Printable View
got myself ahold of a extra block. 91 or 92 omc 3 cyl. 56 cu split port block. wanting to do something extreme. Like to put 3.5 inch piston and stroke it. can it be done? How far can you stroke one? What kind of sleve would you put in it to make it last? and who would i need to get in touch with to construct a monstrosity?
thanks
river rat
For the effort and $$$ you'll need to fiddle with that 56 cube block you might find it easier to pick up an SST60 powerhead, it is 56 cubes, puts out around 90 plus HP and parts are still available from Sea-Way marine in Seattle.
what would be a better block then, a sst60 or to get a 90 hp yammi?
Not familiar with rice motors, if you have a tower with the 56 cube bolt pattern why not take advantage of the SST60, if you have to come up with a tower then there is no real advantage going OMC.
It seems to me that the motors already used to race would be the way to go for one good reason.. the wealth of 411 about them. Other motors may not have been as studied/tested leaving you on your own to figure out how.. then you risk a dud or a bomb for the $$Quote:
Originally Posted by river_ratj40
Find a 56 cu. in. short block that was used before the SST 60 engine was released for production. The orginal design for this motor used the "Permenent Mold" method for the block castings. The SST 60 uses the
the "Lost Foam" method for it's block castings.
If looking at each together, you will see a number of features that would be better for performance on the "Permenent Mold" version.
It would be to long of a disscussion to get into all of the advantages here, but the most important is the shape and finish of the transfer ports.
The Hot set up would be to put SST 60 sleeves in a "Perminent mold" early block.
I would also advise against using forged after market pistons, they require more skirt clearence and this engine runs best with tight clearences.
Just my opinion after racing this engine since 1989.
[Just my opinion after racing this engine since 1989.]
And quite competetively, I might add!! Hope your doing well Sam.
Joe Schweickert
Thanks Joe, we keep busy at it.
Doing ok.
Sam Lebanco: Two summers ago at a neighborhood garage sale I picked up a brand new NOS - OMC 49 inch 3 holer complete block from the factory along with the blown up fishing motor it was to replace where its block had kicked a rod through the side of the block for $200.00 bux. I bought it specifically for a Super E Modified engine. Talking to other people, reading the posts here and elsewhere leaves me confused as there are so many pros and cons from everyone to using the OMC pistons or aftermarket pistons like Wiseco. Reading your post just adds to wanting to do the right thing and I have no experience with these OMC 3 Holers. Will you advise as your experience base is profound?
Hi John,
Just like everything else, there is many ways to skin the cat. Also, their are some pretty smart guy's with a lot of experience writing on this forum about this engine. All I can do is give you an opinion based on my experience.
I have won a few races, but that does not make me smartter than those guy's.
Here's a few things to think about, the OMC pistons were not designed to go racing, but a whole lot of work went into them. Just ask guys like Jim Nerstrom.
What I have found is that all the stock pistons go out of round after runinng them, which is the common complaint, that does not mean at running temp they are that way (can't measure them then.) I do know that some years, they were worse than others, but that was when they were measured out of the motor.
I do believe the ones we have been getting in the last 2 years measure better after running, but I don't know if that really means anything in the motor.
There seems to be a lot of misconception about forged parts by people that they are always stronger than castings. In very general terms this can be true because of the post forging grain structure and all that stuff they talk about, but there is a quite a bit more to it than grain structure.
I am not saying forged after market pistons are not good by any means, but I would like to see "real" evidence that in this motor they are any better.
(maybe I've been a engineer to long)
I do know because of the difference in the physical properties of the cast and forged materials, you need to run more clearence with the forged ones.
I also know that these motors run best when tight and after .0045-.0050 skirt clearance they don't win races, they still turn up good till about
.006-007, they just don't come out of a corner the way you need them too in a real race.
Do the forged pistons fit just as good under dynamic conditions running in the motor, maybe, they don't do a bad job thats for sure.
Just show me the dyno sheet . The cast ones have done pretty good for us under racing conditions.
