Causes of tight wrist pins and scuffed pistons ?
 

Engines were HAWK 525's
35 hrs all using 93 octane pump gas
5100 max rpm, never held there for more than 60 seconds at a time mostly cruised at 3900 rpm
454's .030 over (going to measure exact bore tomorrow)
TRW 2399 pistons
088 heads 119cc chambers
28* timing ngk r5674-7 plugs
had b&m 174 blowers with 800 cfm holley's
comp 280 ah 114 cams .547 lift 280/288 114 lsa
rod and main bearings look fine, couple marks/ lines but not beaten out or uneven wear

7 out of 8 pistons in each engine had tight wrist pins, a couple galled the piston when pressed apart.
3 scuffed pistons in one motor, 2 in the other.
Machine shop says detonation but the plugs look perfect, no signs on the domes of the pistons and the upper bearing halves are mint.
I believe they were assembled at .004 piston to wall but will measure to verify, and are going back together @.0065

Any ideas what caused this ? was it detonation ?
I don't run thermostats in the intakes water temp is usually around 135-140 and I never run it hard right away always idle for 5 minutes or so away from the ramp.
They have hp500 oil coolers and thr=ermostatic oil filter heads.

Any help or input is greatly appreciated.

dome pic

im thinking detonation because the wrist pins are tight,the piston pin bores are probibally egg shaped/out of round .i believe the pistons are forged,and .004 piston to wall is a little to tight,espically on a blown deal,but the plug in the pic looks good.what is the compression ratio,and how much boost at wot?also,who did the assembly.

8.8-8.9:1 compression ratio standard fel pro marine head gaskets 5 lbs wot, 140* water temps, I bought the motors out of my buddies boat with less than 10 hours on them. He had all the receipts etc. Have to check who did the assembly.
8.84 according to jeg's

28 deg timing puts a lot of heat on the piston top,is there any scuffing inbetween the ringlands?

what side og the pistons have the scuffing? inside or towards the outside the block..

Outside iirc

No scuffing visible on the ring lands

Tight wrist pins would cause the skirt to skuff, piston could not rock freely and would cause side load on them. If you had deonation to the point of knocking a wrist pin hole out of round the upper rod bearing would show copper. Post pics of the rod bearings. sound like poor machine work, and bad assymbly. Side clearance sounds a little tight for a boosted motor, but the piston manufactuer would have the determaining specs for their product.

James...did you check the ring gaps? That's the only thing you haven't covered....you looked at every thing else. I have seen this before...the motor I saw that was like this was set up too tight on the clearances ( Rod and Main Bearing along with ring gap) and what I remember looked like your pics.

it is posible that the assembler did not oil the cyl walls or piston skirts,and the piston pins,the damage would have hapened right away.what prompted you to take them apart,loss of power and oil use?

One was making a noise, decided to double key the cranks, and machine shop insisted on detonation, they also said .004 was fine so I said well both motors are tuned and run the same way lets see what the not noisy one looks like

28 degrees is a baseline starting point depending on many variables , i would say that 30 to 32 degrees is where you'll end up, but be cautious as the pistons you're using aren't "my" first choice lol
True blower pistons are designed to withstand the higher temps associated with blower engines, I'll call you and we can discuss this in greater detail...

Adding 420 blowers with chillers, reason for double keyway on cranks

How are the exhaust valves? 28* coupled with a lean afr, baby blowers=tons of heat in the cylinder.

and the pistons are not for a supercharged engine,all that heat may have caused too much piston expansion,once the piston started scraping the cylinder wall and scuffed the skirts the drag coupled with the heat oblonged the piston pin holes.

i remember when hawk was building those .they started out with a base 420 merc i belived they changed the cam and bolted on the b&m blower .they had a lot of problems ,dentonation!!! i have a question did the motor set for a long time? any heat signs of heat on the bottom of piston under the dome?

fixx
 

reason for asking,i had a customer that scuffed all the outside's of his pistons..he sucked up sand and all the sediment would not allow the water flow properly and the cylinder wall expanded and did the same thing your did..sea strainers cured his problem after a bore and a set of pistons..

Thanks fix, I have monster strainers, and there is no sediment I can find in the block.
I think mike and joe may be on to something.
I think the pistons were just too tight for the application. I know the pistons aren't designed specifically for a blower, and I don't want to put a bunch of $$ into these 454's right now. I plan on building a pair of 540's in a year or 2, so to put $1500 worth of pistons in these to only use for a short time just doesn't make a lot of sense. ESP when I have 2 sets of these pistons for short money. I'll get the bores measured up and see where they are at.

