Destroying valve guides .. Need Help

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.
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Destroying valve guides .. Need Help

Post by HoustonMule » Mon Mar 01, 2021 7:55 am

Helping friend with his 53 M38 engine replacement. Engine built by reputable shop. Installed rebuilt engine and after several hours of running a loud tapping started. Pulled engine and returned to shop only to find all valve guides in #1 and #2 cylinders had severe elongated wear. These were all new parts. Shop replaced guides and valves. Put engine back in. Ran fine for several hours then a Tick returned ... Pulled tappet inspection cover only to find #1exhaust guide worn and elongated. We used a high zinc break-in oil and prelubed engine prior to starting. Any thoughts on what is causing this valve guide issue??? We are stumped. Guides and valves were E-Loy brand.


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Re: Destroying valve guides .. Need Help

Post by Joe Gopan » Mon Mar 01, 2021 8:29 am

Sounds like your block may have worn Valve Tappet bores, a set of WO-115948 0.004" Valve Tappets may be required. Consult your M-38 Engine Ordnance Maintenance Manual TM9-1804A for the Valve Tappet Bore Specs.
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Re: Destroying valve guides .. Need Help

Post by W. Winget » Mon Mar 01, 2021 12:00 pm

Were the guides reamed to spec and the valve stems checked for size before running, or just assembled everything and ran her?
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Re: Destroying valve guides .. Need Help

Post by HoustonMule » Mon Mar 01, 2021 12:17 pm

Shop stated that reamed and sized to new valves then seats done.

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Re: Destroying valve guides .. Need Help

Post by Scrumps » Mon Mar 01, 2021 12:44 pm

Hi,

I had exactly this problem on my engine after my first rebuild.

It turned out that when I refitted the valves I failed to notice that the springs were not correctly seated on the machined surface around the guides. Nett result was that the valves didn’t go up and down concentric with the guides and caused wear.

The wear was so bad I ended up fitting inserts in the block where the valves had damaged the block.

Nearly made the same mistake the 2nd time till I checked the valve springs after assembly. A tweak with a screwdriver behind each one produced a slight “twang” on the one’s that were incorrect.

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Re: Destroying valve guides .. Need Help

Post by HoustonMule » Tue Mar 02, 2021 6:49 am

We checked that when tappet cover removed and all springs appeared to be sitting correctly in the machined pockets. Engine going back to machine shop and we'll be inspecting during teardown.

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Re: Destroying valve guides .. Need Help

Post by dpcd67 » Tue Mar 02, 2021 3:35 pm

Never had this happen and have no idea how it can happen. Valve train movement is pretty simple on L134. How can a guide wear oval in such a short time; Most engines go forever with little wear.
Maybe it has something to do with your lifters? Were they domed, or flat? I usually get new lifters, properly domed. If they are flat, the valves won't spin like they are supposed to.
Maybe your seats are not concentric with the guides? Your machine shop has to grind the seats piloted by the guide. If they did it the opposite way, that is potentially bad.
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Re: Destroying valve guides .. Need Help

Post by Chuck W. » Thu Mar 04, 2021 3:55 pm

Crown valve guides?

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Re: Destroying valve guides .. Need Help

Post by parker007 » Thu Mar 04, 2021 7:40 pm

im sceptical guide quality? it either bad parts or bad installation.

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Re: Destroying valve guides .. Need Help

Post by HoustonMule » Fri Mar 05, 2021 6:47 am

Teardown and inspection soon. Will advise on findings

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Re: Destroying valve guides .. Need Help

Post by dpcd67 » Fri Mar 05, 2021 1:46 pm

Right; I would ask them how exactly, they ground the new valve seats. I can't fathom any way a valve guide can wear like that except if it was installed and the seat was not ground concentric to the new guide. Using the new guide for the pilot. if you ground a seat using old guides, and then replaced the guide, that makes a potentially off center situation.
Just me thinking out loud. Well, not out loud; you know.
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Re: Destroying valve guides .. Need Help

Post by HoustonMule » Thu Apr 08, 2021 1:53 pm

Update: tappet bores worn as well as tappets. Bought new standard tappets but some are undersized according to spec data. Plus the bores are too worn to get back to the 0.0005 min and 0.002 max clearance. Now looking at buying 0.004 oversize tappets but will need to ream tappet bore. Who has the reamer needed????/

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Re: Destroying valve guides .. Need Help

Post by dpcd67 » Thu Apr 08, 2021 4:32 pm

So, it wasn't the valve guides after all? If it was the tappets, as now reported, then the machine shop didn't do it's job in the first place. I don't have the reamer.
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Re: Destroying valve guides .. Need Help

Post by HoustonMule » Fri Apr 09, 2021 8:52 am

The thought is after examining and measuring that the loose tappets were side loading the valves thus causing the guide wear. Contact markings of adjuster tip to valve stem tip showed this.

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Re: Destroying valve guides .. Need Help

Post by Joe Gopan » Fri Apr 09, 2021 9:46 am

NOTE:

Tappet Adjusting Screws are supposed to have a CONVEX WEAR SURFACE.
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