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Discussion Starter · #1 ·
So a little back ground: I have been dealing with burning oil for nearly 6 months now. I did a compression test 3-4 weeks ago. I tested with the engine hot and the throttle open. I did not remove the air filter. I had removed the mufflers prior to this but retained the stock power chamber and headers. I repeated the test 3 times on each cylinder and got 145 PSI in each cylinder. I did not add any oil and retest. Obviously 145 is well below 185 +/- 15PSI. I suspect its the rings and I am in the process of gather parts or a full rebuild.

But here is my question. Why would I burn more oil withe the mufflers on than with them off?

Before I removed the mufflers I was pretty constantly blowing a cloud of bluish gray smoke out one or both of the pipes (usually the left, but it would switch and stop too). With the pipes installed my plugs looked sooty and the left side plug always had some wet oil on it. During this time I had to keep a pint of oil with me and constantly keep an eye on the oil. I do not have an accurate way to keep track of my distance, but I estimate I am riding between 100-200 miles a week and I was burning 1/2-1 pint every week.

I should note here that I am using NGK DPR8EA-9 (regapped to .025) plugs, (virtually the same as the DR8ES, the only difference it that the DPR is a projector tip, plug reach and heat range and resistance are all the same between the two). The machine is otherwise stock, air box,carbs, jetting (I think, it's been two years and I didn't write down the jet sizes) and has been kept up on maintenance and adjustment of valve lash, balance chain and cam chain. Oil was changed 3-4 months ago (its due again).

After I removed the mufflers I noticed that there was substantially less smoke coming out the pipes and oil consumption dropped drastically. It dropped so much that I stopped carrying oil with me because I was no longer afraid of burning it all up. Removing the mufflers leaned out the bike. I installed a new set of plugs when I took the pipes off. After a few days I pulled and checked the plugs and the right plug looked pretty lean while the left plug was a golden brown/tan, I would say it looked sort of rich but there was a lot less wet oil on the threads.

Yesterday I put the pipes back on to save my hearing and to remount my center stand. I immediately noticed a cloud of smoke rolling off the back of the bike when I stooped at a light and it was still happening when I got off the freeway.

I don't have the cam specs in front of me but I am thinking that there must be a good amount of valve overlap (anyone know the LSA off the top?) and that with the mufflers on I am getting more blow by because of the back pressure. Does that make sense? I can't think of any other reason my oil consumption would be directly related the mufflers.

I am going to try and keep accurate measure of the oil and miles this week and write it down. I may remove the pipes again to get a comparison of consumption. It would be interesting too to redo the compression test with the air filter out, then do the test both with the pipes and without.

Am I on the right track here? Do you guys have any ideas?
 

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Oil consumption can come from a variety of areas (rings, valve seals, head gasket, etc).. compression tests will only give you the "health" of the compression cylinder space.. not much more..
Do a leak down test, pretty simple, at TDC and DBC.. if there is a deficiency in that cylinder this test will help locate and identify where and possibly what it is..
Just do a few simple things before you introduce compressed air into that motor.. have the motor in high gear and either have the front wheel against a wall or atleast locked down..
Keep us posted
 

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Does the engine have a breather that could be clogged? I think they have a fair amount of overlap. Plugged exhausts sound reasonable. Maybe LDR will have an idea. At any rate if the compression numbers aren't within spec, it'll be hard ever tune it up right.
 

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Valve open duration is in the 330 degree area so there's a lot of overlap.
Oil smoke with the mufflers on would be due to oil accumulation and slower burn off, shorter mufflers or none would allow the oil to blow out rather than pool and burn.
Compression and leak down tests are pointless for this since they are testing the valve seating and compression rings, not the oil control ring or valve seals.
Also running rich means there's excess fuel in the combustion chamber which will dilute the oil on the cylinder walls allowing more to flow past the oil control ring.
Given that you're at 145 compression I'd venture a guess that the oil control rings have seen the end of their days or possibly be sticking in the ring lands of the pistons.
So do the top end including valve seals. Use Honda rings, they're still available in Std. and use Viton valve seals, non-Honda. You can find them on eBay. Get the cylinder and pistons measured before ordering parts, odds are that Std. will be fine since cylinder wall and piston wear are usually in spec. You might want to do a valve job at this same time, the valves cannot be resurfaced, replacement only.
 

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Discussion Starter · #5 ·
Rob- I don't have the equipment for a leak down test. My compression tester is a cheapo one.

Lefty- My breather is free of obstruction.

LDR- Are the OE rings worth the cost over cruzinimage_co? Viton valve seals are on my list. My thought is on the rebuild is that I might as well rebuild the bottom end at the same time. I already have the flywheel puller and clutch tool but jesus is it expensive to replace everything in one of these engines.

I suppose what I really ought to do is throw in my spare 450 engine and start collecting parts.
 

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The rings from Cruzin Image should be fine, no reports of bad when people have used them with his pistons. I point people towards the OEM because they are a known quality. There's so much cheap junk to be found on eBay.
Yes, it is expensive to go through one of these engines. They all seem to have suffered from neglect rather than poor engineering and production. Good news is that once done and maintained you'll be trouble free in that area for years to come.
 

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Discussion Starter · #7 ·
Any source for oversized pistons? I've seen them for the 400's but the 450.
 

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I don't have a source for those, you really need to get the cylinders and pistons measured first. I know that most of the 400's stay in spec at 50K miles plus.
 

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Discussion Starter · #9 ·
What's that usually run at a machine shop? I've got a parts engine who's pistons and cylinders look good. I was planning to start an engine build thread once I get started so stay tuned for a lot more questions. I read your engine build thread, would you recommend the oiling mod you did?
 

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The oiling mod for the cylinder head only applies to the 400 engine, the 450 is already as good as it gets.
I don't know any good machine shops in the Bay Area anymore, been gone too long. Call a couple of MC dealership service dept's and see who they use. Just cleaning and measuring shouldn't be much
 
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