The hawk decal on the blower said 26* max but these were originally built in the early days of supercharging pleasure boats.
The bottom of the domes look fine, no excessive heat in the tops of the pistons.
I know I sound like a cheap a$$ but just got married in may and I'm buying another house now, had to pay off both trucks, and any cc's to get approved. Money is tight right now. I sold my old blowers and bravo crap and that equalled enough to buy the 420's.
Do you guys think these will live if I open the bores to .0065? Guys are putting decent size whipples on otherwise stock 500efi's and doing ok right?

Thanks dean, Artie and Gerry always speak very highly of you. I'll give you a call tomorrow.

looks like a oiling issue to me...with pistons all scuffed and bearing look like hell...top of pistons and plugs look good...what oil pump, oil , cooler, oil lines ??

What bearings do you see that look like hell? First layer isn't worn or scuffed on any. Only thing I see is a couple very small score lines from aluminum that scuffed off the pistons
Hp500 oil cooler and thermostatic filter head, stock merc hp500 oil lines, high end melling coated and blueprinted oil pump.

Dean is the man!

That's what I hear!

Your running high compression piston in a blower motor on pump gas.....

So what are you saying happened?
I was under the assumption 8.8:1 wasn't high.

Not exactly. With those pistons in a 460 inch motor, he's under 9:1. Depending on the deck height, chamber size, and gasket thickness, 8.75:1 is probably where he is.

Nothing wrong with running that as long as the boost is kept within reason. About a million guys have slapped roots, whipples, or prochargers on stock merc engines with good results over the years. Running the same pistons, heads, etc.

I think he had a couple things against him.

#1 questionable machine work

#2 174 Blowers. They belong on a small block. They do nothing but make heat on a 454 after about 3lbs of boost.

#3 28* of timing. Too little of ignition lead is just a band aid to try to make the engine survive with the heat pump blower up top.

If he goes with a rebuild, the machine work done correctly, all tolerances in spec, the big 420 blower underdriven and around 5lbs of boost, right fuel setup, 32* or so, he'll do just fine. The big blower, dual carbs, added timing, is just flat out gonna run so much cooler.

God I hope so lol
Side note mr.fixxall, mild thunder, adk61, mike tkach, dean, etc thank you all for your experienced and helpful input.

What is the quench distance? Are you at zero deck? negative deck? Makes a big difference when your putting timing in a motor. Also, piston to wall is a little tight but doesnt look like that was your issue. Detonation will open up the ring lands and you will loose your lubrication on the pistons. It will also take the molly right off the top ring as soon as it detonates. should run a tooled steel top ring in a boosted motor it's worth the extra money. I've put timing in boosted motors without any issue but I've always payed attention to the quench area. Guys that are slamming motors out the door usually don't do this cause it takes extra time...

Not sure on the quench I'll have to check upon reassembly, the rings and ring lands look fine.
Maybe I just don't want to believe it, but I've run a lot of big power motors, granted not many in boats, but there are no signs of detonation anywhere on these. I've detonated pistons into a million pieces, and I've made some last that should have blown up right away. How could it have beat the wrist pin bore out of the piston without a single sign on the plugs, bearings or domes??

the pics of the bearings don't look good to me...now might just be them on my end...also, not sure if merc does anything diff on a HP500 oil lines, but std 502 stuff is junk, search here couple or great articles, but line ends, fittings etc are terrible, are you running a oil temp gauge ??? need to with a blower set-up, also did you have any carb flooding/super rich ?? does not take much fuel in the oil to cause issues like these...I can tell you that from experience on a small blower engine I killed a few years ago....

I'll search about the oil lines, but in person the bearings look fine, except for a couple score lines like I said.

seems like the quench issue is taking OSO by storm.. lol what's your opinion on this? where do you run a boosted engine?

opinions are like a$$holes... everyone has one!!!:eekdrop:

Mine is set at .050".
I keep .010" on block deck for future deck squaring and use .040" head gasket.

And they all stink:lolhit:

yeahvole!! lmao :whistle:

mfg specs are a recommended minimum, a boosted marine engine is often much greater, not uncommon to see .008 piston to wall on a 4.500 bore a tad less on a 4.250 must remember that controlling the expansion rate of a block at 140 degrees is nearly impossible, so err on the side of caution and add some clearance IMPO