motor problems knocking

[custom R]

I went riding today and I just put a new pipe on and new reeds ,race gas dome, comp was about 200 and the pilot was a little small so i put a 52 in from a 50 and it seemed ok pulled very hard temp was 160 and was running great all day and I went for one last quick ride and right when i got back it started knocking it sounded like it was coming from the top end it was vibrating a little but not horrible I cut it off right away the compression felt ok I kicked it once and it started up and was still knocking so I shut it down again but I didnt want to let it run so I couldnt really tell where it was coming from and I did notice the pipe was discolored and looked like it got pretty hot where it comes from the cyl down to the first bend in the pipe on the inside It was cold outside so it might have leaned out a bit

my setup is a esr 310 with porting done by precision powersports, a 4 mill stroker crank it is a hotrods crank so im kinda thinkin that might be the problem, a esr trx 9 pipe, 38 mm carb,rad valve w/ carbon fiber reeds, rpm adj, timing plate

any suggestions on what the problem is also if my timing is advanced too far would it make it kick back and hard to start, the motor only has about 40 hours on it since being built with all nrw bearings and seals, crank, and new top end

[GOTFEAR]

maybe the counter balancer or piston slop on bottom off the cylinder

[86 Quad R]

remove the plug and see what it looks like for starters. note the color, look for signs of aluminum or other debris on it.

there could be one several things going on. skirt slap from cracked skirt, big rod end, wrist bearing, ect ect

[custom R]

I pulled the plug it looks good, good , kinda dark tan color, im gonna pull the top end tonight and take a look

[custom R]

ok so I went to pull off the top end and I think i found my problem one of the base studs was broke off so im thinkin it was piston slap that I was hearing and correct me if im wrong. I pulled on the connecting rod and piston and both feel tight so do you think I got lucky and its just the stud thats the problem.

I think im gonna go ahead and get a new piston and a bore job while its off since im not sure how long its been broke everything looked ok but it seems like there a little too much movement between the piston and the cyl and I think I got about 30 or 40 hours on the topend anyway

anything else I should check out while it apart

[riderssb250x]

check your crank while your down there make sue it doesent rock left to right or move oup and down and replace the wristpin bearing..

[C-LEIGH RACING]

?????? Head stay ???
Go ahead & replace all 4 case studs.
Neil

[custom R]

I checked the crank out and it was within honda spec's so I feel good about that. I took the cyl to the machine shop and he had to bore it out from 72 mm to 72.50 to get it to clean up so it was pretty worn. im surprised it still had good compression' it was at 200 exactly where it was when I put it together.

I have a headstay and I put the bolt in but I don't tighten it all the way Should I crank it down or not I've herd both ways.

I did get real lucky though the piston had a crack on the skirt so it could have got real ugly

[riderssb250x]

if you don't mind me asking what are the factory specs for the crank to check it iv got my topend off and id like to check it also lemme know thanks!

[C-LEIGH RACING]

Originally posted by custom R
I checked the crank out and it was within honda spec's so I feel good about that. I took the cyl to the machine shop and he had to bore it out from 72 mm to 72.50 to get it to clean up so it was pretty worn. im surprised it still had good compression' it was at 200 exactly where it was when I put it together.

I have a headstay and I put the bolt in but I don't tighten it all the way Should I crank it down or not I've herd both ways.

I did get real lucky though the piston had a crack on the skirt so it could have got real ugly

Yeah, guess you better crank it down.
I ran ours for quite a while without the head stay & was a long time before had any problems, but after one engine broke two studs on the same side I decided it was best to put it back in place.
Any amount of compression over 200lbs, I would bolt up the stay just to be safe.
Running without it though, will free up the top end some far as revving it.
Neil

[Honda 250r 001]

the 250r just sounds that way. if it only happens at idle. i dont know what it is but if you run a forged pisotn i guess its worse than running a cast.

[custom R]

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if you don't mind me asking what are the factory specs for the crank to check it iv got my topend off and id like to check it also lemme know thanks!
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I think its .040 max but im not positive I cant find my book right now but when I checked mine I called the machine shop and he said mine was fine at .027


The knock was not the normal R knock it was loud. but I think I got it worked out Im hopeing to get it back together next week so we will see

timing ???????? should the piston be at tdc or real close when the magnet is at the pickup mine seems like its about 2 inches past it with the rod all the way up I dont have the topend here its at the machine so I dont have it on to see but its seems kinda off to me maybe the flywheel key is broke