2007 Mercury Pro XS slight tick at idle. Forged pistons.

[Basshead35]

Recently rebuilt Pro XS 250. Wiseco forged pistons. Followed Don’s break in procedure on the break in page which supplements the oem manual. Everything operates great with great performance. The machinist put .001” clearance in addition to the wiseco spec due to overheat and expansion concern on the #6 cylinder. The # 6 cylinder has a slight tick at idle only. Seems to go away after a good run or warm up. Will hear it sometimes and after warms it goes away. Barely give it throttle and no longer hear the tick. I am being told that forged pistons can be noisier than cast. It is definitely piston slap and is affected by temperature or expansion of the piston. Compression is not affected and engine runs perfect performance wise. I spoke with a wiseco rep after the fact and he said if the machinist add any more clearance than it will be noisy and I will think something is wrong. I would like to get some different opinions and maybe Don can weigh in on what he thinks. Have you heard of this and from experience will a little piston slap at idle last longevity wise…? Is it common on forged pistons. Wiseco website also talks about noisy pistons and they added a coating to help quiet the pistons.


Thanks!!
2007 250 Mercury Pro XS
Serial #: 1B492182

[Savage]

Piston slap is never good in motors with sustained high RPM'S. This doesn't help you now, but I would have used stock pistons.

[fuelleak]

Used a lot of Wiesco's in some high horsepower KTM's with great success. So your machinist added a thousands just to #6? If that what you post says then I would have to bet that thousands is making it a bit noisy. It will run fine especially if the noise goes away upon warmup. I dont think we ever had a Wiesco failure if the bores were machined correctly.

[Basshead35]

Used a lot of Wiesco's in some high horsepower KTM's with great success. So your machinist added a thousands just to #6? If that what you post says then I would have to bet that thousands is making it a bit noisy. It will run fine especially if the noise goes away upon warmup. I dont think we ever had a Wiesco failure if the bores were machined correctly.

#6 failed Due to cold seizure. Machinist is old school and seemed pretty knowledgable with outboards and motorcross bikes. He stated that he had others before that had consistent overheat issues within a cylinder. He said one person added a fitting to the block to relieve/drain the cooling water from a cylinder (non optimax) and it cured the over heat problem. I am aware of Dons advice about cold seizure and am fully committed to allowing the engine to warm and properly cool before take off and shut down. I’m not big on modifying beyond factory recommendation but the manual states on a factory piston that .003” is maximum wear before you have to bore. Machinist stated he would hone .002” beyond original spec before he would bore to next size.

Wiseco target bore (.030 over): 3.6565 = .006” piston to wall clearance.


machinist bored to: 3.6575 = .007” piston to wall clearance

[Savage]

Wiseco pistons were fine when I raced motocross, but I still would have used stock pistons in a Mercury Optimax due to the operating conditions and fuel mapping.

[Basshead35]

All other cylinders were within spec. The #6 cylinder was bored .030 over. The engine was overhauled by the factory book. New wiseco pistons in all cylinders. Block and rods cleaned thoroughly and inspected and replaced bearings, seal rings, gaskets and seals, all torque to yield bolts and torqued to factory spec. All Mercury oem parts. New fuel rails, new air injectors, cleaned and tested fuel injectors (compliments of Don at European Marine). Primed oil pump and verified all bleed passages were clear. All oil lines are hooked up properly with a little power tune added to the ends before installing and secured with zip ties. Inspected oil fittings and check valves (had to replace a couple out of precaution). Replaced thermostats, water pump, and inspected poppet valve. Engine does not overheat. Initial crank, I shut off immediately to clear the oil that races the motor on initial startup. On third start up the engine ran and idled fine. No performance issues. No warnings or codes displayed on Smartcraft gauges. Now has 2 hours of operation and break in mode has expired on the countdown on the smartcraft gauges. Continuing break in procedures per recommended time intervals.

Just a little background on what was done…

[RFSims]

An engine built with forged pistons needs to be set up a little looser than one with cast pistons, due to greater expansion of forged vs cast. When I rebuilt my old 90 Yamaha this is the reason I went back with cast. I did not trust MY ability to set the engine up right with Wisecos. If you mechanic is good and the motor is running fine I wouldn't worry about it.

[EuropeanAM]

While I wouldn't have recommended Wiseco, I won't say it's a problem in an of itself (used a lot of them in years gone by).

Boring and/or sizing doesn't involve just "punching for a target size from a sheet". It involves measuring the exact piston going in the hole.

What were the size, taper and out-of-round measurements on the other 5 bores?

Always use the measurement method specified by the piston manufacturer. When you go outside that recommendation, you are experimenting and must own the results (good bad or otherwise).

Before you go too deep into this... make sure it's not reeds or the air compressor you are hearing. Really a bit difficult to ascertain "piston clearance problems" in one particular cylinder (at least for me).

Easy way to determine if you're hearing the compressor: Flywheel cover OFF, start engine and idle. Momentarily put thumb over air inlet for compressor. Remove finger before engine stalls out.

Noise ceases: It's coming from the compressor.

[Savage]

According to his description the noise can't be coming from the compressor......

