GS450 Low Compression after rebuild

[JRHemmen]

I just finished putting all the valves back in. When I went to put the head back on, I realized that I hadn't put the 2 little dowels back in the first time, maybe that was part of the problem. I took pictures of the cylinders as well.

[londonboards]

I don't want to be a miserable bastard or stop anyone from having any fun but it seems to me that your knowledge of bike engines and basic mechanics at this point in time is so lacking that you should really stop this project before too much more damage is done. I really don't mean to be rude but honestly is the best policy here.

This is what I recommend. Spend some time reading up about valve trains, springs, pistons, engines and general bike stuff. Start here: http://members.dslextreme.com/users/bikecliff/. There are all kinds of articles there that will help you with valve lapping and the like.

Try to find a GSR member near to you who is willing to spend a couple of hours with you looking into your engine. Honestly, stuff like cam chain timing and the like are hard enough to understand for guys who have been ripping these engines apart for over 20 years.

It is so difficult for any of us to help you on a forum like this when we know nothing about your level of experience with these things. It just seems that from what you have written that you are in danger of making things worse because you really don't know what you are doing.

The 2 most obvious ones to me are; you need to hold the throttle wide open when you are doing compression testing (it will tell you this if you read anything about compression testing or look at any YouTube vid) and secondly you left the collets out when you re-assembled the valves and springs. Without the collets ("little dowels" as you call them) the valve will not close at all. I'm guessing you might just get a 40psi reading even if all your valves were stuck open.

The other thing is that cylinder wall does not look good to me. You need to get this checked physically by someone that knows.

I just think you ought to get someone over to take and look at your motor whilst it's apart. Get some help from someone. There is only so much we can do by remote from here.

I want you to get that bike back on the road and for it to be safe a reliable and right now I don't think we are going the right way about it.

[JRHemmen]

I don't want to be a miserable bastard or stop anyone from having any fun but it seems to me that your knowledge of bike engines and basic mechanics at this point in time is so lacking that you should really stop this project before too much more damage is done. I really don't mean to be rude but honestly is the best policy here.

This is what I recommend. Spend some time reading up about valve trains, springs, pistons, engines and general bike stuff. Start here: http://members.dslextreme.com/users/bikecliff/. There are all kinds of articles there that will help you with valve lapping and the like.

Try to find a GSR member near to you who is willing to spend a couple of hours with you looking into your engine. Honestly, stuff like cam chain timing and the like are hard enough to understand for guys who have been ripping these engines apart for over 20 years.

It is so difficult for any of us to help you on a forum like this when we know nothing about your level of experience with these things. It just seems that from what you have written that you are in danger of making things worse because you really don't know what you are doing.

The 2 most obvious ones to me are; you need to hold the throttle wide open when you are doing compression testing (it will tell you this if you read anything about compression testing or look at any YouTube vid) and secondly you left the collets out when you re-assembled the valves and springs. Without the collets ("little dowels" as you call them) the valve will not close at all. I'm guessing you might just get a 40psi reading even if all your valves were stuck open.

The other thing is that cylinder wall does not look good to me. You need to get this checked physically by someone that knows.

I just think you ought to get someone over to take and look at your motor whilst it's apart. Get some help from someone. There is only so much we can do by remote from here.

I want you to get that bike back on the road and for it to be safe a reliable and right now I don't think we are going the right way about it.

I appreciate the concern. I am new to mechanics, and I planned for this bike to be how I learn. I wasn't referring to the keepers, those are all in place correctly. I meant the hollow tubes that go between the head and the jugs, approx. 1cm in diameter and 2cm long.

I admit I didn't do any reading on compression testing, I went by what the worker at autozone told me, which included nothing about the throttle. I've certainly been anxious about getting the bike running, but I'm trying and will continue to try to keep that from interfering with the quality of my work. I extensively read through the bikecliff site as well.

[gs45082]

I might hesitate to go as far as Richard, but stepping back and doing a little reading before tearing into a motor for a second time might pay some serious dividends in saving you time and money, not to mention reducing potential for damaging your motor. We all want you to have a safe, fun bike; and as a fellow 450 owner I can tell you it's worth the frustration when it all comes together and you're tearing down some good roads. You have an amazing little machine waiting on the other side of all this work.

