Topic: Engine Flushing/ Oil Change for a CB750

[fendersrule]

This really seems like a rock solid procedure that I intend to follow:

http://forums.sohc4.net/index.php?topic=8237.msg76179#msg76179

But when I was in NAPA today, I found a quart of "NAPA fast flush". You're suppose to add it to pre existing oil, run the engine for 5 minutes, and then drain.

I was wondering if these products are worth it? My bike as 12,000 miles (from the PO). Not sure on the maintenance, so thought this could be interesting to do.

My CB450 may be a better candidate as it's been stored for sure for 10 years.

Has anyone used Engine flush before, and is it worth it?

[flybox1]

Don't kick over the engine or hit the starter once you've drained the tank and pan, or the oil removed by doing this  will not be there to lubricate the top end upon your next sartup ..... Which could be just enough to do damage until oil pressure builds back up and circulates.

[bollingball]

This really seems like a rock solid procedure that I intend to follow:

http://forums.sohc4.net/index.php?topic=8237.msg76179#msg76179

But when I was in NAPA today, I found a quart of "NAPA fast flush". You're suppose to add it to pre existing oil, run the engine for 5 minutes, and then drain.
I was wondering if these products are worth it? My bike as 12,000 miles (from the PO). Not sure on the maintenance, so thought this could be interesting to do.My CB450 may be a better candidate as it's been stored for sure for 10 years.Has anyone used Engine flush before, and is it worth it?

Does NAPA know you have a wet clutch??

[Kickstart]

IMHO - I would strongly recommend against using the flash flush.

It doesn't sound you have a specific issue you're trying to resolve.  Just concerned about oil sitting in the bikes for 10 years. 

I suspect you don't have a sludge problem (I don't believe our air-cooled bikes had problems with sludge), so I don't think you have anything you need to chemically de-grease.

I think it could cause more harm than good.

I recommend you just warm it up and change the oil.  And then do another oil change 200-500 miles later for good measure if you're still worried about the "stale" oil.
 

[Stev-o]

I wouldn't do it either. If your set on a flush, just give it two oil changes within a short running period. If it ain't broke...

[bjbuchanan]

If you are set on doing a flush I would go with seafoam. Proven worker there. Use half the bottle in the oil and then you can use a little in the tank later on if you feel like it

Put some in the oil tank, circulate the oil from getting it nice and hot and then change the oil. Don't leave seafoam in the tank it will act as a thinner so it isn't meant for long term use

[fendersrule]

Thanks guys ill go without a flushing.

[bjatwood]

Your answer was given, Seafoam. I use it once a year before a oil change. Add half a can, run it for 10 minutes and let it drain all night long. Works GREAT!!!!

[fendersrule]

I put about 15 miles on my bike since I've bought it off eBay.

Don't know the previous history behind it. 12,000 miles. Oil looks clear. Carbs were not gunked up. However, rear axle was stuck, front sprocket bolt was loose, and chain/sprockets were worn. And the rear tire had many cracks. Blinkers weren't working reliably.

It probably was stored for some time. Compression is low (120ish), but it starts, idles, and drives very nice. 

In not sure if I should flush the oil now, or put on some more miles first.

[lucky]

It is not a car engine.
Do NOT flush the engine!

Just change the oil and filter unless you want to possibly ruin the bearings. Wash junk out of the oil tank and into your engine.

[Deltarider]

Personally I don't understand this flushdesire at all. Motoroil by nature is a great dirtcollector itself. What more do you want?

[fendersrule]

How do you guys feel about putting 1 OZ of Marvel Mystery Oil in the oil now, then running it for a few days, and then changing the oil with a fresh filter?

[Stev-o]

I see no harm but a waste of time and money in my opinion.
Do you have reason to believe the motor was abused or sat outdoors?

[fendersrule]

I don't but the compression numbers aren't striking, either. I don't know if it sat for awhile prior to the PO? It runs great. But there's always a chance it can run "better"? That's why we're motor heads!

I've ONLY read positive things about MMO. If you Google it, you'll see cases where it actually raised compression for some (even after 500 miles), quieted some things down. I don't expect to do anything significant, but it doesn't hurt try since I got a bottle of it out here on the shelf. I also put Seafoam in every motorcycle tank. I have friends that swear by it. Seafoam is also an acclaimed product.

Anyhow, I would expect anything I've bought sight-unseen to have to do a good thorough cleanup, unless I'm causing harm.

After all, I'm going to be on the road consistently with it in 2 weeks. My first riding experience will be on a '78 CB750.

btw, pulling that CB450 motor at the end of March. I've always got a bike to work on now.

