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Old 10-28-2011, 09:50 AM   #106
ONandOFF
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Sweet success story!

Thank you for sharing your craft, Steve.
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Old 12-10-2011, 06:46 PM   #107
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It appears the countershaft has two sliding gears, and three free gears. Can someone help me identify the 5 different gears on the countershaft?



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Old 12-10-2011, 09:13 PM   #108
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http://www.justxr.com/jaw/gearbox.html
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Old 12-10-2011, 09:45 PM   #109
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Quote:
Originally Posted by mcma111 View Post
Thank you for providing that absolutely superb link, Steve. That link contained exactly the information I was seeking.

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Old 01-24-2012, 12:34 AM   #110
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Piston Clearance for bore/Head questions

Steve,

When you get the cylinder bored do you usually specify the piston to cylinder bore clearance or leave it up to the machine shop?

If so what is best for these motors?

I have an old cylinder I am looking to use on a build.

Also, if you have a cylinder head that was run hot (scuffing on center journal but no oil starvation elsewhere) would you consider it a good core? I would hate to repair the center journal only to have valve seat problems later. (BTW this motor suffered from a particularly noisy head gasket failure near the exhaust valve, I swear it sounded like a valve seat loose or rod knock). For reference the bare cylinder head from Honda is $400 or so.

Thanks and great writeup.

Andy
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Old 01-24-2012, 04:53 AM   #111
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XRL Head

Andy,

I leave the piston clearance up to my machinist. I think he sets the piston up to 3-4/1000 depending on the particular piston, cast or forged.

I have only had one head to repair for the center journal and it was due to low oil. Another engine I worked on last year that did drop a seat had been run VERY hot and was no longer serviceable as it was fractured, cracked everywhere. One thing my machinist told me about when a center journal gets damaged due to low oil is that since it is low on oil it gets real hot and the area above the combustion chamber expands from the heat and ends up squeezing the cam thus the journal galling. Lack of oil and tighter or no clearance and there you have it.

If you have and concern with your head I would suggest that you send it out for inspection. Of course I have been a customer at Engine Dynamics for a very long time and Mike will give you the straight deal. http://www.enginedynamics.com/

Steve
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87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project
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Old 01-26-2012, 05:32 PM   #112
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Thanks Steve for the advice. I will probably do that. Hate to chunk a good used head if it is worth fixing.

Thanks again for the advice.

Andy
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"The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter cannot be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles." - Jeff Cooper
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Old 01-26-2012, 06:23 PM   #113
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Hot Dam. 10,000 views.

Hope somebody has found this thread useful.
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BMW's
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79 R100s
91 R100gs

87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project
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Old 01-26-2012, 07:47 PM   #114
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Quote:
Originally Posted by mcma111 View Post
Hot Dam. 10,000 views.

Hope somebody has found this thread useful.
HELL YES IT"S USEFUL! It should be a sticky so it's always at the top of the thumpers forum. Thanks again!

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Old 01-31-2012, 01:42 AM   #115
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Quote:
Originally Posted by mcma111 View Post
Hot Dam. 10,000 views.

Hope somebody has found this thread useful.
Congratulations on reaching 10,000 views of this thread, Steve. I certainly referred to this thread many times during the recent, top end rebuild of my XR650L engine. Once again, thank you for documenting your work with the excellent photographs, tips, and explanations. I'm pleased to report my bike is running very well after its top end rebuild.

I have recently begun to wonder how the auto decompression system works in the XR650L engine. How is the small, spring-loaded nub of the automatic decompression system able to open the right exhaust valve? Also, why does this automatic decompression occur when starting the engine, yet does not occur after the engine is running?

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Old 01-31-2012, 08:12 AM   #116
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Thanks very much for this. Is it close enough to a XL600LMF to be used? If not, can you do one for the XL? Pretty please.
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Old 01-31-2012, 10:51 PM   #117
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Thanks to Walterxr650L, I found the following information on pages 9-7 and 9-8 of the new Honda Common Service Manual.



This information is not available on the old version of the Honda Common Service Manual.

I now understand how the auto decompression system works! The auto decompression plunger, part #7 in the drawing below, acts to stop the reverse decompression cam from rotating too far clockwise while the engine is running.



Here's a photograph of the decompression plunger, posted earlier in this thread by Steve, McMa111.



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Old 01-31-2012, 10:54 PM   #118
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I found this nice photograph of a stock camshaft posted by Cobia235.



Both decompression cams remain laterally fixed in place. Centrifugal force rotates both decompression cams either into, or out of operation when crankshaft rpms increase after the engine turns over.

It does appear both of these decompression cams might fall off the end of the camshaft if it is tilted with the cam sprocket collar removed.

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Old 03-05-2012, 12:11 PM   #119
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Hi Steve

I have a question about the cam sprocket timing marks. I was not able to get the marks aligned perfectly with the top of the head as you show in post 3. The left side was about .030 below the deck. Based on the size of the teeth on the sprocket, we thought we were good. What do you think? As always, I appreciate your help.

Joe
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Old 03-05-2012, 12:51 PM   #120
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Quote:
Originally Posted by opjocephus View Post
I have a question about the cam sprocket timing marks. I was not able to get the marks aligned perfectly with the top of the head as you show in post 3. The left side was about .030 below the deck. Based on the size of the teeth on the sprocket, we thought we were good. What do you think? As always, I appreciate your help.

Joe

If you can't get the cam gear to align by moving the gear one tooth one way or the other this is the tell tale sign that your cam chain has stretched.

This is something I try to remember to do when I tear down a bike. Put the engine at TDC (Edit: On the compression stroke) so the tension is off of the cam lobes and then once the rocker cover has been removed to check the cam gear timing marks. If the marks line up the chain goes back in. If off, mis-aligned then it's new cam chain time.
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BMW's
58 R26
79 R100s
91 R100gs

87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project

mcma111 screwed with this post 03-05-2012 at 03:58 PM
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