Robbie Racer

I was wondering if anyone else out there is running a large bore size (4.625") blower motor (Merlin Pro tall deck block). I am having problems with early (20 hours) ring failure and would like to know if any one else has this problem. We refreshened the motor over the winter (because of excessive oil consumption last season) and had the block machined with piston oilers to try and pull more heat out of the pistons in order to get better ring life, but that didn't seem to help this problem. We put back in the same type of rings (Speed Pro, 1/16", 1/16", 3/16" oil rings and a Hell Fire top compression ring). It uses a 1/2 quart of oil every 1 hour of run time. Any thoughts if the cause of this problem is caused by excessive heat generation between the very thin cylinder walls? Or, should I be using a different type of ring?

Any thoughts are appreciated.

robyw1

Is this a siamese bore block? 1/2 quart for hour is a lot. How much boost are you running and what is your max rpm?

Roby

Strip Poker 388

iTrader: (6)

I would not think it would be a block . Whats your leak down .Maybe it your ring seal which would be the bore finish ,rings not sealing .depends on boost also . Give more facts!!Could be a guild but it would smoke I would think.

Comanche3Six

Are all the spark plugs oil fouled? What were the cylinders finished honed with? Did the machine shop use a torque plate to simulate stress of a cylinder head when the work was performed?

Lmarth

Robbie-- No expert here, but a few observations. What kind of pistons are you running? Anything special regarding ring placement,skirt length, rod length,etc.? Compression and leakdown as Strip suggested? Have you talked to the folks at JE Pistons? The fact that you're running such a big bore raises the question of what stroke you're running. More than 4.5"? The fact that you're using a lot of oil before/after rebuild suggests that something beyond the normal bore finnish kind of issues is in play here. The compression/leakdown numbers may indicate whether the pistons are rocking in the bores. It's conceivable that the top and even second rings are doing their job (good compression/leakdown) and it's an oil ring issue. My intuition says that with such a big bore/stroke, I'd get real friendly with the tech people at an outfit like JE. Just tryin' to help.--Lou

Robbie Racer

Thanks guys for the feedback. By the way the crank stroke is the same as the bore (4.625"). To answer some of your questions:
Roby: I think the Merlin Pro tall deck block is a siamese type block but not sure. I do know that there are no water passages between some (or maybe all) of the cylinders. I normally run 8-9 lbs. boost with 91 octane gas but occassionally bump it up to 14 lbs. boost on race gas. I have spun the motor to 6700 rpm but try to prop it to 6500 maximum most of the time.

Strip Poker: I plan to do a leak down this coming week but suspect it will be about the same as last year before we refreshed the motor since it's using the same amount of oil. The leak down numbers last year were: #1-18%, 2-14%, 3-8%, 4-32%, 5-24%, 6-16%, 7-16%, 8-24%. The only time that I notice any oil smoke is when I first start up the motor. But I do have a ugly residue on the back of the transom. I don't know how much of that is oil or because it may be running rich at an idle or mid range RPM.

Cigarette: The plugs don't look oil fouled to me but when we pulled the heads off last season you could see bad oil residue baked on top of a few pistons. I will try to find out from the motor builder what the finish hone was and report back here. The motor builder has a lot of experience with normally aspirated drag race type motors but not as much experience with blower motors. Do you think the cylinder hone would be different between these two types of motors? That brings up another possibility: I'm pretty sure he had the pistons gas ported. Is that a good idea on a long endurance type blower motor?

Lou: The pistons are by CP with a 8.25-1 static compression (and as stated above, gas ported). That's a good idea to talk to the piston people to get their take on this problem.

