That is exceptionally ugly.
2007 Yamaha Grizzly 350 low compression
- Thread starter nwjones18
- Start date
Yeah its bad.. And I'm finding the wrist pin is pretty well seized to the rod. I've tried the C-clamp and some sockets but no luck. Trying to think of a better plan than getting after it with my ball joint press.. I don't want to tear up the rod bearing.
Wow, that is a rough looking piston. Congrats on getting it apart and let it be known that a cheap top end kit has got to be a whole lot better than what you had, LOL. How did you get the piston off if the wrist pain is seized to the rod? Sorry for the question if there’s something obvious I am missing? Edit: Never mind, I believe the shop rag is under the piston and sitting on the jug as I look closer.
Last edited:
I just finished getting the wrist pin off and it was indeed seized to the rod.. I used the ball joint press and a deep socket slightly smaller than the pin.. I think this was at least part of the problem or maybe the result? They were pretty much welded together along a single line all around the inside of the rod right in the middle of the wrist pin. In some places its raised and in others its a grove. I'm thinking I'm just going to polish it as best as I can with a dremel tool, lube it up good and hope for the best. Anyone got any tips for getting this any better? I realize that replacing the Rod is the only right way to do this.. but that just isn't going to happen for a couple reasons: 1. Rod and crank are one assembly you order together, are expensive and require me to completely disassemble the engine. 2. Its an old 4-wheeler not a space ship. Thoughts?
I have put new cranks and rods into atv engines. Whole lot of parts, shims etc. If you are not up to the task ypu may wish to sell it as is. Finding a good used engine won't happen.
Of course now is the time to put a kz1000 engine in it.
Of course now is the time to put a kz1000 engine in it.
You think a hone like this would do any good?
Amazon.com: OTC Tools 7011-4 Flexible Ball Hone for Cylinders and Bores - 3/4" - 19 mm : Industrial & Scientific
Buy OTC Tools 7011-4 Flexible Ball Hone for Cylinders and Bores - 3/4" - 19 mm: Flex Hones - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
You have nothing to lose and everything to gain. Polish it up (the rod end), the wear mark is more area for oil to accumulate and you still have plenty of support for the pin in the rod that is undamaged. The area you polish is not going to amount to much in terms of negatively affecting anything, if at all. However I would go with a new pin which should be relatively easy to source or a decent used one. If you can't find a pin then polish them both as best you can but I think having an unmolested pin surface would work the best with the interior rod end surface once you've polished that. Polishing them both could potentially lead to very minute, yet relevant changes in the parts fit, in the scope of an internal combustion engine going thousands and thousands of revolutions a minute.
Does it use a needle bearing up there or does the pin ride right on the rod?
The pin rides right on the rod on this one.
It should slide in with fingers only. Should feel a perfect fit. Any slop and it will knock and break the rod.
I'd try to find a brand new piston pin if possible, then try to just remove the high spots very carefully (by hand if required) in the rod bearing surface and test fit the new pin quite often during the process until it inserts and turns easily with no real noticeable radial play. I'd say the pin to bearing clearance should be around 0.0001~0.0005 inch based on other bike service manuals (see attached - need to do the math with the dimensions).
If you have (or can find) the service manual for your bike, then verify piston pin to rod clearance. It's a pretty tight fit on all vehicles, and like Chris142 mentioned, should take a little finger pressure to slide the piston pin into the rod bearing.
Min clearance = 0.7875 - 0.7874 = 0.0001 inch.
Max clearance = 0.7877 - 0.7872 = 0.0005 inch.
If you have (or can find) the service manual for your bike, then verify piston pin to rod clearance. It's a pretty tight fit on all vehicles, and like Chris142 mentioned, should take a little finger pressure to slide the piston pin into the rod bearing.
Min clearance = 0.7875 - 0.7874 = 0.0001 inch.
Max clearance = 0.7877 - 0.7872 = 0.0005 inch.
Last edited:
Just got in my service manual yesterday.. Looks like .0002-.0009 with a limit of .0029 for piston pin to piston bore clearance. Kit comes with a new pin, so I'll see how that one fits before I do anything.
^^^ That's piston pin to piston pin bore clearance. What's the manual say about piston pin to connecting rod bearing bore clearance? It's probably about the same, but should manual should call it out too.
I noticed the post where I showed piston pin clearance was also pin to piston pin bore, not pin to con-rod pin bearing clearance.
I noticed the post where I showed piston pin clearance was also pin to piston pin bore, not pin to con-rod pin bearing clearance.
I thought the same thing.. But I sure can't find it called out seperately anywhere in either the specs, or in the repair sections.. The crankshaft specs only refer to the big end and the piston only talks about the pin to bore.
I would suspect the new piston pin will slip into the con-rod small end fine when starting it from either side of the bore, but may hang up as it gets near the center of the bore from the looks of the damage. That's where you want to carefully clean up any high spots (by hand) that interferers with the piston pin sliding all the way through at the same force needed. If there is some metal missing out of the con-rod bore that's below the bearing surface I don't think that will impact it enough to warrant a new rod.
Maybe you could use some masking tape inside the con-rod bore to protect where you don't want to remove high spots, and use some very fine sandpaper wrapped around a finger to knock down any high spots until the piston pin slips all the way through well.
Maybe you could use some masking tape inside the con-rod bore to protect where you don't want to remove high spots, and use some very fine sandpaper wrapped around a finger to knock down any high spots until the piston pin slips all the way through well.
I've done some testing on the old pin with a dremel and one of these wheels:
www.dremel.com
It removes practically no material and leaves a mirror finish, after working on the Pin for a good 30 min I was able to remove the high spots smooth out the edges of the groove and remove very little material. The old pin fits exactly as you described. slides in easily to the damage in the center of the rod and then stops. I think if i can get the damage in the rod cleaned up to where it slides through fine I'll be ok. I like the idea of putting some tape in there to protect the sides.
Dremel Tools - Rotary, Saws, Oscillating and more | Dremel
Find the right tool for your project. Since 1932, Dremel® has been helping Makers with its full line of versatile, easy-to-use tool systems that deliver the perfect solution for almost any project.
www.dremel.com
It removes practically no material and leaves a mirror finish, after working on the Pin for a good 30 min I was able to remove the high spots smooth out the edges of the groove and remove very little material. The old pin fits exactly as you described. slides in easily to the damage in the center of the rod and then stops. I think if i can get the damage in the rod cleaned up to where it slides through fine I'll be ok. I like the idea of putting some tape in there to protect the sides.
As has been said, be sure to only work the damaged area. As well, agreed that if it ends up a bit larger in diameter in the center, the undamaged outer bore areas of the rod end should provide proper pin support and stability without issue, IMO.
I did my first start today and it fired up and sounds really good. Only ran it for 8ish min varying the throttle some to let it warm up. I had my infrared heat gun on the cylinder head and I shut it off when I caught a temp around 250, but from what I'm reading that's not unusual for an air cooled engine such as this. Any idea what temps I should be seeing on the cylinder/head on this thing? It has a weep hole in the head you can crack open to ensure oil is making it up there and it is. Put 15w-40 delvac in it for this first run.
Similar threads
- Locked