MrRover75

Hi all,

As I am going to take my OS .70 Surpass apart, I want to ask for advice regarding the need for cleaning, checking and potential laping of the cylinder head valves? Can the valves of these engines be lapped like a conventional car engine or should nothing be done or in other ways?

Thanks for your great answers

706jim

Shouldn't require lapping but f you do this operation use a gentle abrasive. Maybe toothpaste as the seats ae not hard like in a car engine.

HansenTsang

I like to check for leaks first before deciding if anything needs to be done. Take the head apart. Take off the valve spring. Turn the cylinder head upside down and keep the valves in place. Gently push the valves in place. Then put some alcohol on the combustion chamber. Look to see if any of the alcohol is leaking out. If the valves are holding back the alcohol you are good to go.

Ok I am not talking first hand about an OS 70 Surpass. I did this method on a Saito FA72.

Mine didn't leak. However just for grins I put a bit of Flitz metal polish on the valves and spun it with a fuel tube slipped over the valve stems. It did shine up the edge of the valves nicely.

MrRover75

A bit of metal polish seems reasonable if they are leaking Thanks for the tip.

MrRover75

Hi all,

Just coming back to this old thread... I have 2 X OS 70Surpass. The first one was taken apart right after I posted this thread. It got a good clean up, new bearings and I lapped/cleaned the valves slightly with metal polish as advised above. Worked like a threat and had good compression and nice running after the rebuild. This engine has had many flights after that and perform well and seems reliable

I am now going through the same operation with my number #2 70Surpass these days. New bearings in and bottom end OK. But I am struggling to get the valves tight. Gave them a clean up and a round with the metal polish. Can definitely see that this engine has been through more running than my #1. Bought it used many years ago, so have no clue about its history. After assembly, I can clearly hear a "hiss" of air going through the valves during turn over, most out of the inlet. Most of the compression is leaking out during a slow "flip" of the propeller. Its not like when I am doing the same on #1 and my other Saitos. So, my conclusion is that I might have a valve issue on this.
I have read through several threads/posts on this forum and it seems that the main advice is to stay away from conventional lapping/grinding compound on these engines and only do some light work with metal polish. If this don`t work, what to do? I am tempted to take the cylinder head of and do another round with metal polish. Not sureit might help?
What to look for and what to do?
Your advice would be greatly appreciated

the Wasp

My Feedback: (1)

I never saw the insides of the OS 70. but if both valves have the same size OD, they may be swapped. try swapping the valves to see if the leaking stops.
the valves in these engines are rather hard. I don't see metal polish hurting the valve's seat. but if that polish has grit in it, it could scratch the head's aluminum seat.

you can buy some very fine lapping compound. it's finer than what people use on auto valves. it's expensive but I don't see a problem using it on these engines as long as you don't overdo it. I mean really. other than trying a different valve what else are you going to do. you do not have the tool to make a new seat in the head. don't use much compound, just a little bit, and don't press hard at all. I used lapping compound on a Saito 91. it worked well on the intake valve, but the exhaust seat in the head was too messed up to fix. the hole that was cut for the seat was cut off center.
maybe someone will have a good idea for you.

Jim

1200SportsterRider

James, I did a little digging and the OS 70 FS and the OS FS 70 Ultimate each have .440" diameter intake and .410" diameter exhaust valves. Personally I never lap anything but I do chuck the valves up and clean them with steel wool. Gary sent me some valves a while back and they were so clean, but I don't know how he does it.

Propworn

My Feedback: (3)

You can order very fine lapping compound even super fine diamond compound. Check the valves that after lapping there is a witness mark from the compound around the whole face of the valve. If not you may have a bent valve. If there is too much play in the valve guide this can cause that hissing you hear. Bent valve you will need to replace it. Worn valve guides you will need to replace the head.
If its the guides and you still have compression on a fast flip and cannot find a new or good used head assembly you can try putting it back together and just running it the way it is. You may be pleasantly surprised how well and how much life there still is in it.

Jesse Open

Most people attempting to "lap" valves do far more harm than good. Lapping is not by any stretch a subsitute for proper cutting or machining.

