Over the years I have seen adds saying a Bellanca or Stinson was for sale with a heavy case 150 Franklin. I always assumed they were putting a little hype into their add or were confusing the information on the 165 Franklin which had a well documented light case (with problems) and later 165s with the improved(heavy) case. I have a stack of Franklin books almost a foot high, and I have never seen even the slightest reference to a heavy case 150. Over the weekend I found out I was wrong. In looking through parts at a friends hanger, he pulled out a case that had been in a box for years. My friend looked at the casting numbers on the side of the case and said it was a heavy case 165. He then looked at the data plate and it was for a 150. The engine number stamped on the plate ,and the number stamped on the boss on the case side were in the 150 number range. Now that we were really confused we measured the lifter holes, and they were the 150 size (165 lifters are a little bigger). It also was drilled for the oil control prop and had the shelf in the case ( a 165 feature) that prevents a loose cylinder liner from dropping down into the case. After much head scratching and a few beers, we came to the conclusion that 150 engines sent to the factory for overhaul that were in need of a case must have been fitted with a 165 case with the smaller lifter holes.This made sense since I believe Franklin quit making 150s in 47 or 48 and the only cases they would have after that would be 165s.They must have pulled 165 cases off of the production line and had the lifter holes drilled for the 150, slapped a 150 data plate on and said good to go. I was telling an A&P this story a few days ago and he said that he had overhauled a 150 from a Stinson that had a 165 case with a 150 data plate and 150 lifters. He was also confused. It amazes me that there is no reference to it in parts books, overhaul manuals or service bulletins. Does anyone know if there is documentation on this ? Confused once again.____Grant.
Light case 150 Franklins Vs Heavy case 150.
- Thread starter gjordan
- Start date
cglucas
New member
Grant that is exactly what happened, and Franklin did not do much in the way of documentation. There were actually more different 150 cases than 165. I have had several of the heavier 150 cases with an 18905 and 18906 part number. They make a near bullet proof 150. The lower rpm of the 150 just makes it hard to tear one up. Greg
Thanks Greg! It is nice to know that my theory wasnt just my hot air. It makes me wonder just how much Franklin information has been lost over the years? When some of the old timers that worked for Franklin passed on I am sure valuable information went with them. In my quest to find some kind of documentation to use 165 valves in a 150 I talked to a fellow that is sending me a copy of an STC to convert a 150 to a 165. I was very skeptical of it being legit because of the history of the light case 165s. Now I am betting that it will say only 150s with the heavy case. I am hoping that our IA can submit the STC with a 337 to just use the top end modifications(valves, guides, and rockers) so we can finish topping our 150. I will post when the STC arrives.____Grant.
The STC arrived that supposedly changed a 150 to a 165 and it doesnt really do that. What it does allow is the substitution of the 165 valve train in place of the 150. It is everything from the cam on up to the valves, or almost everything. It finally ends up using 200 HP helicopter exhaust valves. I think these are the valves that were used before the helicopters switched over to the sodium filled valves. Probably the same valve as a 165 but a different number. This STC was done in 1981 which is modern compared to most Franklin information, but the supply of 150 valves was dried up by then and the 165s were getting scarce. There were probably lots of surplus helicopter parts available. This doesnt allow for increased RPM or the use of the 165 induction system and bigger carb. It requires a slight modification of the 150 lifters and removing enough metal from the case to clear the higher lift 165 cam lobes. This might give you a few extra HP, but revving a 150 over its original red line would more than likely cause the same case cracking as the early 165s went through. All in all very interesting, but who knows what valves are available now. ___Maybe Larry L can post a copy of the STC? My computer skills are too limited.____Grant.
Just to bump this 3 year old thread, Larry L has discovered another type of heavy case 150. Talking with him yesterday, he said he cleaned up a 150 case and discovered it had the 165 light case casting numbers, but a 150 data plate. In line with what Greg confirmed, they must have pulled 165 cases off of the line and drilled the lifter holes for the 150 size and replaced a damaged 150 case. The only way that could have happened (I assume) is that this was done during the short period of time that Franklin was building the early 165s, but had quit building 150s. If I add the rumored very early 150s that supposedly didnt have the hole for the fuel pump rod , that makes 4 different potential 150 cases and not anything in any book I have ever seen that explains it all. Franklin History should be called FRANKLIN MYSTERY!!!!! Just another tid bit of info. _____Grant.
blimpy
New member
Hmm.. wish there were casting part numbers to go with each of these variations.
I have a 150 which is logged as an "exchange engine" supplied by Sacramento Sky Ranch ( in the 70's if memory serves),
when they were an Authorized Franklin Dealer, as well as being an outstanding engine repair station.
It would be interesting to me to know when AC Motors stopped overhauling engines in house, and this became
strictly a field overhaul situation.
My engine has about 1000 SMOH ( maybe 2000 TT? I forget).. has had a couple of cylinder topped, and has perfectly normal oil pressure, CHT's and as far as I am concerned should run many more years, with an occasional cylinder OH, and other
routine TLC. When the push rod seals go in.. we'll know better the true oil consumption.. but I figure it will then be on a par with comparable aged cont's and modern lycs.
Is this other folks experience with overhauls done when all parts were still available ? :?:
I have a 150 which is logged as an "exchange engine" supplied by Sacramento Sky Ranch ( in the 70's if memory serves),
when they were an Authorized Franklin Dealer, as well as being an outstanding engine repair station.
It would be interesting to me to know when AC Motors stopped overhauling engines in house, and this became
strictly a field overhaul situation.
My engine has about 1000 SMOH ( maybe 2000 TT? I forget).. has had a couple of cylinder topped, and has perfectly normal oil pressure, CHT's and as far as I am concerned should run many more years, with an occasional cylinder OH, and other
routine TLC. When the push rod seals go in.. we'll know better the true oil consumption.. but I figure it will then be on a par with comparable aged cont's and modern lycs.
Is this other folks experience with overhauls done when all parts were still available ? :?:
If the replacement case was a factory modified 165 heavy case, the casting # will be 18905 and 18906 for the two sides of the case. If it is a modified light case, the numbers will be almost the same, but the 9 in the heavy case will be (I think a 5) different. If it is a 150 case, casting numbers will be 17516 and 17515. Even the modified light case should be fine in a 150 application, since it is a little heavier than a regular 150 case. It just wasnt strong enough for the extra 200 RPM of the 165. I think you will need a mirror and a bright light to find the casting numbers on an engine that is in the airframe.
Larry Lowenkron
Member
Oops, I responded to this in the wrong string. Anyway, Grant pretty well covered it. Just to be redundant...again, here is what I wrote:
The casting # for the engines is located below the #5 and #6 cyl. For 150's it's "usually" 17515 & 17516. For 165 Light case it is 18305 and 18306. HC's are 18905 and 18906. Check your parts list and you'll see them there. Also might want to check out AD 51-15-02 for ref.
Sounds like you guys are getting a taste of the rain in the Willamette Valley (and then some!) Try and stay dry...but for sure, keep your wings dry!!!
The casting # for the engines is located below the #5 and #6 cyl. For 150's it's "usually" 17515 & 17516. For 165 Light case it is 18305 and 18306. HC's are 18905 and 18906. Check your parts list and you'll see them there. Also might want to check out AD 51-15-02 for ref.
Sounds like you guys are getting a taste of the rain in the Willamette Valley (and then some!) Try and stay dry...but for sure, keep your wings dry!!!
