Welcome to our resource for MG Car Information.
Triumph TR6 - Cylinder Head Resurfacing
|I just removed the cylinder head from my 72' TR6. I was intending to have it milled .100, as I have seen suggested in numerous places. |
After examining the head, it would seem that .100 inches would be too much. It would actually be cutting into the shrould of the combustion chamber if I would go that deep. I am wondering if this head has already been cut. Does anyone have any measurements for this? It looks like the area between the exhaust valve and the head next to the spark plug is .578 inches from the deck of the head. The area of the chamber measures slightly greater than .560 inches to the surface of the head, depending on the area that you measure. Any help would be appreciated.
|Just taking material off the head is not a good move, you need to take the overall effect on your compression ratio into account. With current pump gas, you need to be careful about the compression ratio. Get it too high abd you will find that you must run octane boosters or race fuel. For myself, I fell that about 9.5:1 is about as high as I want to go these days on a street car that will run on pump gas, especially on these older cars that do not have knock sensors like newer cars.|
You need to determine the swept cylinder volume and any amount of dead space between the top of the piston at TDC and the block surface. You need to think about the volume of the bore through the head gasket and you also need to determine the volume of the combustion chambers for each cylinder. It is rather lengthy to describe here, but there are any number of books out there for building hot motors (any brand will do, i.e. "How to build hot rod Chevy small blocks" Everything you wanted to know about Ford Y blocks" etc) that go through all the steps for you. It will also include a list of tools/equipment that you will need. One thing we have found when measuring the combustion chamber volume is to use a colored liquid. We typically use a "menthol" rubbing alcohol that already has green dye in it. Having the color makes it much easier to read the graduation marks on the buret, clear on glass doesn't offer much in the way of contrast.
|Thanks for the response, Steve. After reading up on the subject, I did measure it. It turns out to be about 7.80:1. That puts it at stock, or uncut.|
It justs seems that the previous practice of cutting this down .100 looks like it would be too much. I think that I will reduce this to be on the safe side. Thanks again.
|Kip--The process SteveP describes is in fact the most correct approach. That said, I changed the CR on my '72 last year and have had no issues with detonation, although I do have to use premium gas because of run-on. I took a stock 4.550"-thick head from a '73 and shaved 0.120" off to 4.430". The machinist said there was plenty of meat left to go further, in fact. In combination with my 0.030" oversize pistons, that amount of shave puts me in the 9.5:1 CR range. I also had pushrods shortened by the same amount to maintain correct rocker geometry.|
All I can say is it has been a wonderful seat of the pants improvement with no ill effects other than the money spent. If you are unsure of your bores, when you pull the head clean the piston tops of carbon and see how they're marked. If they are standard, you can certainly shave more than 0.100" if you have the money.
|Thanks, Steve. I will have the machinist check it out. I also noted that the pushrod geometry would be affected.|
Have you thought of valve stem seals? I notice that Triumph doesn't use them. I was wondering if I should have them added.
|Opinions are mixed on valve stem seals. There are those that swear by running nothing, others that take an approach similar to that used on MGs with a square section o-ring and others that like a cup type valve stem seal (i.e. what most people think of when they think valve stem seal). For myself, I like valve stem seals.|
The first and second approach can be done with no problem. The cup type seals get a little trickier. If you engine has the single springs, I have found some Perfect Circle valve stem seals (VS19 if I am remembering the part number) that can be used on the stock guides and that will fit inside the spring diameters. If you have the double springs, then the guides must be flycut so seals with a smaller outer diameter can be fitted since the inner diameter of the double spring set up is smaller.
My recommendation if you are having head work done is to go ahead and have everything done for a proper unleaded fuel conversion, use the bronze guides and hardened valve seats. If new guides are going in, they can be turned on lathe prior to installation instead of having them flycut after installation for the valve stem seals. Also, let the guy doing the head work set up your springs. This is especially true if running a non-stock cam. You will need to know what spring seat pressure the cam producer recommends. When the springs are set up, the install height can be adjusted to obtain that pressure and be checked to ensure that you do not get into a coil bound situation at full cam lift/valve opening. You can also take the opportunity while the head is off to do some port matching.
This thread was discussed between 30/01/2005 and 02/02/2005
Triumph TR6 index
This thread is from the archive. The Live Triumph TR6 BBS is active now.