Hi all.
I am in the process of tuning a ST V60 to install in an ARF SV11. The engine performs a hemi head and ABC P/L from Brian Gardner.
I broke it in recently with a 0.176" venturi, and the running was very sweet but weak, performing aprox 7000 rpm with the same 13x6 prop that my K model V60 performs 8000 rpm. I assume the cause is a drop in the efective compression ratio because of the hemi head, being in the process of trying with larger venturis....
If some of you have experience with hemis ST60, could you share your setup to use as a starting point for the fine tunning?

Thanks very much and kind regards from Spain.

Manuel.

Manuel,

Wow.  136 views and no replies.  Sounds like low compression.  Could be the head, but have you checked the piston to head clearance?  Maybe compress some by pulling a gasket, lowering the liner?  Some ideas.

   I think most people are reserving comment, me in particular since I have never run the ST60 in any serious way. But, this sequence of events does seem pretty familiar. One of the few things I do know about it is that, unlike most engines useful for stunt, you *can* get too little head clearance (as indicated by kicking back,  unexpectedly flaming out, etc). I am not sure that this is just a matter of the raw compression, it may be just the clearance. I know the same thing happens to the ST46, and even .003 additional clearance will usually cure it.

     Like most things, there was a huge overreaction to it, and I have seen many ST60s with so little compression ratio that the are no stronger than a good ST46s. The most egregious example was from a (justifiably) famous stunt flier who set up an ST60 with so little compression that he also had to include a MASSIVE venturi, which was so large, it came close to quitting on release when the acceleration caused fuel starvation. This was in a kit-sized Shark 45, you would expect an ST60 to yank that around pretty good, but it was hopeless, squeaky lean at the slightest touch of the controls, but absolutely no power. I looked, and it appeared to have something like 1/16" extra head gaskets, and turning it over, it felt like the glow plug had fallen out.

  I very strongly discourage anyone from "dropping the liner", its a questionable practice on a 40FSR, you sure don't have a timing problem with the ST60. Removing head gaskets is a potential solution, but I suspect that the modified head has already reduced the compression to the point that you cannot approach the stock value before the piston starts hitting.

   The solution in the example case was to run more nitro. The owner was running 5% on recommendation of the engine maker, I talked him into 15%, which markedly improved it and got reasonable power. I was trying to talk the owner into running YS20/20, but for whatever reason he chose not to, and I was looking around for someone with 30% or who was carrying around some pure nitromethane to mix with.

  So, the easiest and most obvious solution to lack of power due to low compression ratio is add nitro, keep upping it until something bad happens. Unlike a Fox (which also greatly benefits) you aren't going to break the engine, it will just start kicking back. But I have run as much as 30% nitro in a bone-stock ST46, including stock compression and head, with absolutely no problems aside from running out of gas right after the triangles, and tremendous power gain.

     Brett

 

 I see Brett and I posted at same time.
  Maybe Randy will see the post and have a comment.
Ed

Hi mates, thanks very much for your time and saring info. I will test lowering the head, and then increasing nitro to check the results.

Kind regards from Spain.

Manuel.

  I have built up a ST.60 with a Garner P&L set but have not run it yet. Brian usually includes the rod and wrist pin in his sets so the fit of those should be spot on. In his instructions, he cautions you to check the fit of the rod on the crank pin, and if it is tight, polish the rod until it fits.  When he builds P&L sets, he takes a personal survey of as many engines as he can to get the specifications he needs to produce them and comes up with an average that may be on the small side.. Sometimes that means a liner will drop right into a case, and some times not and need some polishing on the outside of the liner, or the big end of the rod needs to be fitted. I've built up OS.LA.46's, Fox .35s, ST G-51's and ST.60s from his parts with absolutely no issues and everything went exactly as he spells out in his instructions. Some parts needed fitting, and some didn't but the fitting was very minimal. On some engines, like the LA.46 , he produces a head for it because he has to make the top of the liner a bit thicker, and you have to use his head to keep the compression correct. He sometimes has separate hemi heads available for a reasonable price if you care to try those. With out seeing the engine, and from my limited experience with ST.60's, it's possible you might not have the correct head. The heads are not interchangeable between all models. If you have a stock head, I would try that, and also investigate exactly which head yours takes. I would not change anything on Brian's parts what so ever. If you have a problem I'm bet it lies elsewhere. You might not have the correct cranks shaft, for instance, as I think there are three different ones. And Brian bases all his ST. sets on versions of the engines with muffler lugs, as there is a difference in them there, so that is a possibility. I'll reiterate that I  find the quality of Brian Garnder's parts as good as you will see anywhere.
   Type at you later,
   Dan McEntee

I was an onlooker to the ST .60bb/Shark 45 fiasco that Brett mentioned, and later found out more on it from the owner. The whole story was that the engine was bought used, and the original owner thought the best way to ship the head shims he had was to install them in the engine so they wouldn't get wrinkled. I expect that the screws were not torqued much, if at all, which would make it even worse. Possibly, Manuel's problem is the same sort of deal? Or maybe Manuel is trying to run zero nitro? Engines gotta pump, and they are happier with more fuel, rather than less, IMO.

