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Old 04-14-2017, 03:27 PM   #1
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Sl350 cam bolt problems

Riding through Ennis yesterday looking for bluebonnets, the old SL350 gave up the ghost. Immediate shut down like turning a switch. Luckily a church parking lot was within rolling range on the two lane, no shoulder road I was riding at the time. We were 50 miles into the ride but luckily were a) with a trailer and b) real close to it. Initially we had talked about riding all the way down to Ennis.

In the parking lot it only took a couple kicks to realize the problem was catastrophic. No compression at all.

We trailered back home and all I did last night was order a gasket kit to get it on it's way.

This morning I started tearing into it early on Good Friday. I was 100% ready to pull the engine and I stepped back and eyeballed it and could see that the top plate covering the cam could be removed without taking the engine out and breaking my back.



And close inspection revealed the bolts holding the cam chain gear to the cam were sheared/missing. With a flashlight and reading glasses I found both bolts. Then I cussed the mechanic who did this and must not have used locktite AND new bolts. These bolts are the holy Grail of SL350/CB350s and that idiot re-used his old bolts instead of the two OEM new bolts he was hoarding. By now you much know I am that idiot previous mechanic but I swear I put locktite on them. Must have been oily or something and please, any suggestions appreciated on attaching them to torque specs and not having this catastrophic error.

I am betting I can do this without removing the engine. I did find and remove the two bolts and washed all the few shards down to the lower case to get picked up by the filter. There was a little pitting on one spot of the cam but I don't think it is related.

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Old 04-14-2017, 03:37 PM   #2
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Re: Sl350 cam bolt problems

I had a CB350 shut down like that on 35! Lucky it was a easy fix a head bolt backed out and grounded the plug and killed the motor. Coasted down the nearest off ramp,tightened the bolt and was off to the races again. Man that was like 1981 or 1982 in Waco.
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Old 04-14-2017, 03:44 PM   #3
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Re: Sl350 cam bolt problems

I35?
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Old 04-14-2017, 03:48 PM   #4
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Re: Sl350 cam bolt problems

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I35?
Yep sure was exciting.
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Old 04-14-2017, 05:55 PM   #5
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Re: Sl350 cam bolt problems

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I35?
Like Drew said, 1981 or '82. Back in those days, there were entire quarter-mile stretches without slowdowns, stop-gos, or incidents of road rage. Ah, the good old days...
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Old 04-14-2017, 04:11 PM   #6
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Re: Sl350 cam bolt problems

I just hope the cam didn't stop turning whilst it was holding a valve open or you will have to remove the head to replace a bent valve!! They are interference engines..

Gary
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Old 04-14-2017, 04:51 PM   #7
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Re: Sl350 cam bolt problems

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They are interference engines..
Gary
Yeah, this may be the first thing to check, because if the worst happened, your going to have to disassemble the top end and tightening the cam bolts won't seem so hard.
Take you spark plug out. Turn the cam lobes down so they are not lifting the cam followers. Remove your valve stem from your compression tester and screw the compression tester in the plug hole. Now take your compressed air line and put it to the tester hose. If you feel air coming out of the carb intake or the exhaust you have a valve that is not tight against the seat. NOT GOOD. depending on the amount, it could be just a leaky seat or if a lot it may be the fact that the valve kissed the piston, not in a good way.

Good luck, I have seen these break a chain and not touch, but it was at idle RPM so slow rotation. (not my rebuild)

Again Good Luck. I will go out in the garage and sacrifice some old part to the "manic mechanic spirit" for you.

Sam
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Old 04-14-2017, 08:31 PM   #8
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Re: Sl350 cam bolt problems

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Originally Posted by Thrasherg View Post
I just hope the cam didn't stop turning whilst it was holding a valve open or you will have to remove the head to replace a bent valve!! They are interference engines..

Gary
Actually it's a good bet that there is a valve dented and bent.

I also worry about the cam and if a portion of the bolt remains in the cam. From the picture I can see one bolt hole and it is clean. The bottom one remains un-inspected.

My thoughts right now are to take the rockers off and get the cam gear bolted on again. Reassemble and test compression.

Edit: I did not hear any metal to metal contact when the engine died.
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Last edited by SL350; 04-14-2017 at 08:34 PM.
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Old 04-14-2017, 06:31 PM   #9
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Re: Sl350 cam bolt problems

I don't mind doing an overhaul. It's getting the core in and out. But I have another engine if this one is toast.
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Old 04-14-2017, 08:47 PM   #10
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Re: Sl350 cam bolt problems

One more clue. If the valve is bent and staying open usually you will have a large valve lash change...Suddenly!

Hope you can save it.

