ChiefK

The attached PDF file will show you the exact engine, with specs.

ChiefK

jetpack

My Feedback: (1)

Would anyone be able to tell me what size Dynamix carb came with the .91 ? Thanks

I'm also looking for dimensions of the carb adapter for it, mainly the collar height and what size set screws. I've only seen general pictures of them. Is the inside stepped to match the carb bore diameter?

I am also starting to look at drilling my cases to accept bolt-on headers and wondering what the center to center distance the factory drilled them at. Mac's Products has some of them but not all.

below is my .91 that I am asking questions about. Its a marine version I am restoring from new. I just got a fuel pump for it and seeing how it fits. I would like to try it with a Dynamix.

Does anyone know what the red anodized Dynamix is all about? Is the red cover plate and filter just a filter or designate a specific type of carb?

ChiefK

I'm in process of disassembling a Webra Speed .61. Went fine until I got to the cylinder sleeve. It's too tight to remove by hand. How do I get it out without doing any damage to the crankcase?

ChiefK

redbiscuits

My Feedback: (6)

I always use a heat gun to warm the cylinder head up to allow the aluminum to expand, this will help with getting the liner unstuck. Some guys also throw them in an oven to do the same thing.

ChiefK

Thanks... I got it out with the "oven" process. But there's a surprise.... The crankcase I want to use is from a "parts" engine, and I want to use it because it has the factory holes drilled for a bolt-on muffler. But the two parts are not identical on the inside. The one with the "muffler holes" has a good size groove machined in the bottom of the crankcase, in line with the rotation of the connecting rod, apparently to give the con-rod some clearance. The other case does not. Could this be a long-stroke vs short-stroke issue? I'm thinking I might be better off having a machine shop drill and tap holes in the "new" case that doesn't have muffler holes, using the "parts engine" crankcase for location,depth, and tap thread details... thus avoiding any part swapping. What do you think?

ChiefK

ChiefK

Used the oven... 250 degrees, 7 minutes. Once I got the sleeves out I was amazed at how different the two crankcases were inside. Anyone know where I could buy a new cylinder/piston/con-rod?

ChiefK

Broken Wings

My Feedback: (20)

You could take a couple measurements and email Randy at Mecoa and see if the HB .61 gasket sets will fit.

ChiefK

Thanks... your suggestion worked just fine, but now having second thoughts about whether this is a basket case or not. A little background.... I got it used from the well known auction site. This Webra Speed .61 turned out it to be a Metric version... external appearance pretty much the same as USA version, 8mm crankshaft, beefier conrod, different design crankcase (a relieved area to allow the larger conrod clearance, different engine mounting pattern), don't know about the bearings. Had flown this engine maybe 50-60 times, most recently in the Dirty Birdy ARF. That flight ended early (about half way through) with a sudden engine failure from full throttle to dead (engine was not running too lean). Dead stick landing was successful. The engine appeared to have virtually no compression. It could not be restarted. Checked glow plug... it was OK. Took it home, looked at it the next day, and even cold, virtually no compression. I don't know if I should trash it or if a new piston ring would restore compression. Because it's apparently a Euro-version engine, not even much good as a parts engine. Any thoughts?

ChiefK

Hobbsy

My Feedback: (102)

I bought this old Webra .91 ringed engine about four years ago, it had really soft compression, I bought a new piston, ring and sleeve and installed them. The ring never seated and it never got better than very soft mushy compression. I ordered a Frank Bowman ring and installed it and just around to running it today. I mounted what I thought was a Pro Zinger 14x6 but after 32 OZ of fuel I couldn't get more than 8,500 rpm on WildCat 5% Premium Extra with 2.6 OZ of castor added. I thought, well this ring isn't going to seat either I let it finish off the second 16 OZ tank and took it in the shop. It turns out the prop is a 14x8 and the compression is very snappy. When flipped slowly it will go over center and easily whack you finger, only once of course. It holds compression just as well as my ABN .91 which has no leak down compression. Amazing what a good ring will do. I don't seem to have a 14x6 but found a 14x7 Scimitar, more tomorrow. Incidently I'm running a 9mm SuperTigre .90 carb.

computermonkey

My Feedback: (90)

Hobbsy, question is the ring a dyke ring? Mounted at the very top of the piston.

