Author Topic: Need expert advice - newbie poster  (Read 1512 times)

tecrousore

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Need expert advice - newbie poster
« on: August 31, 2013, 07:05:46 PM »
Hello all, New poster to the forum. I have been reading and following discussions for a while now.

I have a FL350 that i got for my wife. Had it several years and only had minor issues with it until now.

I got a 38 mm Mikuni carb from Randy at Odyssey Salvage a while back. Replaced the stock reeds with Boysen reeds and rebuilt the stock fuel pump.

I have done the oil passage mod to prevent the oil from getting into the starter which I had to replace when I got the Oddy.

My issue is this. At the beginning of last week it was running fine. In the middle of the week I replaced all four tires and took it out for a test run with the new rubber. It bogged at half throttle and would not build rpms past half throttle. I thought I might have some trash in the fuel so I cleaned the carb and checked the fuel filter. It still ran the same so I immediately checked the compression and it was at 115 psi.

The next day I was playing with it to figure out what the issue was. I started it and the same thing. Would not rev past half throttle and would bogg past half throttle. I checked the compression again and it was at 100 psi.

The next day I went to start it and it would not start. Checked for spark, good. Checked compression again and it was at 70 psi.

I have since removed the engine and tore it down. The cylinder is glazed but only had a bit of light scorching to either side of the exhaust port. The top ring was bypassing just to the right of the alignment pin in the groove. There is no scarring or excessive wear on the piston.

I noticed quite a bit of play between the piston and the cylinder. Then I got the micrometer set out and got really confused.

The piston is at 78.35 mm.  The bore is at 78.58 mm. The end gap of the rings is at 3.02 mm.  The exhaust bridge has not been relieved.

That makes the clearance between the piston and cylinder at .23 mm.

I read the the standard bore was 78.5 with .05 for piston clearance. Is that correct?

I am thinking that someone rebuilt this thing with a new sleeve in the cylinder and put the wrong size piston in it and the rings wore out really fast.

Am I way off base here?

Also, I would like to rebuild the top end, but don't really want to bore it out to 80.00 mm to put the wiseco piston in it.

What is the likely hood of finding a stock piston (78.5 or 79.0) and rings to rebuild this thing with. Can anyone give me a lead as to where I might find them?

Any and all comments are welcomed.

Thanks in advance for your assistance.

Troy

shoubadaba

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Re: Need expert advice - newbie poster
« Reply #1 on: August 31, 2013, 07:20:06 PM »
I and welcome sounds like its never been rebuilt. It sounds like its just worn out. Honda offered a 78.75 over bore piston and a 79 mm the likely hood of finding a piston and rings new is gonna be next to impossible. Just order a 80mm wiesco and have it bored to .05 clearance. Stock was .06 clearance and the stock endgap service limit was 0.5. After you go 80mm you still have all the way up to 82mm
« Last Edit: August 31, 2013, 07:21:40 PM by shoubadaba »

hoodlum

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Re: Need expert advice - newbie poster
« Reply #2 on: September 02, 2013, 11:24:44 AM »
I know it's a personal preference, and some say one thing while others say something else, but me personally, I would not bore to .005 clearance with a wiseco on an air cooled engine... I had a 350 once and rebuilt with a wiseco, relieved the bridge, and bored .005 over... It lasted about 30 minutes before the piston seized... I cleaned the piston, put in new rings, and bored it another .002, giving .007 clearance, and never had another problem.... I made sure to let it warm up before running it hard to reduce the risk of piston slap, but that was it..... Just keep in mind that the larger of a piston you put in, the amount of expansion will be more because there is more mass....
You also need to measure the entire bore  with a bore guage before finding a stock size piston... If it is a worn out stock piston, I would be willing to bet that the bore is worn uneven... It needs to be measured at different points up and down the bore to verify this... If it is, your new piston won't last long either....
Hoodlum

LiveWire

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Re: Need expert advice - newbie poster
« Reply #3 on: September 03, 2013, 07:32:26 AM »
Stock was .004" with .006" being the service limit. I run .005", but teflon coat the Wiseco's like the OEM pistons were. This is on an otherwise stock engine. Any mods and you need more clearance or water cooling. Windowing the intake side of the piston also helps to keep the piston cool and reduces expansion.

hoodlum

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Re: Need expert advice - newbie poster
« Reply #4 on: September 03, 2013, 10:59:07 AM »
Oh yea... You need to have the cylinder checked first, then order the piston based on the amount it needs to be bored to straighten everything out... Otherwise, you may be stuck with a piston you can't use....
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shoubadaba

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Re: Need expert advice - newbie poster
« Reply #5 on: September 03, 2013, 09:23:04 PM »
Ill check what the manual says
« Last Edit: September 03, 2013, 09:25:56 PM by shoubadaba »