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Small Air Cooled Gasoline Engines

H35 Excessive Valve Clearance Issue


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  #1  
Old 07-27-2010, 10:38:36 AM
Mailman Mailman is offline
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Default H35 Excessive Valve Clearance Issue

Hello all,
I have a HT35 aspera motor which is pretty much the same as a H35 Tecumseh. I am rebuilding it and with new valves installed, the valve clearances are .014 and .028 for intake and exhaust, repectively.
I know the clearances should be .004 and .008 as per spec and I know to grind the valve stems when the valve clearances are too tight but how do you remove excessive clearance?

Can I get longer lifters? Do I need to weld a little bit on to lengthen a valve or lifter?

Any help would be appreciated.

Mailman
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Old 07-27-2010, 01:11:14 PM
Ironsides Ironsides is offline
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Default Re: H35 Excessive Valve Clearance Issue

Mailman,you don't make it clear if you have ground the valves in yet.I was amazed when I fitted new valves measured them,(unground) then ground them in how much difference it made.If you have already ground them then you may have to keep grinding.If your engine has loose cap followers you can place stainless steel discs inside the cap to close the gap up,(put a bit of grease in them to hold them in place as you assemble).Keep cranking,Norm
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Old 07-27-2010, 01:59:25 PM
Mailman Mailman is offline
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Default Re: H35 Excessive Valve Clearance Issue

Sorry about that. I have not ground the valves in yet and there is excessive clearance. The gap is too large and grinding will just make the matter worse. I need to make the valves or lifters longer.
There are caps that I know of. The lifters and valves are 1 piece units.
I appreciate your help. I feel like I am stuck in a round room looking for the corner.

Mailman
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Old 07-27-2010, 02:01:31 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: H35 Excessive Valve Clearance Issue

.010 seems an excessive amount of distance to try to recover by lapping in. Sounds like either the new valves are wrong, or perhaps the lifters are severly worn. If you have the engine apart, check the lifter faces, where they meet the camshaft. They should be dead flat. If they are 'cupped', check the cam as well for wear.
Andrew
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Old 07-27-2010, 02:12:03 PM
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OTTO-Sawyer OTTO-Sawyer is offline
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Default Re: H35 Excessive Valve Clearance Issue

Quote:
Originally Posted by Mailman View Post
... I have not ground the valves in yet and there is excessive clearance. The gap is too large and grinding will just make the matter worse....
Mailman
Grinding the stems would make the clearance problem worse.... Grinding the valve heads or the seats will make the valve set deeper in them closing up the gap on the stem.

After you grind the valves, then you check the clearance and grind the stems to fit if needed.
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Old 07-27-2010, 02:38:15 PM
Mailman Mailman is offline
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Default Re: H35 Excessive Valve Clearance Issue

I checked the faces on the lifters and they look fine. I have 2 cams and both give about the same reading.
I feel like I have to be forgetting some basic part that would take up the extra space. I would expect a neg. number for clearance with new valves until they were ground in.
Maybe the Aspera valves are a little longer?

Here is what is there and help find the flaw here.
Cam to lifter to valve. All 3 parts are solid and not adjustable. I may just need longer valves. Grrrrrrrr!

Thanks guys

---------- Post added at 11:38 AM ---------- Previous post was at 11:17 AM ----------

Quote:
Originally Posted by OTTO-Sawyer View Post
Grinding the stems would make the clearance problem worse.... Grinding the valve heads or the seats will make the valve set deeper in them closing up the gap on the stem.

After you grind the valves, then you check the clearance and grind the stems to fit if needed.
OK.
Is it normal to grind the valve heads in on new valves? Or is this done in my case to close the gap?
I thought I could just drop in new valves, grind the stems to the correct clearance and I would be good to go.
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Old 07-27-2010, 03:00:12 PM
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John Newman Jr. John Newman Jr. is offline
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Default Re: H35 Excessive Valve Clearance Issue

It is SOP (Standard Operating Procedure) to grind new valves to mate with the seats. I would start with the most coarse compound available to get maximum metal removal since you seem to have excessive stem to lifter clearance. Check that gap frequently as you lap the valves in as it may close up quickly once you get the valve & seat matched. Finish up with fine compound for a good smooth surface.
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Old 07-27-2010, 03:19:43 PM
Mailman Mailman is offline
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Default Re: H35 Excessive Valve Clearance Issue

You think that will do the trick and remove .010 from the intake and .020 from the exhaust?
Thanks again for all the help. I knew I had to lap the valves to help them seat but I didn't think I would be removing that much material.
Have you heard of this much clearance before on good parts?
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Old 07-27-2010, 03:33:46 PM
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Default Re: H35 Excessive Valve Clearance Issue