"Seems to go away after a good run or warm up. Will hear it sometimes and after warms it goes away. Barely give it throttle and no longer hear the tick"

[Basshead35]

While I wouldn't have recommended Wiseco, I won't say it's a problem in an of itself (used a lot of them in years gone by).

Boring and/or sizing doesn't involve just "punching for a target size from a sheet". It involves measuring the exact piston going in the hole.

What were the size, taper and out-of-round measurements on the other 5 bores?

Always use the measurement method specified by the piston manufacturer. When you go outside that recommendation, you are experimenting and must own the results (good bad or otherwise).

Before you go too deep into this... make sure it's not reeds or the air compressor you are hearing. Really a bit difficult to ascertain "piston clearance problems" in one particular cylinder (at least for me).

Easy way to determine if you're hearing the compressor: Flywheel cover OFF, start engine and idle. Momentarily put thumb over air inlet for compressor. Remove finger before engine stalls out.

Noise ceases: It's coming from the compressor.

i utilize electronic chassis ears. Put the head set on and it amplifies sound. Connect the alligator clamp of the device to a long screw driver and touch around on the block and that is why I say it is definately coming from number six Piston.

I don’t disagree with anything you say but I did speak about this with the machinist and Wiseco reps. Wiseco stated they put a coating on the piston for Pro XS (Armor Glide). They do not provide a piston to bore clearance. Only a target bore. The piston size by the blue print is measured before the armor glide coating is applied... the target bore minus the blueprint piston size is .006”. If you measure the piston with the coating you will not have the clearance with the target bore size on the spec sheet. Wiseco rep says hit target bore on spec sheet and install piston. Regardless the extra .001” will give around .006” if you measure piston with coating. . I went into long conversation about this with the machinist.

Machinist did not provide a spec sheet, but measured all cylinders and said all other 5 cylinders were within spec and had pistons in hand. Wiseco says hone Std. piston bore to .001” beyond factory size for nominal bore and install piston. I recently did an evinrude 225 and all went well with same machinist. I have built about 40 engines in the past 15 years automotive and some outboard. Pretty experienced just don’t specialize in optimax....

I know it is hard to give advice without physically seeing it in front of you or hands on with the build.

I want to to rule out anything else and you may be able to help.

Question 1: how do I know that the piston on #6 is getting oil. The bleed line going to that cylinder is not clogged but air blows to the cylinder while blowing through the check valve. And is blocked coming from the cylinder when sucking air from the check valve. The oil line goes from the check valve on the block on #6 and connects to the fitting on the block just before the adaptor plate and plenum per the manual. Is it possible oil is not flowing to the cylinder through the bleed line?

With the motor off, I tested the oil pump by priming it and ran the lines into a small bucket to ensure oil was flowing from the oil pump. checked all lines fittings and check valves to ensure they were clear. I then attached all lines per the manual and primed the oil pump to purge air out of the lines as per the manual. VST tank was full of fuel after pumping bulb. All worked well. once motor was started I cracked the screw on top of the engine mounted tank and it filled up with no issues. I believe the oil pump is feeding oil to the engine and is hooked up correctly.

Question 2: I replaced the crankshaft seal rings and the block did not have any grooves and the seal rings did not bind as per the manual. The seal rings are staggered 180 out front to back. Although I do not suspect this, would a seal ring cause a performance problem and or lean out the cylinder? Engine runs great...


going to stick a borescope in the cylinder to check out the cylinder. Not trying to over react. Going to get another run on it this weekend and go from there.

Thank you all for the replies!!

[fuelleak]

Id be interested what you see with the bore scope after a few more hours. If the skirt is banging on the sides of the cylinder Im sure you'll see the wear.

[Savage]

Exactly how did you prime the oil pump/system?

[Basshead35]

Exactly how did you prime the oil pump/system?

Primed the oil pump twice just to ensure the oil pump output was working. Engine not running I primed the oil pump with oil lines going into a small bucket to ensure pump was pumping oil. Then reinstalled all lines and oil pump then primed again to clear air from lines as per manual. VST tank was full of fuel as the fuel pump runs also during the prime procedure.

[Savage]

How did you activate the oil pump?

[Basshead35]

key switch and shift method. Break in mode.

[EuropeanAM]

Post#10:

Question #1: Oil is not fed through the bleed line. It is delivered directly to the REED PLATE, ingested through the reeds and crankcase. Bleed lines simply return un-used and puddled oil (with perhaps a small amount of fuel at times) to recirculate it.

Question #2: Doubtful, though all of the sealing rings should have been facing UP when you assembled the front half of the block to the back portion.

While it may sound unusual, next time you are running the engine check the items I mentioned in #8. Noises in these areas CAN be affected by temperature, believe it or not.

[Basshead35]

Post#10:

Question #1: Oil is not fed through the bleed line. It is delivered directly to the REED PLATE, ingested through the reeds and crankcase. Bleed lines simply return un-used and puddled oil (with perhaps a small amount of fuel at times) to recirculate it.

Question #2: Doubtful, though all of the sealing rings should have been facing UP when you assembled the front half of the block to the back portion.

While it may sound unusual, next time you are running the engine check the items I mentioned in #8. Noises in these areas CAN be affected by temperature, believe it or not.

Will do. Thank you.