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Discussion Starter · #1 ·
Hi again, posted about my TRX 300 noisy engine in the newbie section. The story continues. I spent an evening listening to top and lower parts of the engine with a bar to my ear. Still sounded top end to me, but i was truly not sure, Had one of those begger it!! Moments, And decided to take the engine out the bike and get it back on the bench where i feel happiest. Long story short, thats where it is now. Head and barrel off, i proceeded to check out the rod bearing (as you call it) I was surprised and delighted to find it was really good!! no noticeable movement at all. Better than i could hope for. I pushed out the wrist pin and tested this as it says in the haynes manual, by pushing it in to the small end bearing and giving it a waggle. In the picture in the book, it shows the pin just in the small end of the rod. This is how i tested it last time i had the engine out. At this point the pin looks as though it is reasonably in limits. As i was doing it i could see the centre section was marked and warn! Obviously.... Well it is now, thats where it should be tested! not on the ends that sit in the piston and dont move!! eureka. I pushed the pin to the middle and rocked it there, and it is as slack as a slack thing. I am now hoping this will be the problem and the cause of the noise? My question is. I have the chance of a used piston and pin for what would be about 30 of your dollars. I am not too sure as yet what a new pin would cost. But would it be best to get the new pin in the hope it will take up more of the slack, if any that is in the small end of the rod? Thanks....Pete.
 

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I think I would go with the new pin. In the US, they're about $20. Another used pin might also be worn in the center.
 

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Discussion Starter · #3 ·
Ye... Your right i think, just got to hope the small end is not too badly warn now, if its not too bad this will be a good result for me!! Not too sure if it was you or someone else on here that said to persevere with the old gal... but i am glad i did now!!! so thanks to you or whoever for the push!
 

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seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing...no sinse is tearing it down again. i would like to know something..when you took the head off..and pulled the cylinder..and got to the piston..was there any nicks..marks from the valves hitting the piston ?..if there was..make sure you check your valves..and see if they got bent ?..you can check this by putting them into a drill chuck..and watching the valve..to see if it got bent ..if they did get bent..better replace any bent valves. this would be a good time to fix this..if there is a problem with your valves...if you don't have a drill handy..install the spark plug...turn the head upside down < do this outside an away from any sparks > !!..pour some gas down into the head..if you have any bent valves..the gas will leak through the valves.
 

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seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing
What wrist pin bearing? It's a 4 stroke.
 

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seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing
What wrist pin bearing? It's a 4 stroke.
should be a wrist pin bearing in where the piston pin goes through..yes..no ?..more like a needle bearing
 

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seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing
What wrist pin bearing? It's a 4 stroke.
should be a wrist pin bearing in where the piston pin goes through..yes..no ?..more like a needle bearing
A 2 stroke has a wrist pin, but not a 4 stroke. The pin just slides through the hole in the rod.
 

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yeah..your right..sorry..had a helmut moment..lol..dang..been a long day..lmao
You'll be OK...................I think. LMAO.
 

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yeah..your right..sorry..had a helmut moment..lol..dang..been a long day..lmao
You'll be OK...................I think. LMAO.
at least i know my clutches !!..lmfaoooo !
Yeah, but you want be able to use a clutch if you try to put a wrist pin bearing in a 4 stroke. LMAO.

No, it's OK, I forget sometimes too. Must be old age. LMAO.
 

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Discussion Starter · #14 ·
seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing...no sinse is tearing it down again. i would like to know something..when you took the head off..and pulled the cylinder..and got to the piston..was there any nicks..marks from the valves hitting the piston ?..if there was..make sure you check your valves..and see if they got bent ?..you can check this by putting them into a drill chuck..and watching the valve..to see if it got bent ..if they did get bent..better replace any bent valves. this would be a good time to fix this..if there is a problem with your valves...if you don't have a drill handy..install the spark plug...turn the head upside down < do this outside an away from any sparks > !!..pour some gas down into the head..if you have any bent valves..the gas will leak through the valves.
As was answered, there is no bearing, I so wish there was! On top the piston there are two indentations, i think they are on the piston from new as the picture in the manual has them. They look like they have no new marks in or around them so i can only assume the valves are not hitting them. I will take the valves out and check them as you suggest, as i am looking to do as much as i can now the engine is out. Its a real heart sinker to get the engine back in and the dreaded fault still being there!! as i know from last time. any tips like this i am more than glad to get. more i can do now more chance i can have of it being ok. One good thing from all this. I got the engine out in a good time. partly the nuts were all greased as i put it back last time, but knowing what you are doing is a wonderful thing!
I have measured the inside diameter of the small end bearing surface and it is a shade over the limit in the manual. I measured it with inside calipers and a micrometer. all down to feel i know but it is over i think. I can only hope the new pin will go some way to taking this slack out. What are your thoughts on getting a larger pin and machining pin and rod?
 

