90hp V4 oversize piston clearance?

[celman]

Hi!

Anyone know, how much is piston skirt - cylinder wall clearance? I have Evinrude 90hp V4 crossflow motor. I have GLM (#24034) .040 oversize pistons. That motor model is rare here in Finland and machining shops didn't find right clearances in their books for crossflow motors.

Sorry my bad English.

 

[F_R]

Re: 90hp V4 oversize piston clearance?

Hi!

Anyone know, how much is piston skirt - cylinder wall clearance? I have Evinrude 90hp V4 crossflow motor. I have GLM (#24034) .040 oversize pistons. That motor model is rare here in Finland and machining shops didn't find right clearances in their books for crossflow motors.

Sorry my bad English.

Um...what year is your 90hp? The 1964-65 is .0045-.006 (inches), but I suspect you are speaking of a newer motor?

Your English is probably better than mine. I speak a mixture of English, Yankee, and Southern Redneck.

 

[billy4hp]

Re: 90hp V4 oversize piston clearance?

Hi!

Anyone know, how much is piston skirt - cylinder wall clearance? I have Evinrude 90hp V4 crossflow motor. I have GLM (#24034) .040 oversize pistons. That motor model is rare here in Finland and machining shops didn't find right clearances in their books for crossflow motors.

Sorry my bad English.

I would contact the manufacturer to get the appropriate piston clearance. If it's not an OEM piston, it's not uncommon for an aftermarket piston to require different clearance due to a non-OEM cam cut on the skirt of the piston...

JMHO...

Billy

 

[celman]

Re: 90hp V4 oversize piston clearance?

Um...what year is your 90hp? The 1964-65 is .0045-.006 (inches), but I suspect you are speaking of a newer motor?

Motor is 1990 year. In GLM site is, that commonly clearance is 0,0007-0,0009", when use cast pistons. That is too little clearance in my opinion.

Thanks for informations.

 

[celman]

Re: 90hp V4 oversize piston clearance?

I asked that clearance from GLM company and they email me: "The pistons are o.e. replacements you can use the spec. in your service manual".

So anyone know o.e spec, for that motor? I have one repair manual, but clearance isn't marked in the manual.

 

[Dhadley]

Re: 90hp V4 oversize piston clearance?

What they're saying is that it's best not to try and measure the piston. They are cam ground, tapered and barrel shapped. Very hard to measure accurately. You're much better off, since they use OE specs, to have the machine shop hold to a specific finished bore size.

The finished OE standard bore size for a crossflow 90 is 3.5005-3.501". Add your oversize to that and you'll get 3.5405 to 3.541" for your finished bore size. If your shop is used to boring outboards they should be familiar with that process. If you're using an automotive shop that's not used to boring outboards you'll probably end up with a motor that's too tight.

 

[celman]

Re: 90hp V4 oversize piston clearance?

What they're saying is that it's best not to try and measure the piston. They are cam ground, tapered and barrel shapped. Very hard to measure accurately. You're much better off, since they use OE specs, to have the machine shop hold to a specific finished bore size.

The finished OE standard bore size for a crossflow 90 is 3.5005-3.501". Add your oversize to that and you'll get 3.5405 to 3.541" for your finished bore size. If your shop is used to boring outboards they should be familiar with that process. If you're using an automotive shop that's not used to boring outboards you'll probably end up with a motor that's too tight.

Thanks a lot! That is only way how get right bore diameter, when I think that. So "clearance" is 0.0005"-0.001". They tell in the GLM site, how much bigger must be bore diameter vs. piston diameter. I asked wrong way that information But I don't know why they didn't ask in machining shop that bore diameter, only clearance.

Thanks to all answers!

 

[Dhadley]

Re: 90hp V4 oversize piston clearance?

That isn't the skirt to wall clearance, don't say that to the machine shop. You'll end up with a motor that's way too tight.

All they need to know is what the cylinder bore size should end up at when it's done and cooled to room temp. The clearance is built into the piston. Don't worry about measuring the piston, is not that easy. Have them concentrate on a specific bore size at room temp. A good marine machine shop will be very comfortable doing it this way. An automotive shop will not and will most like mess up the job.

 

[celman]

Re: 90hp V4 oversize piston clearance?

That isn't the skirt to wall clearance, don't say that to the machine shop. You'll end up with a motor that's way too tight.

All they need to know is what the cylinder bore size should end up at when it's done and cooled to room temp. The clearance is built into the piston. Don't worry about measuring the piston, is not that easy. Have them concentrate on a specific bore size at room temp. A good marine machine shop will be very comfortable doing it this way. An automotive shop will not and will most like mess up the job.

Yes, I understand that bore diameter must be 3,540 (piston size) + 0,0005"-0,001". And understand, that isn't skirt to wall clearance.

 

[Dhadley]

Re: 90hp V4 oversize piston clearance?

That is correct!