Sam LeBanco:
Thank you for your insight. The only reason I will disassemble and re-assemble this factory replacement block is to deal with porting work for other anomolys that may not mean anything to a stock engine but to racing one does and re-assemble it with its new OMC pistons. For the Future I will sure watch for the wear limits you are describing to later act on. Why spend a whole extra wack of extra money for other aftermarket pistons where you have a new set to count on from the original purchase price to work with first time around at least.
Any advice on breaking the rings in while on petroleum based oils and when switched over to synthetic and advise what synthetic is best for these 3 Holers overall.
Again thanks. :)
John
Everyones got there own ideas about break in also as you know, I've tried many ways but went back to a much slower and longer period than I've used in the past.
The reason for the switch was my research on a common problem with these engines; microwelding. Which as you probably know is the transfer of aluminum from the ring groves to the the bottom side of the rings, (mostly the upper one). When this happens they do not seal well.
This engines rings have a very large cross section which makes them very heavy (great rings for fishing and sking). To heavy for the RPM range we use them in. If you have a copy of Gorden Jennings book "the 2-stroke tunners handbook" he explains in great detail the subject.
Using the equations he presents to help predict the problem of "ring flutter"
you will find that these rings are in danger of flutter as they get over 7800
RPM.
We have always known this, and figured that was why we generaly find evidence of the problem during rebuilds somtimes, as we are turning a bit higher.
After seeing more microwelding than usual, during last years tear downs I decided to research this subject. There is to much information to type, but lets just say all modern 2&4 stroke engines have coated rings. Most of the coatings are propritery and I could not find a source to do mine.
There's a lot of coatings out there but not these.
After not finding a source I was frustrated and called and old engineer friend
I worked with at OMC, Dave Haman (we did the design work on the 45ss engines midsection and gear cases, also the OMC "A" motor.)
By the way he is currently the manager of Bombardier's (OMC's old) test station in Florida, between that and all his time in engineering in Waukagen,
he's a pretty smart 2-stroke guy. As we discussed the problem, he filled me in on something unknown to me, that being, microwelding most happens during a tough brake-in,... then just gets worse.
Well, now I break the engines in like my old stock outboard days, nice and slow.
As far as oil goes, man, what a can of worms no matter what I would say, there are a million other idea's out there, so I will tell you what we have used in this engine with good results, Bombardier, Yamaha R and Xamax.
I have alot to learn.
Sam LeBanco:
My aircraft pilot neighbour who go me involved in all this in the mid 1960s when doing his rebuilds on his C-Racing, C-Service and then his racing KG9 Merc would spray all his rings with some kind of graphite spray on each side that would dry and harden before he would flip them to do the other sides for installation. This he claimed would help with a slowing of the break in of those real wide rings he used. He also used some kind of graphite additive in his fuel mixes as well that left a grey residue streaming down outside his exhaust ports. He never talked about things such as ring flutter and if he did I was too young to understand that, he kept me to basics as a protege. One thing he did mention was wanting some kinds of rings that fitted ring groves as standard but tapered outward to half the ring grove width at the cylinder wall as being a better racing ring. That was still greek to me too! I never saw rings like that until the later 1990s for Mercs running Turner pistons. Just last year I made up a D-Mod gas engine with NOS Turner ultralight 2 ring gasser pistons where I installed these type of NOS tapered to the outside half width rings that looked they were a kind of chrome high tension ring material. I have yet to test the engine. I take it that narrower rings of suitable material took out ring flutter at these higher rpms? I suppose that these modern day teflon and ceramic coatings and sprays also help prevent ring problems at high rpms?
Its entirely new to me about metal transfers from one side of the rings groves to another. I saw some weird stuff on the Turner piston ring groves on scortched, scored, melted and fried pistons from Alky deflector engines but never on the stock or mod Mercs I have worked on. Is that what you mean by metal transferance? I would not have recognized what I was seeing other than thinking that the piston maker made things that way?