Personally, have only flown a real ST .60bb a few flights, but I recall asking John Leidle what prop I should start with, and he said "any 12-6", and did just that. Last time I saw John, I think was in Salem, and he was flying a ST .60bb with a 12-7 Master Airscrew wood prop...which I wouldn't use to stir paint without a fair amount of hand sanding and such.

Anyway, after a few flights on the ST .60 (it was Scott Riese's, and I was not yet doing the pattern...Scott's prop also, I think). Not wanting to damage Scott's stuff, I plugged in my Double Star .60bb, which is a clone with better QC. This one is an early example, and IIRC is an ABC, but maybe AAC (no rings). I like it a lot, and it likes an APC 12.5 x 6 quite well on 10% nitro (Powermaster 10-22, in those days was really 7%, or so I've read).    Steve

Yes, compression ratio is clearly defined as one volume vs. another.  And I realize some folks find it easy to measure.  However, for a given head shape, piston to head clearance is a useful measurement from some perspectives.

If you are installing new parts in an engine, whether they are aftermarket or OEM replacement parts; you should never assemble it without checking for correct fits of parts and definitely check the head clearance. Every machined part has a tolerance with the crankcase itself having the most possible variations due to the number of machining operations it undergoes. Even in high dollar high performance engines clearances vary enough to warrant checking. Head clearance is one of the factors that can greatly influence how an engine runs and should be set to a known value at least as a starting point. If you don't know how to check the head clearance, or deck height as some call it, you shouldn't be working on your own engine. I'm sure Brian sent some instructions for assembly and a couple shims. If he didn't specify squish band to piston clearance, ask him or someone who's running one where to start. Generally, a 60 size engine set up for stunt would want .020 to .030. Both volume and plug height above piston matter.

duplicate, somehow...

The Hemi head does have lower compression - but is intended for nitro use above 10%. It only came about because "some" people found them a bit difficult to tune with the stock head - but I suspect this was more because they were using the original head shim that had squashed down.

The same applies to the 46 and 51. They both work with the stock head and low nitro, but can be difficult to get right if running higher nitro contents. I used to routinely run 20% nitro in the 46 and as high as 30% at one point.

Manuel is running 7% nitro - so the stock head should be ok. If continuing to run the hemi head I'd suggest more nitro or a bigger venturi.

There is also the possibility it is a bit tight still and power will improve with more run time.

Yep

   That was also *exactly* what we found with the 46. You could run all the nitro you wanted but if that head gasket had visibly compressed, you were headed for problems - usually, it misfire in the extreme or just flame out for no apparent reason. I am not sure it was a matter of compression or head volume, just that the very wide "squish band" had so little clearance, stock, that you couldn't tolerate even .003-.005 closer.

     Brett

 

Hi all.
Update March 21st.
After some trials this weekend, basically testing lowering the head, and later increase slightly the venturi section, and as was predicted, the power is near to the stock unit with the squish band head.
Accidentally, as the tests are being made without muffler, I discovered than the Gardner ABC piston performs a little sub piston induction, althought any of my stock units or my George Aldrich ABC doesn´t have. The unit is built int a stock ST60 K model case, so no modification can affect to the relative position of the piston, as the con rod is sipplied with the PS assy.
Will check soon the performance with muffler, to see if the SPI affects the running quality.

Kind regards.

Manuel.

Manuel,
Robert Storick runs a number of Brian Gardner ST V60's and speaks very highly of them.

If you have technical questions I would ask Brian himself. I have always found him very approachable and even answers my stupid novice questions nicely.

If you would like his email send me a PM.

Craig

Woud be helpful if some has a ST60 with the Gardner PL assy or remember having built or run one (I think Randy has biult some of them for customers ) carify if the sub piston induction detected is normal or not.

Thanks again mates.

  I have built up one ST.60 with Brian P&L set but have not run it. I do not remember if I saw any SPI, but will check. If you have pieced together the engine from parts, that may explain it some. I think there are 3 different crank shafts during the run of the ST.60 I think the rods might be the same in all of them. I am not familiar with the lettering system you mention but in Brian's instructions he calls out the the sets are designed to work in the cases with muffler lugs. I'll be watching this thread to see what Brian has to say.
   Type at you later,
   Dan McEntee

 .176 spounfds like a rather small intake . i recently saw some .185 in the 60 , & thought small - ST 46 size ! .

Spraybar 4 mm through , & .312 isnt unusual , thats vaugely .212 in a std. set up . plus or minus .

Thanks very much Randy, I´ll test with the stock K head.

Kind regards from Spain.

Manuel.