Crossflow V4 machine work

[Tiderunner18]

My 88spl engine block goes into the machine shop this week. I know one hole will need to be bored and the other three should only need honing. What overbore pistons are available? I've found .020", .030", and .040" so far. Is .040" as big as you can go on these engines?

Also, the guy at the machine shop is recommending that I bore all four holes to the same size with the claim that the engine will be "out of balance". I really don't see much of a problem with one piston being a little bit larger than the others and I've read posts on this forum about people boring only the holes that need it. Any advise?

Is there any other machine work I should have done to the block or heads while everything is apart?

Thanks!

 

[lexkyboater]

Re: Crossflow V4 machine work

I've read in several places (including maybe Seloc/Clymer manuals) that one piston bored larger than the others is not an issue because the oversize pistons weigh almost exactly the same as the standard bore. As long as your ring end gap is within spec on the honed cylinders, it's not an issue. As long as your compression is within 10 - 15 psi on the adjacent cylinders, you're good. Having it close within the other bank is not as important. I have always machined the heads on automotive engines to make sure they're completely flat to ensure good compression and that head gaskets aren't blown - I would assume the same applies to marine engines?

 

[dreamchaser]

Re: Crossflow V4 machine work

Cheers TR,,, myself i have a 1983 115 evirude that lost 1 cyl , Tues I ran around looking for someone who would measure the pots to see if they where ok to just hone out, and rebore the bad one. There arent many shops here that do this job so i ended up goin to a authorized by dealer machine shop for marine motors , 3 of the cyl,s where 0005 over and the bad one needed to be oversized forsure. he also said that the proper way was to do em all for the balance issue ....later that day talked to a auto mech and he advised the same ........ie; balance and blueprint....my 2 cents.......good luck

 

[Dhadley]

Re: Crossflow V4 machine work

There are .064" oversize pistons for that motor. All pistons for that motor, regardless of size, are within weight spec of a new standard piston. There will be no balance issues. This is a two stroke, not a four stroke motor. Most all 4 stroke or auto guys you talk to will tell you it has to be bored all the same. Not so.

Don't go by what the cylinders look like, go by what they measure. The wear and out-of-round tolerence for a crossflow is .004". If it's worn to .002" over and you hone it another .001" (it's very easy to hone over that), then 3/4 of the "normal life" is gone from that cylinder.

The best advise you'll get is to not take it to an automotive shop but rather a marine machine shop. Don't tell them what you want bored and honed -- ask them what needs to be done. Ask for specific measurements.

 

[iwombat]

Re: Crossflow V4 machine work

Even in automotive, it only really matters if the motor is oversquare and high torque. In undersquare motors balance isn't such a critical issue.

 

[dreamchaser]

Re: Crossflow V4 machine work

LEXKYBOATER, Sorry not tryin to highjack ur thread.......DH in my case the .005 wear limit was beyond the max , therefore it was reccomended to do them all , that coming from a 2 stroke performance machine shop which deals with marine work as well ,my misunderstanding......thks

 

[lexkyboater]

Re: Crossflow V4 machine work

Not my thread but if it were, I still like reading all this good info. Thanks I say...

 

[kenmyfam]

Re: Crossflow V4 machine work

Agreed that balance is not an issue with a 2 stroke. Machine what needs it and "tidy up" the other cylinders by honing. It is extremely easy to "over hone" if doing it yourself so be careful