Cams and lifters wear too, even more so if they weren't broken in properly at a higher RPM so they get more oil thrown on them while breaking in. IF the engine never had a valve job done on it and the seats have very little wear on them, it's possible the excessive clearance with the new valves is due to cam/lifter wear, but the new valves may also have been made with excess clearance figuring the gap would close when the seats are ground.
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Old 07-27-2010, 03:34:33 PM
Roland Hayes Roland Hayes is offline
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Default Re: H35 Excessive Valve Clearance Issue

Hi, I recently restored an old but virtually unused Kohler 3MM65 dual voltage generating set, the engine is a Kohler K181EP. After completing the work I was dissapointed with the level of tappety noise from the very low hour engine, it spoilt the job really as I had gone to some length to make the machine quiet by fitting an effective silencer to the engine rather than the little pepper pot fitted as the standard silencer. Checking the valve lash clearances they were within the upper range specified in the service manual, that being 0.006"-.008" inlet and 0.017" - 0.019" exhaust. On dismantling the engine sufficiently to see the valve motion as I turned the crank, I was surprised to see that with the clearances on the wide side of correct there was no cam silencing ramp evident, the valves lifting straight off the seats and falling back without any gradual initial acceleration/deceleration of the valve off the seat, further checks revealed that those silencing ramps are there but only come into play at considerably smaller tappet clearances than mine. I put the valves up in my lathe and machined the seat area a little at a time using a very sharp carbide tool until each valve had been sunk into the block so as to reduce the lash clearance enough so that I could see gradual initial acc. and decel. of the valve off its respective seat, like this I came to a tappet clearance of 0.005" inlet and 0.010" exhaust. On running the engine after reassembly the change in the character of the engine is noticable, a much nicer quieter sound and sweeter running. My guess is that Kohler's require the engine to run without service to the valve gear for long periods and built in extra lash on the valves to guard against wear on the seats reducing that lash to to the point of causing the valves to overheat and burn. If you are prepared to periodically check the lash clearances then there is no need to live with the unneccesary noise that this exessive clearance brings about, my advice is to close them up, but keep an eye on your cam silencing ramps and try not to overdo it, if you go too far its easy enough to stone a few thou from the end of the stem and restore some clearance. Hope this is of interest to you, warm regards Roland

Last edited by Roland Hayes; 07-27-2010 at 04:56:56 PM. Reason: spelling
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Old 07-27-2010, 04:48:12 PM
Roland Hayes Roland Hayes is offline
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Default Re: H35 Excessive Valve Clearance Issue

Pictures of the Kohler 3MM65 genset that I mentioned in my previous post, I wired the exiter to give electric starting and battery charging while I was at it. These are great sets, just about as bulletproof as you can get. Rgds, Roland
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Old 07-27-2010, 05:44:38 PM
Ed Radtke Ed Radtke is offline
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Default Re: H35 Excessive Valve Clearance Issue

if your instaling new valves then I have to suspect that the seat in the block will need to be touched with a stone to true them up.this combined with the followup lapping should get you where you need to be to make your tappet adjustment.
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Old 07-27-2010, 08:41:23 PM
xplor xplor is offline
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Default Re: H35 Excessive Valve Clearance Issue

Fitting valves was common practice on flat head Fords.
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Old 07-27-2010, 10:40:51 PM
Mailman Mailman is offline
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Default Re: H35 Excessive Valve Clearance Issue

Thanks Guys. I will try your suggestions and let you know how it turns it.
I truly appreciate them all.

Mailman
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Old 07-28-2010, 01:40:45 AM
J Sorensen J Sorensen is offline
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Default Re: H35 Excessive Valve Clearance Issue

Just a thought. Are you checking the valve clearance with the side cover in place? I had a lot of students forget to do this over the years.
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Old 07-28-2010, 11:08:33 AM
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Default Re: H35 Excessive Valve Clearance Issue

Excellent Point, Teach! I did not have the cover on. I put it on and it took up the clearance issue on the exhaust but I still have excessive clearance on the intake.
I actually have my original numbers reversed. The intake had the .028 clearance and the exhaust had the .014.
Now the exhaust is neg. so I can just grind the stem to fit. Yeah!
The intake is about .026 now. I have not lapped that valve yet. I will lap it and report back.

Does this mean I fail the course?
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Old 07-29-2010, 08:04:27 PM
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Default Re: H35 Excessive Valve Clearance Issue

Well, I lapped a little only to find out that there was no way that was going to take up all the slack. Some suggested to cut the valve seat to lower the valve.
I tried to swap the lifters but there was only .001" difference so no big gain there but it was worth a try.
Since the valve was good and the seat was good, I thought it was a little odd to grind on it so I had a little metal welded on to the lifter to lengthen it. I then ground that down to fit.
Everything is in spec now.:smile:

Thank you,

Mailman
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