av8tor1977

My Feedback: (6)

I bought an engine from him years ago and was very happy with the purchase/service.

AV8TOR

Twin Star

I have a question on the intake port timing. If the bench mark timing for the exhaust is 140 - 150 degrees.

Is there a benchmark timing for the intake port.

w8ye

My Feedback: (16)

I made several different purchases from Dave Carr back in the late 90's. talk to him on the phone several times also.

Everything was always up front and as advertised.

av8tor1977

My Feedback: (6)

140 works pretty well for our purposes, maybe 130 for big props and/or operation below 8000 rpms. 150 might be a touch high... In any case, be sure to use a stack on the carb inlet, as increased intake port timing leads to increased "stand off" or reversion, and the velocity stack helps contain some of that.

It's just like a car engine, if you get too radical with things, the engine becomes a pain to "live with", even though it might make really good overall power.

AV8TOR

Twin Star

Well, I measured the intake timing on the 30 I'm working on and the intake timing is already 150.

w8ye

My Feedback: (16)

All this timing information and comparables with different make engines is all on this conversion forum if you can just find it. I've seen it many times before.

w8ye

My Feedback: (16)

I did a search with the search engine at the top left and searched just the Conversion Engine forum. It just went back through the ASP program days and stopped before the VBulletin Days in the summer of 2003.

The search engine at the top right looks at all of RCU
http://search.rcuniverse.com/search....archwhere=both

Google results
http://testfly.0catch.com/homelite/e...lindermod.html
http://www.modelpowerboat.com/forum/...-rc-engine.htm
http://rcfaq.com/ANSWERS/ENGINES/TIMING.HTM
http://powerpete2.20megsfree.com/photo2.html

This is a boat engine tuned too high for airplane
.020 head clearance , cylinder has had the gasket removed and the cylinder lapped in to the block for perfect seal. Exhaust port timing is 168 degrees , Intake timing is 152 degrees , Transfers are matched to block and widened .Piston has been lightened , flywheel has been lightened and balanced , new 167 big bore carb, intake matched to cylinder
http://www.youtube.com/watch?v=WvLBpux8pJA

av8tor1977

My Feedback: (6)

Sounds pretty good. He needs to work on his pipe coupler though... See the pipe move out when he "zings" it?? Or is that a "variable length automatic tuning pipe"?

AV8TOR

w8ye

My Feedback: (16)

That was part of his advertisement to try and sell the engine in the RCU market place for $275

I see that pipe not only move in and out but spin around too.

Twin Star

The reason I wanted to ask about the intake timing is, I thought it was already kind of high on my engine.

From what I've read, the general consensus was intake timing 120 -130. I'm not even sure how correct that is.

Well, I'm not going to even touch the intake timing, I think it's best left alone.

w8ye

My Feedback: (16)

I came to the same conclusion

av8tor1977

My Feedback: (6)

Yes, just run it at that. The only way to change it would be to raise the cylinder, and that would lower the compression which would definitlely cost power.

AV8TOR

av8tor1977

My Feedback: (6)

Also, I keep forgetting to mention. www.lambertsrc.com is also a great place for conversion accessories.
AV8TOR

Twin Star

I have a question about the piston in the Homie 30. Does the long skirt go to the intake or the exhaust side. Also there is a "dimple" on the con rod and it currently faces to the front of the engine.

I got to thinking that maybe the piston is installed backward, causing the intake timing to be at 150, that seems higher than usual.

av8tor1977

My Feedback: (6)

Well, a piston with a short skirt would definitely raise the timing of the intake. The piston goes whichever way that puts the ring gap clear of all ports, and that usually ends up somewhere approximately opposite the exhaust port. Sometimes there is an arrow on the piston that faces either forward, or sometimes towards the exhaust port. What is most important is where the ring gap ends up.

AV8TOR

Twin Star

Say I can turn the piston either way and have the ring gap clear of the ports and I have my choice of 120-130 and 150 degrees intake timing, depending on which way I turn the piston. Which should I choose if I intend on using a 17" or 18" prop.[sm=72_72.gif]

av8tor1977

My Feedback: (6)

I would go with the lower intake timing if you are really sure the ring gap will be clear.

AV8TOR

Twin Star

I reversed the piston in my Homie and checked the intake timing. I got 132 degrees with the long skirt on the intake side, instead of 150 with the short skirt. One other thing, the long skirt is chamfered on the bottom edge, like it probably should be, going over the intake port opening, were the short one isn't. Also, on the piston just off center, but in line with the wrist pin is a "B" stamped on the top of the piston. Could that stand for, "back of engine"? The ring gaps run between the exhaust port and transfer ports with the piston reversed from the way it was. So I think that is ok.

So, what do we think. Should the piston be reversed from the way it was?

w8ye

My Feedback: (16)

Yes

Twin Star

NO !!! I did some more checking and found with the piston reversed, the short skirt opened the exhaust port at the same time as the intake port.

w8ye

My Feedback: (16)

You may meed a new piston?

captinjohn

Lookat the color of the piston real good ...inside & out...the more colored from heat side will go toward the exhaust...most likely! Capt,n

Twin Star

I finally finished the new twin outlet muffler for the Homie. I had some "paying" projects to finish first.

Well, no improvement in RPMs but it is louder with the new muffler. Well, I think it is safe to say the exhaust is as good as it can be.

Twin Star

I purchased a practically new Homie from Ebay awhile back. The ad said it was a 25cc but I took the muffler off today and theres no divider in the exhaust port. Is it possible this engine is really a 30cc.

av8tor1977

My Feedback: (6)

Measure it to be sure, but as far as I know all 25cc Homeys had the exhaust port divider, and the 30cc engines did not. I have seen engines improperly "badged" with the wrong displacement, especially the Homelites 25/30cc series.

Handy formula: bore x bore x stroke x .7854 = displacement. Measured in inches, this gives you cubic inches. To get cc's divide that result by .061

(Down and dirty quick check....) You can get pretty close on an engine by measuring the full stroke through the plug hole with a calipers, and then inserting a pencil into the exhaust port, reaching over touching against the opposite cylinder wall. Turn the piston till it marks the pencil as it pushes it up against the exhaust port. Pull the pencil out and measure to the mark.

AV8TOR