?

 

[dazk14]

Re: 1993 Johnson V4 rebuild piston help

Is $60 to bore a cylinder average?
Is there somewhere the block can be sent and bored cheaper?
Or does anyone know of somewhere in Wisconsin that is cheaper?

1- A little high, but quality it the most important factor if your not doing a lot of volume.
2- Yes, but you do add shipping ~$25 each way for a V4 crossflow.
3- post a separate topic.

It may just be the lighting, but your left most pistons appear to have some erosion.
If your 2 stock bores are good, I'd rather see you get 2 new stock pistons and $15x2 honing.

I misspoke earlier - although boobie may be able to help you.. Your going to need gaskets, maybe bearings, maybe pistons.
Track down Faztbullet. He can get what you need at good prices and can also handle CORRECT piston fitting and machining.

 

[jammer729]

Re: 1993 Johnson V4 rebuild piston help

Thanks for the info. I'll see if I can find another machine shop within driving distance. These guys do good work but don't do alot of boat motors.

 

[Sprky]

Re: 1993 Johnson V4 rebuild piston help

$50 a hole is what we charge. Find someone who can fit the pistons not just finish everything to the same dimention...... Have the cylinders bored to give the clearance you need for each piston.


Chris

 

[dazk14]

Re: 1993 Johnson V4 rebuild piston help

Thanks for the info. I'll see if I can find another machine shop within driving distance. These guys do good work but don't do alot of boat motors.

Since they don't do a lot of outboards, you may want to find someone that does - it's a different animal. The auto shops are fine for throwing a head on a belt sander (resurfacing).