There is so much to think about in your post I have to go into Jennings material to get further out of what your saying. For anyone else to read I do believe there is a thread on BRF with links to download his, Jenning's book.
Thanks for the break in proceedure advice, slower means better or even more long lasting parts wise hopefully. I notice you did not mention Red Line synthetic 2 stroke oil for gasoline fuels. With sitting on about 6 gallons of it, I must ask if it has fallen out of favor these days??
A few years ago I had the misfortune about not knowing anything about Amsoil and that Amsoil synthetic was just that being synthetic and could not figure out why the Merc 55H just would not break in its rings no matter what I did. When I found out the whole experience soured on me thinking it was a weird engine of no use and there it was the synthetic oil screwing up the rings breaking in all along. What a horrible lesson to learn about not knowing oil brands and using them thinking in that case thinking Amsoil was petroleum based with no can or specs to read and find out any different at the time.
I am defintely going to use the new OMC pistons already loaded into the replacement complete block and be mindful of all your pointers.
Thanks for all that info. :)
John, sure wish I could get some of that stuff your friend used on his rings.
Actually there is some stuff like that avaiable from Dow Cornning and a few other places, that guy was pretty smart. I would not use it in the fuel though.
Not all engines suffer from Micro wellding, I never saw it on any of my stock or modified engines.
The best way to describe microwelding is, you will know it's happenning when you find small pin head or smaller size deposits you can feel on the bottom side of the rings, when you clean the ring up, the spots will be the same color as aluminum (because it is). You will see the associated pock marks on the ring glands. To much heat.
I have never run red line, but my best friend builds many many kart engines
at his shop, and they use it when they can't get the Xamax I listed.
The rings in the sst60 motor (56 cuber) run pretty hot, but not as warm in the 49 cuber. The 49 cubic "sport E motor was a way way better engine, with a much more robust block and quite a bit more water jacketing.(great motor)
When testing projects while I was at OMC, from time to time Jimbo would also be out testing at our test station that was in fox lake Ill. so of course we would stop to watch. Once while testing his Mod 50 motor, I heard Jim Nerstrom tell Jimbo to keep the motor under 9000, I'm sure he didn't always do that though. I think the mod 50 rings were similar but not sure.
I don't think they had problems with microwelding but that block had a lot more cooling then out "60" motor also.
Sam LeBanco:
The graphite spray that Ted Coates used on the piston rings was different and he got it from mechanics at his commercial airport repair depot. The small can of graphite lube mix that was sold for fuel mixes specifically and different from the rings sprays was from "Wynnes" products, who also made a lot of other specialty lubricants to general sale to the public as well. He told me it was good for the OMC bushings still in the engine as well. He was also in the midst of converting his engines to more modern bearings and seals. After conversion he kept on using the Wynnes graphite lube in his fuel.
I thought the sparkplugs would foul on graphite being what it is but he always changed sparkplugs on the Elto and Johnson every heat anyway with clean ones so he never saw a problem by using his practices of changing plugs religiously to get excellent starting and running. For some reason he only changed sparkplugs on the Merc KG9 (Champion J4J) on the next race date but not at any other times between heats or even on a 2 day race weekend. He had no problems there either.
I was under the impression that the OMC 3 Holers being loop charged that they would run inherently cooler than their older deflector engines by virtue of the new technology but I am being informed that in either case that is just not so, be it a 35HP deflector or a 3 Holer looper. That for a ski/fishing based market that they are oversquare engines with way larger piston bores than crankshaft stroke making them high revers by their nature. Is there no way to make them transfer heat faster and tuned to run cooler? When it came to Merc/Mariner 3 Holer direct charged engines I thought my burn them to bits days were over and OMC a lot lot better?
People I know that are working on OMC 35 - 2 cylinder class C Modifieds are going to be very interested in your posts as there are 3 versions ports wise of these deflectors being constructed during their same years of production that from examining their innards as they put it have "racing written all over them"! They seriously want to boot some Yamato butt and are concerned about anything that can be done to make these engines heat managed, powerful and reliable given engines spec'd limitations for the class?
