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Almost no compression

Posted By dennis22 4 Years Ago
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Stiggy
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Hitting on all eight cylinders

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dennis22 (8/15/2020)
Thanks Lord Gaga,

I did notice an inconsistency in the grey lapping markings on 2 intake valves. I’m wondering if I should have the machinist address these issues or if they are ok to leave? What do you guys think?

Good intake valve lap


Suspicious intake valve lap (I have done this one 3 times to see it it would come good)




Cliff
Posted 4 Years Ago
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Take it back
Lord Gaga
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On that second photo....looks like the valve or seat was ground at the wrong angle....who IS this guy?! I'd go somewhere else.

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dennis22
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Cliff, lord Gaga-

Yep I’ll take it back an have him fix those issues.

There are only 2 machinists in my area and the other guy takes months to do anything and Ive also had bad results using him. Unfortunately I’d have to travel 1 hour north or south from town for another machinist but wouldn’t even know where to look or who is good. Hence the fact I’m using this guy, I was recommended to him by a reputable mechanic.

3rd time lucky I hope🤞🤦‍♂️




Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.



dennis22
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I took all the valves back and asked for the 3 intake valves to be re-ground. I also took up 4 spare intake valves Incase there was an issue with the 3 valves.

So the machinist ground those 3 valves and also ground the spare 4 as back up spares. I get home and drop those 3 valves in for a lap (280grit) and check the result.... slightly better but not perfect. I pulled out one of the “good ground” valves to reference it against the newly ground valves and he has gone and re-ground all 16 valves + the 4 spare and made them worse than before. I was furious to say the least as I only asked for the 3 valves with issues to be ground.

I really need some expert advice on what a freshly ground valve should look like after lapping including recommended seat width, seat angle and back cut with angle.

This will be the 3rd time I have had to return for corrective work and just want some additional information so I know how to steer the conversation the correct direction. I have searched online but can’t pin down and useful information.

These are some of the valves, some look ok with a consistent contact band but others have 2 or 3 pronounced bands, others look like they have lots of broken bands where the compound was rubbing on high spots. From what I have read, the seat contact ‘band’ shouldn’t be too thick and should be consistent all the way through the seat contact.

Any feed back would be very much appreciated.











Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.



Lord Gaga
Posted 4 Years Ago
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Oh man, I feel for you.  He might not be dressing the grinding stones often enough...I don't know. You're right, The seats on some of those intakes look too wide. Also the contact should be more towards, but not at, the outer edges of the valves. In a perfect world that is. If this isn't a high performance engine and as long as the contact isn't too narrow and the valves seat and seal you'll be OK
Nothing more to offer but best wishes!

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Cliff
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The contact bands should be in the middle of the seat, .050 solid band all the way around, if the contact is closer to the rim of the valve that's fine, at this point your machinist is out to lunch, find a independent garage that has a valve grinder or if there is a speed shop by you talk to them.
dennis22
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I measured all the seats and the intake seat width varies from 0.060-0.102 and the exhaust from 0.043-0.060. In hindsight I should have asked all the question first but I have only learnt all this from this experience, as I trusted him to deliver, so I’ll head back to the shop and have him explain the process and what the parameter were that he set out to achieve and why are there such fluctuations.

Thanks LordGaga- Im about sick of it, but it’s been a great learning experience. I’ll ask if he uses a carbide cutter or stone. Part of me thinks it will be ok, but I don’t want to pull the heads off again later down the track so I want everything to be the best possible to ensure longevity.

Thanks Cliff- I will talk to him and see what he can do. Either correct his work or I’ll ask for a partial refund so I can have someone else correct the work.






Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.



Lord Gaga
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The seat width is very important to flow.

There are almost as many theories on seat width as there are head masters.

 Most of the machinists we spoke with prefer an intake-seat width of 0.040-0.060 inch. Narrower seats generally improve flow but are also less durable. Narrow seats work best on drag-race applications where the engine is freshened often. Harder seat materials (e.g., induction-hardened seats) allow you to run slightly narrower seat widths than in the past while retaining excellent durability. Since exhaust valves operate at extreme temperatures, they require a wider seat to conduct heat away from the valve through the seat. Most shops specify 0.060- to 0.080-inch seat width for the exhaust side.

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dennis22
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Thanks LordGaga,

I found that info online and thats what I’m using as my base line. I’ll see the machinist next week and go from there. I’m keen to drop this engine back in and get the truck running.


Thanks, Dennis.

56 F100 - 272 Y Block
NSW, Australia.





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