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2005 Cyl on the 2004 motor,what mods?

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I seen on here the 2005 cylinder has a reshaped skirt, not a thicker skirt, that is supposed to hold up better.The cylinder is supposed to fit the 2004 cases. I have seen also something about a oil hole restrictor, one screwed in , one pressed that must be dealt with to work. 😢

What modifications must be done to fit the 2005 cylinder on to the 2004 motor? Pictures would be great also.

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I talking with one of the sale guys at my local dealer and he was telling me about several cases of the 04 cylinder sleeve failing prematurely. (to thin?) Not 1 case but several. He thought it would be "cheap" insurance to replace the replace the 04 cylinder with a 05 along with piston, rings etc. He said this was one of the few changes from 04 to 05 but you wouldn't hear Honda talking about this one because it would make them look bad missing such an errant design flaw.

I went to the service department and priced it out at around $340.00 and asked to make sure that he was quoting the 05 cylinder. He said they were the same part number. ServiceHonda had the same parts for about $240.00

Has anyone heard of cylinder sleeve failures? My guess is that as long as you change your oil religiously and DO NOT let it get low, the cylinder will be fine. These bikes only hold .73 quarts of oil and getting low would be a disaster.

Any feedback would be appreciated on this subject.

Dean

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I did a search and came up empty, but I do recall a thread where the conclusion seemed to be that the 05 cylinder is slightly different and bolts right into an 04 engine with no mods or issues. Some guy posted that his son had burned up their engine and that they had installed an 05 cylinder. Does anybody know if all of the historical data is available?

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You know, this confirms my suspicion that the search function is totally screwed up. Searching on the key word 'cylinder' didn't produce this thread:

https://thumpertalk.com/forum/showthread.php?t=195701&parentpage=13

EDIT: Wilkinson14's original thread asking the same question as this thread:

https://thumpertalk.com/forum/showthread.php?t=182810

Anyways, both Tuner and Wilkinson14 have successfully made the switch to '05 cylinders on '04 engines, despite the unverified bull$hit published in MXA and Dirtbike. Maybe each might pipe up and write some details on what exactly was involved. Wilkinson14 mentioned that he's running a different cylinder sleeve than OEM to take care of the oil squirter issue.

Chris.

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you haven't heard anything else from either of these two about the switch, so it makes you wonder. I asked the regional honda service rep when he stopped by my local dealer and he says you cannot do it

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I believe Tuner is running an '04 cylinder with a Thumper Racing big bore kit. He has switched to an '05 R head. Thats exactly what I am doing.

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The 05 has a new cylinder, cylinder gasket, head, and head gasket part numbers.

I'm suspicious about the compatibility of these parts. Has anyone confirmed at least the Head?

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My guess is that as long as you change your oil religiously and DO NOT let it get low, the cylinder will be fine. These bikes only hold .73 quarts of oil and getting low would be a disaster.

Dean

My son changes the air filter, oil-both engine and clutch every ride on his 04'. Oil filter every two rides. We just rebuilt the motor (slight mods) with over 45.5 hours on it. These hours include (17) races in which he ran two classes-4 motos. Both the top and bottom end were fully inspected and everything was fine! Cylinder was in great shape. We never had the "burning oil" experience that others complain about. By the time of our last inspection our right intake valve clearance had fallen to zero, so we figured it was a good time to rebuild before we messed things up too bad. He went through two clutches in this period. We've been stoked. It's been a great ride. From experience, we feel the minor maintenance of cleaning air filters and changing engine & tranny oil goes a long, long way!

I read the 05' doesn't fit the 04'. But I've heard different from our mechanic. We'll believe our mechanic.

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The 05 cylinder will bolt right on the 04 motor. The base gasket and head gasket are a different part number. I ordered one of each and could find no difference except for the coating of sealant they put on the gasket. 😢

04= 12191-KRN-671 base and 12251-KRN-671 head

05= 12191-KRN-731 base and 12251-KRN-731 head

Unfortunately I run a nikasil liner and did NOT compare the skirts of the 04 and 05 as far as clearing the wrist pin oiler in stock form. I KNOW mine clears. The next time I get my hands on them I will compare them in stock form to see what's up.

The head is a simple bolt on, but the 05 head along with the 05 cam is made for better low to mid than the 04. We still run the 04 heads because they flow better for OUR setup. It is the combination of parts you use that make the difference, and you need to use the one that makes the power where YOU like it to be! We try to make ours in the mid to top end, BUT we change our springs, valves, retainers and keepers way more often than most would care. Again this is MY opinion and setup and you know what they say about opinions. 😢

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so i have an 04 and my skirts cracked...can anyone give me a strait answer

on the cylinder from an 05 fitting on a 04?

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I got an 05 head modded to fit my 04 bike. When I get my head back from Eric Gorr, I'll take a few pics of how he modded it.

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I have heard that the 05 cylinder will fit the 04 engine, you just have to modify something to do with the oil squirter. I have also heard from someone on this forum that Honda pulled all the bad 04'cylinders off the shelves. They have supposedly fixed the cylinder skirt problems with the new cylinders that are available off the shelf for the 04. However, I am not sure about this. I would love to know for sure!!!!!!!!!!!

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I have heard that the 05 cylinder will fit the 04 engine, you just have to modify something to do with the oil squirter. I have also heard from someone on this forum that Honda pulled all the bad 04'cylinders off the shelves. They have supposedly fixed the cylinder skirt problems with the new cylinders that are available off the shelf for the 04. However, I am not sure about this. I would love to know for sure!!!!!!!!!!!

Yea, you just have to grind a groove for the oil squirter, and it will bolt on just fine.

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I placed an 05 cyl on the 04 cases. Used spacers in place of the cyl head, to torque the cyl down WITHOUT THE BASE GASKET! Stuck a feeler gage between the oil jet & cyl. Had plenty of clearance. (With the gasket installed the clearance is increased). Then I inserted a small drill bit (the same size as the hole in the oil jet) into the jet. This showed the direction of the oil spray. The projected path of the oil DID CLEAR the edge of the cylinder. ALL WAS GOOD! Raced it for a year with no problems. The purpose of this oil squirter is to lube the piston pin & to use oil to cool the bottom of the piston. As long as the oil hits in the general vicinity of the piston center line your good to go. The biggest issue is to make sure the cyl clears the brass jet so the cyl seats correctly.

Due to the possibility of the castings being a bit different from one to the next I suggest you go thru the same routine,, just to be sure. But, everything looked so good I would probably do the switch again with total confidence.

By the way, the cyl I fitted up had .015 inch removed from the base gasket surface to reduce the piston to head clearance. With a stock cylinder you should have more clearance than I had.

Happy motoing 👍

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Ok, let me just clarify this once and for all before this guy gets the wrong information.

The 05 head will bolt directly up to the 04. It does not need any modification

HOWEVER, the 05 cylinder will need the oil squiter modified to fit the 04 cases, which can certainly done by any professional machine shop. I dont think ive heard of any cases here on TT where the 04 skirt has cracked or failed. However, using a modded 05 cylinder can only benefit your motor and your wallet.

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