The nice thing about all the OMCs of yesteryear is that they are so so plentiful and so inexpensive to buy used albiet that they are all so heavy mainly from flywheel weight. Do these OMCs have to have such heavy flywheel systems to keep the whole motor stable or can they be made way smaller and lighter and still keep stock ignition parts going?
Sounds like asking for a lot of advice, yes but there are a lot out there who want to race and see racing spread through economies of scale, so OMC it is and just like Mercs here everything from the similar eras are so inexpensive for our sports use.
Looks like people are hard anodizing the piston crown and ring grooves to get over the microwelding problems these days
One question is how fast are the C-mods now? There's no question about power out of a corner. Ive been modifying 25/35OMC's for fun which also means no rules except they have to be closed exhaust to run locally. The flywheel is heavy, why is probably the go slow aspect of motoring that they are good at. The steel starter ring can be easily removed but its not recommended to cut down the aluminum. The inner dia is relatively small so a custom or retrofitted wheel is possible ?. Also the balance work on these is probably not meant for more than the 5000-5500 R's intended. The piston assembly weights are likely to not match up very well either. There are a good number of different versions of the cross flow twin or parts contained, while mostly looking the same externally. I'm not near enough to where they are being raced [not allowed in the APBA]. I do think there is potential to be competitive with the 302's or MK30H mods in time as more experts take interest.Quote:
Originally Posted by John (Taylor) Gabrowski
Lemme see, the SST60 is 56 cubic inches, the Yamaha 90 is 70 cubic inches. Which one looks like a better candidate?Quote:
Originally Posted by river_ratj40
Tim
Hey John,Quote:
Originally Posted by John (Taylor) Gabrowski
Just finished with my 666 and have time to answer. Be wary of NOS cast 49.9 pistons they are known to fatigue, crack, and blow chunks. When you disassemble your perforated powerhead you'll more than likely find the rod and crank perfectly intact, and the window caused by piston chunks getting trapped between the rod and crankcase (sometimes block). I've seen dozens like this, and most are easily repaired by heliarc and a little grinding. Though casual observers think the rod has thrown, but I've never seen a broken OMC triple rod unless run without oil (got one in stock), and have never, ever seen a broken crank.
If you purchase late production cast pistons and judiciously deburr and smooth, they will last years in a fishing engine. If you intend to race the engine, be sure to dye penetrant check cast pistons before they go in and NEVER install used cast pistons unless you know their history. I've used both OEM and Wiseco forged aftermarket pistons in racing triples with good results. In these cases, we change them every three seasons regardless.
Sam's advice is superb given his SST60 racing experience, in particular the ring flutter, micro-welding as pertains to breakin. The one item I don't recall being talked about is proper engine warmup. Most racers start a stone cold engine at full throttle to get on plane immediately to mill the course. Short of flying immersion, I'm convinced this is the single most damaging event a race motor experiences. Consider that cast pistons expand less and run tighter clearances than forged (as Sam pointed out), so they are less prone to cold start damage. Forged pistons do expand more and don't take well to WOT starts. They need be warmed gently - actually it's best to warm any engine gently - before stabbing the throttle.
Just my two bits,,,,,,,
Tim
Tim:
Your comment about letting the engine get to operating temp before "stabbing it" is well taken, and I remember a problem I had with a "D" (40 CUI) Konig in the early 70's. At the time the only piston alternative to the Konig piston by Mahle, were cast pistons made by Stan Leavendusky Sr. Stan of course had much experience casting pistons for the Quincy Flatheads of the time, and for quite some time right up to the end of their competitiveness against the Konig, was the supplier of pistons to Quincy in both replacement and OEM categories.
I had purchased a D Konig that was in bad shape insofar as the bores were concerned, and asked Stan to bore and fit a set of pistons to it. Long story short, I kept sticking one or more pistons as soon as I would open the throttle of the motor after starting and running a lap or so at part throttle, as I was always a believer in taking it easy for a little bit until everything had had a chance to warm up some.