[Stev-o]

What type tester are you using to get your comp numbers? If it is an automotive type, the readings are not accurate for motorcycle engines.  More importantly, are your numbers within 10%?
I don't understand it, but it has been documented that the comp numbers will come up after a few hours of running time. 
Get that bike on the road!   Still cold up there, isn't it?

[fendersrule]

I've never heard that motorcycles don't give accurate numbers with regular compression testers. I'm using a push-type. Numbers are within 10% on both the CB450 and CB750. CB450 is nailing 131-133 PSI after a valve adjustment. 150 PSI is stated the minimum by the experts. CB750 is doing a little better. I'm going to check the compression on it again in the future. I got about 115-120 on the CB750, but I don't believe my dad had the choke open, nor do I remember it being on a warm engine, nor do I remember holding the throttle open. SOHCs can run great at low compression. DOHCs cannot.

Starting to approaches 50s here.

Tank and side covers go to the paint shop next week.

A battery strap came in for the CB750, but I don't understand how to install it. The notches on the bike are faced upward, and not downward. So the strap can easily sling out.

[70CB750]

The compression may improve with regular riding, it improved for me once I got on the road - instead just going in circles in the back yard during the pre-tag days.

However, as was said, if the reading is withing 10% across all four and the bike runs good, forget about it and just ride the heck out of it.

[Kickstart]

I've never heard that motorcycles don't give accurate numbers with regular compression testers...

The concept is the cylinders on our engines are smaller than the average car cylinder, so the volume within the long hose of the typical consumer grade car/truck compression tester has a more significant impact to the measurement.  I believe motorcycle dealers/mechanics have special compression testers (presumably the ID of the extension hose is smaller and/or the check valve is closer to the open end of the hose) - at least this is what I've heard.

...A battery strap came in for the CB750, but I don't understand how to install it. The notches on the bike are faced upward, and not downward. So the strap can easily sling out.

This doesn't sound right: the notches on the battery holder facing upward.  Can you take a picture of what you're seeing?

[fendersrule]

I'll take a picture of the battery strap later. I've about given up on it, and all I've managed to do is scratch my freshly powder coated tray.

I'll look into a motorcycle compression tester. Thanks for the heads up.

ALSO, found out that Marvel Mystery Oil is NOT recommended to come in contact with your engine oil, unless approved by the manufacturer. This is probably due to the wet clutch system. Seafoam is probably OK, though I haven't confirmed.

[bjatwood]

Seafoam is just fine for wet clutches. Have used it once a year since the birth of Bugs Bunny! 

[MCRider]

I'll take a picture of the battery strap later. I've about given up on it, and all I've managed to do is scratch my freshly powder coated tray.

I'll look into a motorcycle compression tester. Thanks for the heads up.

ALSO, found out that Marvel Mystery Oil is NOT recommended to come in contact with your engine oil, unless approved by the manufacturer. This is probably due to the wet clutch system. Seafoam is probably OK, though I haven't confirmed.

Confirmed by who? Inquiring minds...   

"Unless approved..." sounds like a CYA cop out statement. MMO recommends up 25% MMO/Oil ratio. Seafoam is something simillar, its on the can and on their website.

[fendersrule]

Take a look at these links:

http://www.marvelmysteryoil.com/index.php/forums/viewthread/311/#699

MMO representatives from the links listed in the link ( said that they do not recommend it unless the manufacter has approved of it. I'd say that's a confirmation that you shouldn't use MMO in your motorcycle oil unless Honda gave it a stamp of approval.

It looks like Seafoam however, can be used safely with your oil:

https://groups.google.com/forum/?fromgroups=#!topic/nighthawk_lovers/0SBJL9WJDHQ

[MCRider]

Take a look at these links:

http://www.marvelmysteryoil.com/index.php/forums/viewthread/311/#699

MMO representatives from the links listed in the link ( said that they do not recommend it unless the manufacter has approved of it. I'd say that's a confirmation that you shouldn't use MMO in your motorcycle oil unless Honda gave it a stamp of approval.

It looks like Seafoam however, can be used safely with your oil:

https://groups.google.com/forum/?fromgroups=#!topic/nighthawk_lovers/0SBJL9WJDHQ

Thanks. I'd say you're right. re: MMO and Seafoam. I do/have used Seafoam in various motorcycles, no obvious problem.

[Mace]

What would people recommend using to flush a dismantled engine? One which has obvious unwanted stuff in the crankcase. Diesel?

[PeWe]

Why flush a CB750?  Toyota, VW, Audi have their oil sludge histories. Car engines with turbos. I have never seen much dirt inside my CB750 when taking it apart (except for chain tensioner rubber and broken clutch parts. Drain the oil, remove filter and the oil pan and clear the mesh before oil pump to ensure good oil flow. Disconnect the oil tank and clean it and hoses with proper detergent.  New oil filter and oil.