Briggs Raptor alcohol to gas conversion question
- Thread starter Daniel Coop
- Start date
- Tags alcohol conversion gas question raptor
in the first place a stock raptor aren't that impressive , I got a Tecumseh 5 hp that will spank one . The Dover motor you have was it electric start or pull start ? These Briggs with the right cam in them can be a bear to pull . That old cover and recoil my not last long . Also if the recoil requires the easy spin thing that works as a crank bolt , they will not hold up to high RPM's .
Daniel, don't mind David, he drinks too much of the Tec Kool-Aid!
I have a .290 lift cam in a flathead, and yes, it can be hard to pull...BUT! You need to make sure it is on the compression stroke when you do pull it. If it kicks back, it'll hurt ya!
David is correct in regards to the starter clutch. Unless you service it, it can cause problems. On my big cammed flatheads I adapt a late model cup type starter to them. I like the old rounded shrouds as well. Cut the end off the crank and put the cup on there. Not perfect, but will work better!
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I have a .290 lift cam in a flathead, and yes, it can be hard to pull...BUT! You need to make sure it is on the compression stroke when you do pull it. If it kicks back, it'll hurt ya!
David is correct in regards to the starter clutch. Unless you service it, it can cause problems. On my big cammed flatheads I adapt a late model cup type starter to them. I like the old rounded shrouds as well. Cut the end off the crank and put the cup on there. Not perfect, but will work better!
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Thanks for all the great info guys. I'm a novice with these flat heads, and that's why I am posting this stuff, so that others may share their experience/wisdom with me. It showed up with a starter clutch on it, so they had to be starting it with a recoil. I still need to try to indicate lift on this cam and will report back.
Degree wheels are nice, because sometimes cam specifications are given at specific degrees of rotation. .050 comes to mind, as well as computing total duration of open valve, valve overlap, stuff like that. This is important if you want to compare an unknown cam with one available on the market. You'll find several completely different cams, with the same lift out there.
Well, because I am not an engine builder and don't have the experience or knowledge with these flathead motors, I shipped my motor to my friend and engine builder, Dan at Childish Concepts Racing, an avid kart racer and race engine builder out of Menomonee Falls WI. He received the engine via FedEx and quickly went to work on the rebuild. Here it is rebuilt with new rings and seals, new stainless valves and 20lb springs. The block was a little warped and had to be decked resulting in the piston popping out .027. A .050 copper head gasket is on its way to remedy the situation. This should make for a compression ratio of about 10:1 and "it should crack fairly well" in his own words. He found the cam to be a special grind "WKA stock class racing cam" with stock-ish Raptor motor lift and worked over duration. We have decided to leave the cam for testing purposes, but may decide to change it depending on how it performs with the slidedraft Mukini carb. I want a bulletproof, reliable, but fast engine that's not going to break my hand trying to start. He estimates with the current cam, to be strong up to 6500RPM. He's got an engine Dyno, so he'll be able to figure out HP #'s but most importantly properly tune and time the engine with it's new ARC billet flywheel. He also finalized the welds on the homemade intake but decided he wanted to make a support bracket for it. The block and head have also been sandblasted and some Briggs and Stratton Ice White paint is also on its way.
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Pull start is definitely the plan as the starter clutch the motor showed up with is in great shape. I had forgotten about this other recoil housing that was on a jacked up 5hp I paid $40 for before I knew any better and decided it was in even better shape than the one we were going to use. (No dents) I boxed it up along with an OE Briggs pull start handle and sent it off to WI.
Looking good. That valve angle looks Raptor to me. If you're anything close to Raptor spec on the cams, it will be easy to start with the recoil. Something to remember, is that when you spin these motors up to 6000 a few times, that recoil pawl system starts to get unhappy. I don't know if it's because that high RPM starts to sling the oil out, or what.
Once you've ran it a few times on the bike, be wary of the high pitched squeal. Take it back down and lube the balls as soon as you hear it, or you'll be replacing the pull cord too. Glad to see you progressing so well on this engine. Good job. It's going to be fun.:thumbsup:
Once you've ran it a few times on the bike, be wary of the high pitched squeal. Take it back down and lube the balls as soon as you hear it, or you'll be replacing the pull cord too. Glad to see you progressing so well on this engine. Good job. It's going to be fun.:thumbsup:
>>>Once you've ran it a few times on the bike, be wary of the high pitched squeal. Take it back down and lube the balls as soon as you hear it, or you'll be replacing the pull cord too. Glad to see you progressing so well on this engine. Good job. It's going to be fun.:thumbsup:<<<
Now that's a great suggestion for any rebuild of a vintage Briggs engine. Only caution is to make sure the starter cover is reinstalled securely (and evenly).
Now that's a great suggestion for any rebuild of a vintage Briggs engine. Only caution is to make sure the starter cover is reinstalled securely (and evenly).
True, I would hope everyone rebuilds and lubes the starter pawl during a rebuild. Daniel has his apart after all.
My point was that with a high RPM engine, you end up doing it again. And again. Those pawls do not like high RPM. Case in point, last raptor that went on my Tote Gote. I installed a cleaned pawl, even replaced a couple of the balls because they had some flat spots. Lubed with 30wt. Two hours of run time later, there is that squeal. I left it alone, it wasn't that loud. Next time I started it, it was louder.
Pulled the shroud, pulled the pawl, nothing wrong. Installed a new pawl, lubed it. Same thing a couple hours later. Pulled it, lubed it, all is well. This is the second high RPM flathead design that has done this. The other flatheads from 2.5 to 5HP I rebuilt and lubed them once, and never had a problem, running them on the governor. It is an issue with high RPM flatheads using the recoil start system.
My point was that with a high RPM engine, you end up doing it again. And again. Those pawls do not like high RPM. Case in point, last raptor that went on my Tote Gote. I installed a cleaned pawl, even replaced a couple of the balls because they had some flat spots. Lubed with 30wt. Two hours of run time later, there is that squeal. I left it alone, it wasn't that loud. Next time I started it, it was louder.
Pulled the shroud, pulled the pawl, nothing wrong. Installed a new pawl, lubed it. Same thing a couple hours later. Pulled it, lubed it, all is well. This is the second high RPM flathead design that has done this. The other flatheads from 2.5 to 5HP I rebuilt and lubed them once, and never had a problem, running them on the governor. It is an issue with high RPM flatheads using the recoil start system.
Looks great Daniel!
Here si where I am conflicted. I have always heard keep your balls dry, and your shaft lubed! Those balls need to be clean to work, but because the shaft rides inside the square part, and the square part stays stationary, that is where the squeal comes from...I always keep my balls dry, and my shaft lubed! Works for me!
Here si where I am conflicted. I have always heard keep your balls dry, and your shaft lubed! Those balls need to be clean to work, but because the shaft rides inside the square part, and the square part stays stationary, that is where the squeal comes from...I always keep my balls dry, and my shaft lubed! Works for me!
My Great Aunt Mary, who lived to 99 yrs young, enjoyed cocktail hour(s) every day. When asked her preference she always replied, "I'll have a high ball, low ball or no balls at all." She was quite the :devil2:.
Adding to Eric's otherwise informative observation:doah:, making sure the shaft is free of nicks, burrs and rust is also important. I sand the shaft extension with 220 wet before installing the starter. Just a little muck will cause a major headache.
Adding to Eric's otherwise informative observation:doah:, making sure the shaft is free of nicks, burrs and rust is also important. I sand the shaft extension with 220 wet before installing the starter. Just a little muck will cause a major headache.