Hobbsy

My Feedback: (102)

No sir, it's a conventional ring, I have a .50 with a Dykes ring though, it's a Diesel conversion.

computermonkey

My Feedback: (90)

I'm running into the same issue with my Webra 91i P5 engine. When I first got the engine it didn't have quaut for compression. Now that I got about three 12oz tanks of gas through it the compression is starting to some up. It is turning a APC 14x8 at 9300rpm.

Just fyi the older speed 91 were not design to turn larger props and are more happy over the 10k rpm range. The last series of 91's called the P5 engines where design for lower rpms.

Hobbsy

My Feedback: (102)

Computer, when the P-5 is fully broken in it should turn an APC 14x12 at about 9,200 on 5% fuel. A 14x12 is the smallest recommended prop. You're right about old .91s they turn a 14x6 at or just blow 10,000 on 5% fuel.

computermonkey

My Feedback: (90)

fyi mine is the gas powered. It's been a pain until I figure out all of it's habits. I have it on a Tiger 60 arf. Real nice match.

Good luck on your 90 I'm sure it make you happy after it has time to run. Frank's rings are really good. After you hone the cylinder and give them time to seat and use good fuel I don't you ever wear that engine out.

dasquirrelisme

My Feedback: (81)

I always wanted to try out a Webra engine and finally got one today. Its a 80 2 cycle and I cant find an information on them. Can anybody tell me anything about them? Looks like a "speed".

pancake

My Feedback: (2)

great to find this since I own 3 120 and today started my old 61. on the 61 I've used a davis soundmaster muffler with a strap on which works well, but was wondering about some alternate muffler substitutes for the 61?

jimmba

Hello ,
I have an old 91 speed regular ring webra that was new when I bought it but no box or instructions. It was not drilled for muffler so I drilled and tapped it and installed a bisson Pitts style Webra 120 muffler. Before that I ran it on the bench for break in . Ran great , idled /transition to full throttle good. Mounted it on plane with muffler and it runs fine till nose is pointed skyward .... Instant die. I have a pressure line from muffler to tank vent. Carb has two needles , high speed needle on right facing motor is springy kind , low speed on left is part of rotating barrel throttle arm assy.
Was wondering if perry pump would help, also backplate has no boss for drilling and tapping for crankcase pressure.
Help! Thanks!

computermonkey

My Feedback: (90)

Just fyi, Bisson pitts mufflers do not offer very much pressure. I ended up running a Conley Perry pump with mine.

jimmba

Thanks! Did yours have raised boss in center of backplate or just flat?

computermonkey

My Feedback: (90)

Flat

Ernie Misner

Still, you should be able to make it run okay I think. Is the centerline of the tank fairly well matched up with the carb spraybar, or a little below it? Some folks have had success increasing the muffler pressure by crimping the ends of the exhaust down tubes slightly. Also, try adjusting the engine at full throttle when pointing the nose straight up and see if that helps.

computermonkey

My Feedback: (90)

Just fyi if you crimp the exhaust tube you lower the power of the engine. Higher back pressure equals lower power.

Ernie Misner

Correct back pressure does not result in lower power. Tuned pipes create much more backpressure than open face, no muffler at all, but there is a huge increase in power. It is all about the timing of the pressure wave that is sent back to the exhaust port to keep the fresh fuel/air charge from escaping while the exhaust port is still open. If a Pitts type muffler is not even creating enough back pressure for tank pressure that is not a good situation.

jetpack

My Feedback: (1)

You can try a Bru-Line air filter with a fine element. The carb will have slightly more vacuum which will help draw fuel. I wouldn't go buy one if you don't already have one, but if you have one already, give it a try.

computermonkey

My Feedback: (90)

Update on my 91 P5i, I finally gave on the stock ignition, cutting out at full throttle and to what I believe was the cause of my crash at take off.
Any way I now run it on two percent nitro and seven percent oil. I since switched out the stock muffler with a Jett 90 size muffler. It now turns around 96 to 9800rpm with a APC 15x8 prop.