This happened about 4 or 5 times with these pistons, and finally, as I could not afford a couple of pistons everytime I ran the engine, I sent it to Harry ZAK who had started to work on my engines, first with his pipes and cut rotary valve disks. Harry looked at the way the pistons were sticking, just barely a small smear right by the exhaust port and just above and a half inch or so below the ring, and only enough to kill the motor, and then the motor would be free by the time the boat coasted to a stop.
Long story short, he called it a "COLD STICK" and said it was happening because the aluminum used in the piston did not have the same coefficient of expansion as the Konig/Mahle pistons. He (Harry) fitted new pistons (4 Mahle's) and I never had the problem again. Not to say that Stans pistons were bad, but just not the right mix of aluminum evidently for that engine. We also tried various clearances and were not able to stop it from sticking by that method either.
Harry later made some small thermostat housings from billet aluminum and used OMC thermostats for various racers that ran both Konig and Yamato engines, and that seemed to help the sticking problem and also the motor ran much better from the word go, as it would usually take several laps in a race for one to really come on, leading him to believe that the motor was not fully at operating temp until it had been run hard for several laps. In the PRO category, since we only ran 4 laps, and usually took it easy for engine longevity while milling for the start, the engines never really got warmed up till run hard for a lap or so.
The one bad problem with the thermostat housing was that that is was just another place for water stoppages to occur due to picking up trash while running with the force-feed water type pickup, and you really needed a "telltale" so as to be sure you were getting plenty of water while running.
Woof! Your frustration with the Leavendusky pistons must have been maddening (I've have been there). It's difficult to race knowing the engine is brittle: You've always got the fear of an impending teardown and repair bill in the back of your mind. It's good you found Zak to solve the problem and put you in a position to focus on racing.
Knowledge of eutectic properties, mechanical engineering, and well instrumented dyno testing are needed to establish a durable engine. This is best done by an OEM or large aftermarket company, it's way too much for the typical racer. We can't afford the time or $$$ to develop durable parts, and the cost of failure is high.
Regarding piston/bore fit, it never ceases to amaze me how many people mis-direct a machinist. Example: When a piston comes marked +.030", this means it is designed for a bore .030" over standard: Clearences are always machined into the piston. Several times in my career, customers insisted the clearance should be added to the overbore! Once I complied to find the engine would not support sufficient compression to run! From then on, if the client didn't agree with correct fitment, they were sent away to inflict the damage somewhere else.
Tim
Hi Tim
Can you do that with forged pistons as well?
Please restate the question more fully - I don't understand what you're asking.Quote:
Originally Posted by Powerabout
Tim
Do you run the forged pistons in std + 030 bores?Quote:
Originally Posted by Tim Kurcz
OMC never had forged pistons so hence where was all the testing done re piston to bore clearance?
thanks
You betcha. I've installed Wiseco forged pistons in standard, +.020", +.030", and +.040" bores. Wiseco provides the product and dyno testing. See http://www.wiseco.com/AboutUs.aspxQuote:
Originally Posted by Powerabout
3115PS $100.00 3.000in STD Cylinders: 3
Notes: Loop Charge
3115P2 $100.00 3.020in .020in Cylinders: 3
Notes: Loop Charge
3115P3 $100.00 3.030in .030in Cylinders: 3
Notes: Loop Charge
3115P4 $100.00 3.040in .040in Cylinders: 3
Notes: Loop Charge
Except for running without oil, cooling water, or too lean, they run just fine. There are some that say tin plated OEM cast pistons are faster, but I've no AB testing to prove this one way or another.
Please remember that all factory and aftermarket piston testing is done in service engines. The mods built in my shop see much more taxing duty. No manufacturer guarantees pistons in racing applications. I can tell you that both cast and forged will burn down if too much spark, too lean, too low octane, etc.
You know the saying: Too lean, too long, too bad!
Tim