Sam
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Old 04-14-2017, 09:40 PM   #11
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Re: Sl350 cam bolt problems

Very true! I had not thought about that.
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Old 04-15-2017, 12:12 PM   #12
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Re: Sl350 cam bolt problems

After another hour or two this morning I have the cam bearings off, the rockers, the cam and the cam gear out. I see damage to the cam but only slightly and likely not going to contact the rocker. The gear on the cam also has damage and I am looking through the big SL350 parts box (a Rubbermaid action packer completely full). It will likely be replaced and when I do, I am using alcohol to clean the bolt holes where the failure happened that caused this top end shakeup.

Before I do anything I am heading to the auto parts store for red locktite, NEW red locktite. Still don't know how the old bolts came out. Also need to find the two tiny bolts in the parts bin (last I looked, a set sold for $25 on eBay). If anyone Honda twin owner reads this later - do not use hardware store bolts.

And this job is going to wait for those gaskets anyways - the cam bearing were binded and destroyed the gasket.


Wish I knew if I had a bent valve before going further but until I have the cam back in and test compression, I just don't know. Since the valve rockers are removed I won't even be able to tell if they are widely different setting the lash.


Lots of you guys are out today - I can hear you.
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Old 04-15-2017, 09:29 PM   #13
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Re: Sl350 cam bolt problems

It's toast. With the cam out and no pressure on the valve springs, I got zero compression out of the right cylinder. Good on the left.

This is one that will drive me nuts. The engine was running great. I pulled it out the replace the cam chain tensioner. Now, the very problem I was trying to avoid, has wrecked the engine.

I can either repair this engine or use this one.
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Old 04-16-2017, 07:58 AM   #14
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Re: Sl350 cam bolt problems

Surely you can't scrap an engine because it has a bent valve!! It can't be very difficult to remove the engine, you might even be able to remove the head with the engine in the frame. If the engine is the original engine, I would be trying to keep it all together as it's worth more with the original engine. It can only be a 2 valve per cylinder engine, so likely only 1 valve is bent. You just need a new head gasket, I would even consider taking the head of the good engine and putting it on this engine, if it's the original engine. Of course, if this isn't the original engine, then I would just swap them over and be done with it. I don't know where you are located, but if it's any where near McKinney (just north of Dallas) you are more than welcome to bring it to me and we can swap them over in a couple of hours, or remove the head and fit the other (if you have a new head gasket).

Gary
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Old 04-16-2017, 12:04 PM   #15
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Re: Sl350 cam bolt problems

Well the original engine is the one not in the bike at this time. It was hemorrhaging metal shavings so I took it out in December.
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Old 04-17-2017, 10:34 AM   #16
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Re: Sl350 cam bolt problems

Quote:
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Well the original engine is the one not in the bike at this time. It was hemorrhaging metal shavings so I took it out in December.
If I have the choice between a known good engine with a bent valve (because the cam bolts broke) or an engine that was producing metal shavings, I would go the the bent valve motor every time!! Do you have any clue why the original motor was creating the shavings? What has failed internally? I would not be putting that engine back in without a complete dismantle to find the cause and asses what has been damaged by the filings!! Swapping heads or repairing your current head, sounds a much better option to me.. It looks like you are not too far away from me, so my offer still stands, if you want a hand, I am not a professional mechanic, but have built more than 20 engines and am very willing to help you if you bring the motor bike to my house, I have plenty of space and tools, get a new head gasket and we can swap heads, or we can take the old head off and get it fixed then put it back together afterwards.

Gary
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Old 04-17-2017, 09:32 AM   #17
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Re: Sl350 cam bolt problems

Have the bike/frame on its side on a piece of cardboard and let the engine out that way. Beats injuring your back wrestling it out of the frame. Hate to hear your having troubles with the 350.
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Old 04-17-2017, 11:16 AM   #18
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Re: Sl350 cam bolt problems

Thanks for the offer if I get to the point that I am stumped then I will send you a note. Agree on the engine choices.
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Old 05-01-2017, 08:30 PM   #19
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Re: Sl350 cam bolt problems

The engine is out, the replacement parts are here, and yes, it is a bent valve. One of the exhaust valves is open 1/8". Since I don't have a spring compressor or the knowledge to use one, I will take it to Plano to the Honda mower shop. THey have done excellent machine work for me in the past and charge little. It does help that I take in the head already removed from the engine.

The piston looks undamaged but I can see where the carbon was removed where the piston met the valve.
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Old 05-25-2017, 01:13 PM   #20
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Re: Sl350 cam bolt problems

Follow up: the old SL350 is back road ready. I will spare you the boring rebuild details - just the exceptions:

Putting the battery back in the ground connector broke off. Before crimping on a new one I found the copper wire on the ground was corroded about 3 inches. Repaired with a new terminal and soldered in about 4 inches of wire. This was going to be a problem and I was glad to find it in the garage.

After looking for an hour for the rear brake light switch I finally found it still on the bike but pushed out of the way to ease the engine in and out.

Plano Power Equipment (Andy) did the work. I took the head and a spare head and he removed a used valve from the spare, cleaned the head, replaced the bent valve, lapped all four and did it for $100. The engine is quieter now.

Rode it to get some gas and it appears road ready.

Fini.
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