I have a 460 in a Mh,problem would not pass E-Test a low RPM.Have a misfire in #3 #7,cylinders's.55psi & 75psi,very low, leak down test,#3 exhaust valve leaking.Engine does burn oil 1/2 pint on 3000m trip down south.
Question #1 is it worth doing valve repair,#2 and will it improve performance i.e pulling power.
thanks for any input
Wg

 

wagib first let me welcome you to FTE I think you will find lots of usefull info here so browes around

Now for your question, you said the leak down showed #3 as having a bad exhaust valve,well what did #7 show? if it also indicates a bad valve but the rest of the engine is either low mileage or known to be in decent shape then I would say yes it's probably worth doing a valve job. but if it indicates you have a problem with the rings well then you should probably go ahead and pull the engine and at least do a minor rebuild in it with new rings, and bearings as well.
Other considerations are what is the oil preasure when hot? How many miles are on it? and how much work is it to get just the heads off of it, if you have to pull the engine to do the valve job I would probably go ahead and do the rings and bearings now as it's not really that expensive and might save you later on down the road.

 

Good call Monster. I would also recommend a new strait up timing set on any stock engine with more than 20,000 miles if ya got it out. I never do a light overhaul without new steel timing set. JMHO

 

You don’t say what year MH it is, but a valve job, at least, is in order. Since it is a motor home it probably doesn’t have much mileage on it. The oil consumption is minimal as the oil is probably going down the valve stems.

I have been towing a 7k 5th wheel with my 77F250 460 for over 20 years and during that time did some mods to the engine. Cam, Edelbrock carb, roller rockers, MSD ignition, double roller timing chain which performs better w/straight up timing, rings, bearings, valve job, etc. I have a 6 & 7 percent grade here in So Cal that I use for a test track. It is in a rural area and doesn’t have much traffic. I start out from a dead stop at the bottom and accelerate up the hill using mile makers to mark the speed. Every time I do a mod I hook the trailer up and go up the hill to measure the increase/decrease in performance. The most pronounced increase in performance came last year when I pulled the heads back off and put oversize manly stainless steel full flow racing valves in. I had previously had the smog bumps removed, but this time I purchased an air grinder and a porting and polishing kit and ported out the exhaust ports and polished them.

The increase in power was unbelievable, I crested the top of the hill 7mph faster than with the stock heads and the engine temp was 15 degrees cooler. If you plan on keeping the MH I would suggest that you take the heads to a good machine shop and do the same thing. It wont cost that much more than a stock valve job and would be well worth it. I would suggest that you buy the valves yourself and take them to the machine shop with the heads and have them installed. (That will save you a little money) Good luck Gary

 

Wb6vvv

Thanks for your reply also other reply's,it is a older MH 1990 and as 82000mi on the engine, uses very little oil just what you expect on the type of use.Also have no indication of bad rings.
Thanks

 

Welcom to FTI!!
I pulled my heads through the "DOG HOUSE" it wasn't that hard. I did have to get some of the exaust manafold bolts from underneath but verrey doable. The benifit of working on a motorhome versis some cars and trucks I have had is there is ushualey more room.
I would recomend a new timing set to. I would allso recomend a set of Doug ThorleyHeaders. http://www.dougthorleyheaders.com/
They help low end torque. Same desine as Banks but cheaper.
Bill

 

Hello Bill, I have heard so many wives tales on headers. Most of the people tell me that the stock iron manifolds on my 460 deliver as much low end torque as headers and the only advantage to headers is at high rpm. Which, for towing, I am not interested in. Do you have personal experience with the Doug Thorley headers increase in low end torque? I don't know if you read my post above about the increase in performance after doing my heads. I had a real chance to test it out last month. I have a friend with a motor home with a V10 in it. We took our annual 300 mile trek up north last month. He always pulled away from me on long grades, but this year I was right on his bumper all of the way. I will consider installing these headers if they will give me even more low end torque. Gary

 

I have a set of the TRI-Y Thorleys waiting to be installed. The problem with most headers is they are designed for racing and high rpm use. Racing headers have large diameter tubes that aren’t as good for low rpm use. The Thorleys and Banks set ups are designed (smaller diameter) for the lower rpm’s that tow trucks and motor homes see. I didn’t see any claims as to hp and lb-ft but when looking at Banks site the difference between the systems he sells one with headers and one with out. The difference with headers is 40 more HP from headers and 61 lb-ft more torque. I realize you may not get the same but I believe they are worth it.

The biggest thing you can do is get more air into your motor and more out.
Don't forget your crossover pipe eather a H or a X setup will allso help low end torque.

Bill

 

wagib, too bad your so far from me, I have a rebuilt set of 1990 heads from an F250 donor vehicle that I would like to sell. Shipping would probably kill us both. I am using the F3TE heads on my project and when I removed the heads from the 90 engine I found they had been rebuilt.

 

Thanks for the offer,would be big cost to ship and customs is a pain.
wagib