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seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing...no sinse is tearing it down again. i would like to know something..when you took the head off..and pulled the cylinder..and got to the piston..was there any nicks..marks from the valves hitting the piston ?..if there was..make sure you check your valves..and see if they got bent ?..you can check this by putting them into a drill chuck..and watching the valve..to see if it got bent ..if they did get bent..better replace any bent valves. this would be a good time to fix this..if there is a problem with your valves...if you don't have a drill handy..install the spark plug...turn the head upside down < do this outside an away from any sparks > !!..pour some gas down into the head..if you have any bent valves..the gas will leak through the valves.
As was answered, there is no bearing, I so wish there was! On top the piston there are two indentations, i think they are on the piston from new as the picture in the manual has them. They look like they have no new marks in or around them so i can only assume the valves are not hitting them. I will take the valves out and check them as you suggest, as i am looking to do as much as i can now the engine is out. Its a real heart sinker to get the engine back in and the dreaded fault still being there!! as i know from last time. any tips like this i am more than glad to get. more i can do now more chance i can have of it being ok. One good thing from all this. I got the engine out in a good time. partly the nuts were all greased as i put it back last time, but knowing what you are doing is a wonderful thing!
I have measured the inside diameter of the small end bearing surface and it is a shade over the limit in the manual. I measured it with inside calipers and a micrometer. all down to feel i know but it is over i think. I can only hope the new pin will go some way to taking this slack out. What are your thoughts on getting a larger pin and machining pin and rod?
I personaly would go ahead and buy new ones. It would scare me that it still may not be right after you get it machined.
 

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Discussion Starter · #16 ·
seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing...no sinse is tearing it down again. i would like to know something..when you took the head off..and pulled the cylinder..and got to the piston..was there any nicks..marks from the valves hitting the piston ?..if there was..make sure you check your valves..and see if they got bent ?..you can check this by putting them into a drill chuck..and watching the valve..to see if it got bent ..if they did get bent..better replace any bent valves. this would be a good time to fix this..if there is a problem with your valves...if you don't have a drill handy..install the spark plug...turn the head upside down < do this outside an away from any sparks > !!..pour some gas down into the head..if you have any bent valves..the gas will leak through the valves.
As was answered, there is no bearing, I so wish there was! On top the piston there are two indentations, i think they are on the piston from new as the picture in the manual has them. They look like they have no new marks in or around them so i can only assume the valves are not hitting them. I will take the valves out and check them as you suggest, as i am looking to do as much as i can now the engine is out. Its a real heart sinker to get the engine back in and the dreaded fault still being there!! as i know from last time. any tips like this i am more than glad to get. more i can do now more chance i can have of it being ok. One good thing from all this. I got the engine out in a good time. partly the nuts were all greased as i put it back last time, but knowing what you are doing is a wonderful thing!
I have measured the inside diameter of the small end bearing surface and it is a shade over the limit in the manual. I measured it with inside calipers and a micrometer. all down to feel i know but it is over i think. I can only hope the new pin will go some way to taking this slack out. What are your thoughts on getting a larger pin and machining pin and rod?
I personaly would go ahead and buy new ones. It would scare me that it still may not be right after you get it machined.
I have still got the same problem if i put a new 17mm pin in and its too slack because the bore of the rod is oversize. I am back to the same dilemma of getting a new crank and rod now, all for a warn small end. I just wondered if there was a over sized pin, that with some machining of the piston, and some work on the small end of the rod in place, could be got to fit to a good tolerance? I think most people just get new parts? not too sure i fall in to the most people category!!!
 

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The only problem is it will be hard to find the exact center of the hole since it is wore. So enlarging it for a larger pin will be pretty hard IMO. But if you can somehow find the right lenght to dertermine the exact center it "could" work I suppose.
 

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Discussion Starter · #18 ·
The only problem is it will be hard to find the exact center of the hole since it is wore. So enlarging it for a larger pin will be pretty hard IMO. But if you can somehow find the right lenght to dertermine the exact center it "could" work I suppose.
I cant help but think it can be done, with a reamer or something similar, I have got a mate coming over for a beer tonight, just by chance he is a machinist!! I will put the question to him see what he come up with. Its a public holiday here in the UK so no chance of getting any parts anyhow. best to use the time to give it some thought. Thanks to all the above for the words of wisdom, it really is a help....... Pete.
 

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I really hope you can get it together without buying a new crank. And if your friend figures out how to find the dead center of the hole to enlarge it let us know how he did it. Good luck!!
 

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Discussion Starter · #20 ·
seeing how your going to replace the wrist pin..you may as well replace the wrist pin bearing...no sinse is tearing it down again. i would like to know something..when you took the head off..and pulled the cylinder..and got to the piston..was there any nicks..marks from the valves hitting the piston ?..if there was..make sure you check your valves..and see if they got bent ?..you can check this by putting them into a drill chuck..and watching the valve..to see if it got bent ..if they did get bent..better replace any bent valves. this would be a good time to fix this..if there is a problem with your valves...if you don't have a drill handy..install the spark plug...turn the head upside down < do this outside an away from any sparks > !!..pour some gas down into the head..if you have any bent valves..the gas will leak through the valves.
As i said in an earlier post there are valve sized marks on the piston, I thought this was cast in to the piston from new? as it is on the one in the manual.? On your advise i took out the smaller of the valves to check it in the drill. It is bent! not by much, but it is, could be a contributing factor to the tapping noise for sure. I did not check the other as i was pressed for time.
The thoughts on the piston were that it could be done with a tapered reamer. My mate is going to give it more thought and maybe come back with a method. I will pass it on if he comes up with a plan. To be honest he is not too impressed with steel running in aluminum and was a bit dismissive about the whole set up of the engine. He likes roller and ball bearing and his view was that when these engines are shot you throw them out and get a new one. (a long way from my thoughts) I will have to keep this in mind if i decide to go with his ideas for boring the piston and rod as i am not sure his heart was in it and he may be thinking, that will do! We will see.
 
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