First thing first, do you have a manual? I mean an actual paper book. YouTube and the forums certainly have their place you're not getting very far without a manual. I got this one off amazon and it's been great: http://www.amazon.com/gp/product/089...ilpage_o05_s00

As indicated, your bores look quite rough. But not seeing them in person makes this a tricky call. If you drag your fingernail nail across any of the gouges, do you feel it hanging? With all the other unknowns flying around, I'd probably just put it all back together (correctly this time!!!), and see what your compression reads. And get a wet reading too by squirting a little oil in the plug holes, if compression increases by a large margin (15-20 psi increase??) then yes you need a ring job. Buuuuut even in that case, you probably have enough compression to get her running, at least to see if everything else is in good enough shape to justify the ring job.

[JRHemmen]

I just ordered that manual, thanks. I looked over the cylinders, and had someone else look over them, and they both seemed fine. I think it's just some kind of stain in the picture, because they feel totally smooth when running a fingernail over them.

[tkent02]

I took pictures of the cylinders as well.

These cylinders are wasted from sitting with water in the bores, that's rust in a nice straight line because thats where the piston rings were. Rings are probably toast too. Easy fix, replace the cylinder, pistons and rings with Ebay stuff. However, that same water also likely ruined things down inside the engine as well. You probably have rust on all kinds of stuff down inside there. I bet if you were to pull the pan off the bottom of the engine that water would still be in there. Take a look.

[JRHemmen]

These cylinders are wasted from sitting with water in the bores, that's rust in a nice straight line because thats where the piston rings were. Rings are probably toast too. Easy fix, replace the cylinder, pistons and rings with Ebay stuff. However, that same water also likely ruined things down inside the engine as well. You probably have rust on all kinds of stuff down inside there. I bet if you were to pull the pan off the bottom of the engine that water would still be in there. Take a look.

I have pictures of the pan in my build thread, I didn't see rust on anything when I had it all apart. How would water have gotten in there, condensation? The bike was stored inside at the POs, and at my home as well.

[tkent02]

Maybe some previous owner left it outside with a spark plug out or maybe with the carburetors off. Could have been a long time ago. Not sure, but I've seen it before, it's rust.

[JRHemmen]

Do these pistons and rings look acceptable? Also, is there any way I could clean the cylinders out without buying new ones?

https://www.ebay.com/ulk/itm/400656792028

[gearhead13]

The best way would be to buy new rings and hone the cylinders. I doubt there is anything wrong with the pistons, but the rings are an unknown. Depending on the mileage on the engine, maybe just a light hone job with the current rings would suffice.

[JRHemmen]

Okay, I wasn't sure if honing would suffice. How do I go about testing the rings without putting it all back together for a compression test?

[Nessism]

Heres the exhaust valve from the cylinder putting out 40 PSI. My guess is that my timing was off, because the valves didn't look that bad and I have a brand new head gasket.

John, I'll post a picture of the cylinder walls in a bit, I'm headed out to get the spring compressor now.

The valve seat is loaded with carbon. You will never get good compression on this hole until that situation is rectified.

Using power tools to lap the valves is not advised since it will cause a ridge to form in the valve.

Most machine shops will face the valve and kiss the tip for just a few bucks. Money well spent.

One other thing to do is measure the valve seat contact patch width. The OEM spec is something like 1.2mm max, but 1.8mm should be okay for a used bike. If the seat width is wider than this I'd get the seats cut though.

[tkent02]

Using power tools to lap the valves is not advised since it will cause a ridge to form in the valve.

A few seconds with a slow speed drill pulling on the valve with a rubber hose won't ridge anything. Did it last night on an XL500 head, the valves are sealing tightly now.

[JRHemmen]

Would the bike theoretically be able to run before I hone the cylinders and replace the rings? I'm wondering if it's something I could put off until I take the engine out again to paint the frame, or if it needs done now.

[gearhead13]

Okay, I wasn't sure if honing would suffice. How do I go about testing the rings without putting it all back together for a compression test?

You can check ring end gap by putting a ring in the cylinder and measuring the end gap with feeler gauges the spec for end gaps are in the manual. As the rings wear, the end gap widens, so this would give you an idea of the condition of the rings.