Thanks again guys.
Keith

articfriends

iTrader: (1)

keith,my motor only has a 4.500 bore but i'm using std deck block w/a 4.25 stroke so my pistons are kinda short and oil ring has a support rail (because they pass over wrist pin). I was concerned about blowby and oil consumption so i used std tension oil rings,plateau honed the block and used a total seal gapless ring and total seal quickseat powder to get a quick ring seat. I don't remember if the gapless ring was top ring or 2nd ring but i do remember that the rings were specifically for blower motor's and turbo motors. Total seal claims a leakdown rate of 2% or less, spot checking 2 cylinders on my motor last fall after 45 hrs on motor my leakdown rate was about 3%, i run 9psi boost (of course just like anyone else the motor doesn't see as much time under boost as idling thru no wake zones) but i am very happy with results and my motor uses virtually no oil and i get very little mist out of breathers(i change it every 25 hrs or so kendall gt50). Installing the rings and prepping the cylinders was a 8 hr ordeal but sure worth it in long run.You might want to try a similar setup, Roger hurst is my tech guy at competition products 1-920-233-2023 and the guy is a straight shooter-tells it like it is salesman and can sell you the same products at reasonable prices (if they make the rings for your bore size?). Give him a call and mention that smitty in michigan told you to call,good luck,Smitty. P.S.-what oil are you running and i'm sure you know better but your not putting sythetic oil in your motor before its broken in are you?

mcollinstn

I wouldn't have gas ported the ring grooves. Properly designed rings will pressure seat themselves without the porting. Porting might very well be overheating the rings.

Ring end gap. Make damn sure you're running enough end gap. Too tight of an end gap combined with blower temps can butt the ends and cause violently accelerated ring wear (or can lift off the top of the piston).

Proper bore finish, honed with torque plate for proper roundness, and straight bore. I've seen some nice motors get ruined by a taper in the bore - check yours from the bottom to the top of the bore for taper.

Proper seating of the rings. If you don't seat them, then they don't just do it by their lonesome. Whether you assemble dry with plateau honed "auto seat" finish, or seat them in the old fashioned way, there is still a bit of break in required before you trow the boost to it.

And on something that massive, I don't know that it would be a bad idea to use thicker rings (3/32") but I'd leave that call up to the piston men.

luck
\\

mc

Lmarth

Keith-- Thanks for the detailed response. Was that a typo or did you really have 24% to 32% leakdown last year? What was that all about? The drag racers on this site are very familiar with gas ported pistons, but I'll show my ignorance by saying that I've not heard of performance boaters doing it. Who knows what's in all out marine race motors. I would definitely follow up with Arcticfriends contact at CP. My money says you've got a piston/ring issue. Don't want to start a tinkling contest but there's been extensive coverage on this site that says you can run synthetics in a new motor with properly honed bores. A lot of car manufactureres do it with their performance models. If you want to play it safe, run conventional oil to start. My 800SC's use no oil. They were refreshened by Sterling 115 hours ago and shipped with Mobil 1 15w50. Keep us posted Keith as you wade through this.--Lou

Robbie Racer

Smitty, I wish I could get to only a 3% leak down on this motor. I also have a smaller 580" (4.50" stroke x 4.560" bore) blower motor built by another builder and it doesn't use a drop of oil either. Since it was built by a different builder, I'm sure a lot of things are different but I'm still wondering if the smaller amount of material between cylinders in the 4.625" bore motor is allowing a lot more heat transfer between cylinders which may be killing the rings. Thank you for your technical contact at CP info. I will ask my builder to talk to him to see if they can come to any conclusions. Last year I ran Mobil-1 15-50 but this year I switched to Synergen 15-50 because I get it free because of a drag boat race contingency awards program, I'm involved with. I might suspect the Synergen if I hadn't had the same problem with the Mobil-1. We broke the motor in on the dyno with regular mineral oil (pretty short session before we made a bunch of dyno pulls) then switched to synthetic before we made the pulls. I wonder if we had enough of a break in period.

MC, yeah I'm a little concerned about the gas ported pistons for this application. That will be one question that I will want asked of Roger at CP to get his take on that issue. I know that I got charged for a torque plate type of hone, so I assume that was done correctly.

Lou, no unfortunately that wasn't a typo. I really did have 24% and 32% leak in the two worst cylinders. My builder said the pistons showed a lot of heat had been in them so he recommended the piston coolers when he rebuilt it for this year to try and pull some heat away. He thought at that time, the piston heat due to sustained WOT runs was causing the ring failure. Now, it looks like something else is the cause.

Thanks again guys for the great feed back. I will keep you posted as to further developments.

Keith