Don't over-do it! You are pretty well limited to just cleaning the seat. This is not a substitute for proper machining. Use rather soft compounds not hard! A paste made with Comet Cleanser and water, used gently and briefly should suffice. Do not spin the valve. Instead use back and forth rotation, lifting the valve slightly and moving slighty between rotations. Even if you do not get a perfect seal, in most cases you will see the seating improve with some run time.
Again, avoid hard compounds and dont overdo it!

MrRover75

Hi all, and thank you for your feedback. As already stated, the diameter of the valves are different, so they are not swapped around. The cylinder head has a brass(?) insert for the valve seats. I dismantled the cylinder head and give the valves another round with some metal polish. No difference when re-assembled. I filled the inlet and exhaust port with some WD40 when the valves was back in, but could not see any leakage through the valves. Should maybe use some kind of alcohol instead? I am tempted to try some fine grinding compound as stated above, but think will give it a test run first and see how it runs. Are there any chance that the valves will close better after some running?

Not the best picture attached, but you can probably spot the difference in valve size and see the brass insert. The seats looks better than in the picture:

kmeyers

I have used used tooth paste myself to clean these up.

I do like working on the OS two piece head and cylinder more than the one piece Saito.

I have in mind a new project of converting a .90 OS or a .100 Saito from glow to gas.

Good luck with your "like new engines".

Propworn

My Feedback: (3)

I would clean what appears to be carbon from the valves and head first of all.

hellcat 1

I clean all the carbon off the valves. there are many ways to do this. Then make sure they are clean and dry of all lubrication. I glue a eraser end of a pencil to the valve face and lap it in with toothpaste. As has already been stated, do not spin the valve, just rotate it back and forth. Some toothpaste with baking power works good. You may have to glue the eraser on several times as they will sometimes break loose. After lapping, cut the eraser loose and clean the valve face well. This has worked well for me on several engines. Listen at the intake and exhaust port for a hiss when coming up on compression to check and see if you have a leak.

the Wasp

My Feedback: (1)

this is the tool you need to lap. among other things. I coated it with Titebond 3, and sanded it. Titebond is all I had.

jaka54

First check the valve seat and the surface on the valve! The surface should be uniform and not pitted. I have never seen a pitted valve seat or valve surface during my 48 years in this hobby.

Propworn

My Feedback: (3)

To lap the valves I use a pin vice on the valve stem and lightly pull the valve into the seat. This works well even for saito engines.

kmeyers

It also works well on Chevy's!

hellcat 1

Is that a rare earth magnet? should work pretty good. as stated earlier, a good pin vice will work although there isn't much of the valve to clamp down on. I have tried that also. I do have a old O.S. .90 with the valves in the back that the exhaust vale seat is pitted, but I was able to lap in in enough, and it still runs good. I have had it since 1988. Tons of hours on it.

Propworn

My Feedback: (3)

Pin vise might be kind of small. Lol

Jesse Open

Yes sir!
Lapping is best held as a last resort

Best underdone, too often overdone.

the Wasp

My Feedback: (1)

good idea there.

Jim

the Wasp

My Feedback: (1)

yes it is, my son had them. have had them some 10 years. just setting around.

Jim

hellcat 1

I have had 3 O.S. 91 Surpasses that the intake valve face wore down so bad that it would fit inside the seat and not seal. I ended up replacing the valve and the engines ran fine after. One clue that this is happening is the you have to constantly adjust the valve and you finally lose all compression. I have never had an exhaust valve do this though. I have had several bad cams on Saitos. The lifter seems to hammer the lobe and they get noisy You can see the cupped out place on the lobe. the only cure is a new cam.

Jesse Open

Never seen it done any other way
(On toy engines)
We didn't lap full size engines in the cylinder head shop. No need when the cutting and grinding are properly done.

MrRover75

Hi all,

Thanks for all advice. I got hold of some very fine honing compound. Seems a tad more course than the metal polish compound I have but finer than the valve lapping compound. I dismantled and gave it a try. Only did a gentle round with the valves. Put things together and exactly the same leak. Started the engine in a bench tester. Had to use the starter, no luck flipping it to start by hand. Did not get it to run reliable. It did 10500RPM with a 12x7 APC on it.
Back to square one. I will just throw it back into the box at the moment, using it for future spares to my #1. Maybe I will decide on a new try after some thinking...